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SCHG

Nem s2b

From Sonic Retro

Historical document icon.svg

This historical hacking document is preserved here for archival purposes.
It has not been revised since its original writing and may be outdated. For an SCHG-equivalent document, see SCHG:Sonic 2 Beta.


Introduction

Here are my hacking notes on the Sonic 2 rom. If you use these notes I'd appreciate it if you would mention it with your hack or your utility, so that other people can find their way here. For hex editing I recommend you use a hex utility called Hex workshop, and for emulators I recommend you get both Gens and Genecyst. Genecyst may be old and kinda crap, but it has a whole heap of debug outputs that really help when it comes to seeing exactly what it's doing and when.

First of all it's very important that you understand the basics. All data stored on a computer is in the form of 1's and 0's. On a CD for example, a laser hits the surface, and if the laser bounces back and hits the lens it's a 1, and if it doesn’t it's a zero. Each 1 or 0 is called a bit, and a bit cannot have any other characters in it other that a 1 or a 0. Now the computer deals with bits in groups of 4. There are 16 possible combinations for a group of four 1's and 0's, so to make it simpler it deals with it as one value, rather than 4 (Eg. 0110 becomes 6). Now as there are 16 possible combinations for a group of 4 bits, this value to represent their values must have 16 values itself, so rather than a simple 0-9, this value is 0-F (0123456789ABCDEF). This value is called a hexadecimal value (hex value for short). Each hex value is dealt with in groups of 2, called a byte, each byte having 128 possible combinations. Now on a final output level the byte may be looked up on an ASCII table, which will convert that value into a recognisable character (Eg. a byte value of 73 becomes a lowercase s on an English ASCII table). You will practically never touch the ASCII version of the code in hacking though.


Now one important thing to realise is that as one character of hex has 16 values and a decimal (real) value only has 10, it may be necessary to convert the numbers between them from time to time. This is done with the use of a base converter (included in hex workshop). Let's say you wanted to give Sonic 50 rings. If you enter 50 as the value, you will in fact end up with 80, because that value you are entering is actually a hex value, but if you use the base converter to convert it first, you merely enter the value of 50 into the decimal box, and it will spit out a hex value of 32, which will in fact give you 50 rings in the game. Another useful utility that you will need is a hex calculator (also included in hex workshop). A hex calculator is the same as a normal calculator, but it deals with hex values rather than decimal values.

Another thing you need to know is that each level in Sonic 2 has a value assigned to it, but this value does not correspond with each level's final position in the game. Here is a list of the level values in Sonic 2 beta:

00 Emerald Hill zone
02 Wood zone
04 Metropolis zone
05 Metropolis zone act 3
07 Hill Top zone
08 Hidden Palace zone
0A Oil Ocean zone
0B Dust Hill zone
0C Casino Night zone
0D Chemical Plant zone
0E Genocide City zone
0F Neo Green Hill zone
10 Death Egg zone


One other thing you need to know is the way that the Mega Drive stores all the art. All the art that is used in the game is stored in the form of 8x8 pixel blocks. These blocks do not actually store colours at all, they actually only have one hex value per pixel. That value specifies what point on the palette line the pixel will get its colour from. The palette has 4 lines, each with 16 colours on them. Now the colours on the palette can be changed at any point during play, and some palette colours may even automatically change colour each couple of frames to make it look like the colour is flashing.

Now these 8x8 blocks are not what make up the level directly. 4 8x8 blocks are grouped together to form a 16x16 block, and it is at this point that the palette line to use for that 16x16 block is specified. The 8x8 patterns can also have their x, y, or x and y values reversed when placing them in a 16x16 block. Also it's at the 16x16 level that the collision definitions are specified. Now finally we get to a 128x128 block, and these are the things that the actual level info loads. It is made up of 64 16x16 blocks, and each block inside them can use a different palette line. You cannot place anything except a sprite or a 128x128

block directly into a level.


Now that you know all the basics, here's my breakdown:

Address listing

For the most part, there are no breaks in this list. If one address follows on directly from another on this list, it does so in the rom, with the exception of data that comes before 20000. All the compiled code that is used in the game is stored in this section, and that's a pain in the ass to sort through, so there will be many breaks there. The column on the left lists it's file location, the column in the middle contains it's name and description, and the column on the right will contain any special notes about it, such as compression format used if applicable, and number of blocks an art tile uses. The right column will also contain a link with the text further info, if that particular block requires it. That link will jump to a detailed explanation of that thing. Anything linked like that will also be listed in the contents at the top of the page.

To indicate sections containing leftover data from previous builds, a colour coding system is in place. The address value for a block of data will be coloured if that block of data is from a previous build. Different colours are used to indicate layering of this data. Red is the first layer, green is the second, blue is the third, yellow is the fourth, and pink is the fifth. This is not to indicate the build that a block of data belongs to, so it doesn't mean that all lost data that's coloured in red is from the same build. In many cases, it's impossible to relate any two blocks of data from different sections to each other.

Also, any patterns that are not used anywhere in the game will be preceeded by this red dot Reddot.gif. Patterns located in sections of lost data will not be marked in this way however.

0-FF Vector table
100-200 Header
15FA-???? Programming to do wih decompression of art tiles to VRAM Compiled
5E8-B07 Standard numbers/symbols Uncompressed
Further info
2264-24A1 Unknown palettes Further info
2516-2595 Unknown palette Further info
28A6-28E1 Unknown palette Further info
294E-2A15 Palette pointers Further info
2A16 SEGA screen palette (00) Further info
2A96 Title screen palette (01) Further info
2B16 Level select palette (02) Further info
2B96 Primary palette line (03) Further info
2BB6 EHZ level palette (04, 05, 07, 0D, 12, 14) Further info
2C16 WZ level palette (06) Further info
2C76 MTZ level palette (08, 09) Further info
2CD6 HTZ level palette (0B) Further info
2D36 HPZ level palette (0C) Further info
2D96 HPZ underwater palette (15) Further info
2E16 OOZ level palette (0E) Further info
2E76 MCZ level palette (0F) Further info
2ED6 CNZ level palette (10) Further info
2F36 06 level palette (0A) Further info
2F96 CPZ level palette (11) Further info
2FF6 CPZ underwater palette (15) Further info
3076 ARZ level palette (13) Further info
30D6 ARZ underwater palette (16) Further info
3156 Sonic 1 special stage palette (17) Further info
3AD4-3B07 Level select level order Further info
4140-4150 Music playlist for levels Further info
4AAA-4ADB Function to load collision index into ram Compiled
4ADC-4B63 Pointers to collision indexes Further info
5986-5A95 Level size array Further info
5A96-5B01 Code for initial character and screen placement Compiled
5B02-5B89 Character start location array Further info
5E16-5E37 Offset index of rasterised layer deformation Further info
5E38 Title screen layer deformation info Further info
5E5C EHZ layer deformation info Further info
5F60 EHZ 2 player splitscreen layer deformation info Further info
6098 WZ layer deformation info Further info
60D0 MTZ layer deformation info Further info
6108 HTZ layer deformation info Further info
6236 Unknown layer deformation info (foreground free moving, background fixed) Further info
62B4 Unknown layer deformation info (splitscreen, background fixed vertically, no deformation) Further info
6344 HPZ layer deformation info Further info
640A OOZ layer deformation info Further info
6442 MCZ layer deformation info Further info
6554 Unknown layer deformation info (splitscreen, background fixed horizontally, no deformation) Further info
67AE CNZ layer deformation info Further info
67F2 Unknown layer deformation info (splitscreen, background fixed vertically, no deformation) Further info
687C CPZ layer deformation info Further info
6982 ARZ layer deformation info Further info
6A70 01, 03, 06, 09, 0E, 10 layer deformation info Further info
7FDC Bridge (sprite)
85F8 ??????? (sprite)
8B9C ??????? (sprite)
8D38 Fixed large platform from CPZ (sprite)
9128 Collapsing platform from OOZ (sprite)
9274 Breakaway platform made up of small blocks from MZ in S1 (sprite)
999C ??????? (sprite)
9A54 ??????? (sprite)
9C0C ??????? (sprite)
9CE2 ??????? (sprite)
A012 ??????? (sprite)
A086 Explosion giving off 100 points and an animal (sprite)
A11E Red explosion (sprite)
A2B0 ??????? (sprite)
A7C0 100 points (sprite)
AC28 ??????? (sprite)
AD62 Ring spray (sprite)
B29C ??????? (sprite)
B46A Contents of computer monitor flying up (sprite)
B7B4 ??????? (sprite)
B83A ??????? (sprite)
BB54 ??????? (sprite)
BD76 Game over text (sprite)
BE38 ??????? (sprite)
BF9A-BFDD Main game level order Further info
C944 Spikes (sprite)
CD00 Unknown (a block)
CD7C ??????? (sprite)
D01A-D249 Sprite programming pointers Further info
D24A ??????? (sprite)
E7B8 Horizontal red spring (sprite)
F10C ??????? (sprite)
F1F4 Signpost (sprite)
FC48 Sonic (sprite)
10E38 Tails (sprite)
11F96 ??????? (sprite)
1207C ??????? (sprite)
125CE ??????? (sprite)
1264E ??????? (sprite)
12B42 ??????? (sprite)
13B54 Starpoll (sprite)
13DFC ??????? (sprite)
144B0 ??????? (sprite)
148AC ??????? (sprite)
149FC ??????? (sprite)
14AFC ??????? (sprite)
14B78 ??????? (sprite)
15090 ??????? (sprite)
15352 ??????? (sprite)
155A0 ??????? (sprite)
1561A ??????? (sprite)
1572C ??????? (sprite)
15B8C See-saw (sprite)
1600C Diagnally moving and falling platform from HTZ (sprite)
1621C Large platform from CPZ moving from side to side (sprite)
16468 Boosters from CPZ (sprite)
165B0 ??????? (sprite)
16724 Spin-tube from CPZ (sprite)
17174 ??????? (sprite)
1747C ??????? (sprite)
1768A Cap on top of spin tubes in CPZ (sprite)
17A4C ??????? (sprite)
17CA0 Platform on top of oil burners from OOZ (sprite)
17F0C Spikeball from OOZ (sprite)
180D0 ??????? (sprite)
181A0 Weird spring that you push back on from OOZ (sprite)
18ABE Ball on weird spring from OOZ (sprite)
18D9C Button (sprite)
18E78 Block that propells sonic when he busts it from OOZ (sprite)
19250 Spinball that shoots character out 90 degrees from entry from OOZ (sprite)
19660 Arrow shooter from ARZ (sprite)
19850 Piller that drops lower half in ARZ (sprite)
19A1E Raising pillar from ARZ (sprite)
1A0C4 ??????? (sprite)
1A30C Weird spring from ARZ and CPZ (sprite)
1A5CC Steam vent from MTZ (sprite)
1A8B4 ??????? (sprite)
1AA74 ??????? (sprite)
1AEBC ??????? (sprite)
1B0C4 Warp tube from MTZ (sprite)
1B520 Block in MTZ with a spike coming out each side sequentially (sprite)
1B810 Nut that character moves by running on in MTZ (sprite)
1BA30 ??????? (sprite)
1BCEC ??????? (sprite)
1BF6C ??????? (sprite)
1B720 Floor spike in MTZ (sprite)
1C2E4 Platform moving in circle (sprite)
1C4F8 Diagnally moving platform from MTZ (sprite)
1C850 ??????? (sprite)
1CBCC ??????? (sprite)
1CC54 ??????? (sprite)
1CE48 ??????? (sprite)
1D078 Moving spikey arm from MCZ (sprite)
1D208 ??????? (sprite)
1D3C0 Lowering stairs from CPZ (sprite)
1D594 ??????? (sprite)
1D74C Spring on spin tube cap from CPZ (sprite)
1D984 Driving badnick from EHZ (sprite)
1DC54 ??????? (sprite)
1DEAC Bubble enemy (sprite)
1E010 ??????? (sprite)
1E62C ??????? (sprite)
1E89C Buzz bomber (sprite)
1EBB8 Octopus badnick from OOZ (sprite)
1EE68 Bat (sprite)
1F2F0 Alligator (sprite)
1F5E8 Jumping fish from EHZ (sprite)
1F6E8 ??????? (sprite)
1F99C ??????? (sprite)
1FC0A ??????? (sprite)
2030C ??????? (sprite)
205A6 ??????? (sprite)
20740 ??????? (sprite)
20E5C ??????? (sprite)
21D40 ??????? (sprite)
223E2 ??????? (sprite)
22408 Offset index of animated pattern and dynamic pattern load cue's Double offset
Further info
2244C 01/WZ/03/06/09/MCZ/CNZ/GCZ/DEZ dynamic pattern load cue Further info
2244E HTZ dynamic pattern load cue Further info
22630 EHZ/HPZ/MTZ/OOZ/CPZ/ARZ dynamic pattern load cue Further info
22698 EHZ animated pattern load cue (4) Further info
226FC MTZ animated pattern load cue (5) Further info
22754 HTZ animated pattern load cue (4) Further info
227B8 HPZ animated pattern load cue (2) Further info
227E4 OOZ animated pattern load cue (4) Further info
2282A CPZ animated pattern load cue (0) Further info
22866 01/WZ/03/06/09/MCZ/CNZ/GCZ/DEZ animated pattern load cue (empty) Further info
229A2 Offset index of misc sprite definitions Further info
229C4 EHZ/HTZ misc sprite definitions Further info
22A40 MTZ misc sprite definitions Further info
22B14 HPZ misc sprite definitions Further info
22C08 OOZ misc sprite definitions Further info
22C6C CNZ misc sprite definitions Further info
22D10 CPZ misc sprite definitions Further info
22D1C ARZ misc sprite definitions Further info
22D60 01/WZ/03/06/09/MCZ/GCZ/DEZ misc sprite definitions Further info
22DFC Onscreen display (lives/score/time/rings) (sprite)
23448-23B67 Large and small numbers used in game Uncompressed
Further info
23DBE Offset index of object debug lists Further info
23DE0 01/WZ/03/06/09/GCZ/DEZ object debug list Further info
23DF2 EHZ object debug list Further info
23ECC MTZ object debug list Further info
23FAE HTZ object debug list Further info
24078 HPZ object debug list Further info
240F2 OOZ object debug list Further info
24194 MCZ object debug list Further info
24216 CNZ object debug list Further info
24228 CPZ object debug list Further info
242C2 ARZ object debug list Further info
24354 Indexed main level load block Further info
24420 Offset index of pattern load cue's Further info
2447A Pattern load cue's Further info
24804 Lost pattern load cue's from previous compilation Further info
24A30 Leftover data from previous build
28000 Animated cone shaped flower from EHZ and HTZ Uncompressed
Further info
28080 Animated bubble like flower from EHZ and HTZ Uncompressed
Further info
28100 Animated stringy flower from EHZ and HTZ Uncompressed
Further info
28180 Animated leafy flower from EHZ and HTZ Uncompressed
Further info
28200 Animated pulsing thing against checkered background in EHZ Uncompressed
Further info
28300 Hills in background from HTZ Art compression
192 blocks
28C2A Clouds in background of HTZ Uncompressed
Further info
2902A Spinning metal cylinder from MTZ Uncompressed
Further info
2A02A Lava patterns from EHZ and MTZ Uncompressed
Further info
2A62A Animated section of MTZ background Uncompressed
Further info
2A86A Horizontal and vertical rotating screw Uncompressed
Further info
2B06A Weird peice of alpha HPZ background Uncompressed
Further info
2B46A Giant pulsing ball in HPZ Uncompressed
Further info
2B76A Tiny pulsing ball in OOZ Uncompressed
Further info
2B94A Square rotating around ball in OOZ Uncompressed
Further info
2BD4A Oil in OOZ Uncompressed
Further info
2CCEA Animated background section from CPZ and DEZ Uncompressed
Further info
2CEEA Waterfall patterns from ARZ Uncompressed
Further info
2D1EA Curve and resistance mapping Further info
2D2EA Collision array Further info
2F2EA EHZ and HTZ primary 16x16 collision index Further info
2F5EA EHZ and HTZ secondary 16x16 collision index Further info
2F8EA WZ primary 16x16 collision index Further info
2FBEA MTZ primary 16x16 collision index Further info
2FEEA HPZ primary 16x16 collision index Further info
301EA HPZ secondary 16x16 collision index Further info
304EA OOZ primary 16x16 collision index Further info
307EA DHZ primary 16x16 collision index Further info
30AEA CNZ primary 16x16 collision index Further info
30DEA CNZ secondary 16x16 collision index Further info
310EA CPZ primary 16x16 collision index Further info
313EA CPZ secondary 16x16 collision index Further info
316EA ARZ primary 16x16 collision index Further info
319EA ARZ secondary 16x16 collision index Further info
31CEA-3334D ????????? (something to do with special stage)
3334E Level layout offset index Unique offset
Further info
333D6 EHZ act 1 foreground Further info
33BD8 EHZ act 2 foreground Further info
343DA EHZ act 1/2 background Further info
343E4 01 act 1/2 foreground/background Further info
343E8 WZ act 1 foreground Further info
34BEA WZ act 2 foreground Further info
353EC WZ act 1 background Further info
35BEE WZ act 2 background Further info
363F0 03 act 1/2 foreground/background Further info
363F4 MTZ act 1 foreground Further info
36BF6 MTZ act 2 foreground Further info
373F8 MTZ act 1/2/3 background Further info
3741E MTZ act 3 foreground Further info
37C20 06 act 1/2 foreground/background Further info
37C24 HTZ act 1 foreground Further info
38426 HTZ act 2 foreground Further info
38C28 HTZ act 1 background Further info
3942A HTZ act 2 background Further info
39C2C HPZ act 1/2 foreground Further info
3A42E HPZ act 1/2 background Further info
3A478 09 act 1/2 foreground/background Further info
3A47C OOZ act 1 foreground Further info
3AC7E OOZ act 2 foreground Further info
3B480 OOZ act 1/2 foreground/background Further info
3B49A DHZ act 1 foreground Further info
3BC9C DHZ act 2 foreground Further info
3C49E DHZ act 1/2 background Further info
3C4B0 CNZ act 1 foreground Further info
3CCB2 CNZ act 2 foreground Further info
3D4B4 CNZ act 1 background Further info
3DCB6 CNZ act 2 background Further info
3DCC0 CPZ act 1 foreground Further info
3E4C2 CPZ act 2 foreground Further info
3ECC4 CPZ act 1 foreground Further info
3ECF0 GCZ act 1/2 foreground/background Further info
3ECF4 ARZ act 1 foreground Further info
3F4F6 ARZ act 2 foreground Further info
3FCF8 ARZ act 1 background Further info
404FA ARZ act 2 background Further info
40CFC DEZ act 1/2 foreground/background Further info
40D00 Giant golden ring Uncompressed
Further info
41940 Blank space
42B7A Giant golden ring... again (uncompressed)
437BC Very end of palette
437C6 ??????????
44000 Offset index of sprite locations Further info
4404A EHZ act 1 sprite locations Further info
442C6 EHZ act 2 sprite locations Further info
445C0 MTZ act 1 sprite locations Further info
4488A MTZ act 2 sprite locations Further info
44B30 MTZ act 3 sprite locations Further info
44EFC HTZ act 1 sprite locations Further info
45130 HTZ act 2 sprite locations Further info
4554A HPZ act 1 sprite locations Further info
45652 HPZ act 2 sprite locations (empty) Further info
45658 Unknown (empty) Further info
4565E OOZ act 1 sprite locations Further info
457C0 OOZ act 2 sprite locations Further info
459AC DHZ act 1 sprite locations Further info
45A24 DHZ act 2 sprite locations Further info
45A2A CPZ act 1 sprite locations Further info
45CC4 CPZ act 2 sprite locations Further info
4605A ARZ act 1 sprite locations Further info
46216 ARZ act 1 sprite locations Further info
46348 01, WZ, 03, 06, 09, CNZ, GCZ, DEZ sprite locations (empty) Further info
4634E ??????????
474AC Lost palette
4760C ??????????
48000 Offset index of ring locations Further info
48044 EHZ act 1 ring locations Further info
481DE EHZ act 2 ring locations Further info
483DC 01 act 1 ring locations (empty) Further info
483DE 01 act 2 ring locations (empty) Further info
483E0 WZ act 1 ring locations (empty) Further info
483E2 WZ act 2 ring locations (empty) Further info
483E4 03 act 1 ring locations (empty) Further info
483E6 03 act 2 ring locations (empty) Further info
483E8 MTZ act 1 ring locations (empty) Further info
483EA MTZ act 2 ring locations (empty) Further info
483EC MTZ act 3 ring locations (empty) Further info
483EE MTZ act 4 ring locations (empty) Further info
483F0 06 act 1 ring locations (empty) Further info
483F2 06 act 2 ring locations (empty) Further info
483F4 HTZ act 1 ring locations Further info
484EA HTZ act 2 ring locations Further info
48654 HPZ act 1 ring locations Further info
487C6 HPZ act 2 ring locations (empty) Further info
487C8 09 act 1 ring locations (empty) Further info
487CA 09 act 2 ring locations (empty) Further info
487CC OOZ act 1 ring locations Further info
4889E OOZ act 2 ring locations Further info
48968 DHZ act 1 ring locations (empty) Further info
4896A DHZ act 2 ring locations (empty) Further info
4896C CNZ act 1 ring locations (empty) Further info
4896E CNZ act 2 ring locations (empty) Further info
48970 CPZ act 1 ring locations Further info
48A3E CPZ act 2 ring locations Further info
48B94 GCZ act 1 ring locations (empty) Further info
48B96 GCZ act 2 ring locations (empty) Further info
48B98 ARZ act 1 ring locations Further info
48C76 ARZ act 2 ring locations Further info
48DB0 DEZ act 1 ring locations (empty) Further info
48DB2 DEZ act 2 ring locations (empty) Further info
48DB4 ??????????
4B76C Rock splashing into liquid (uncompressed)
4BAAC Lost palette
4BC4C ??????????
4E54A Grains of sand falling (uncompressed)
4E86A Fire in bowl against stone background (uncompressed)
4EC6A Data block acting as seperator
4EE00 ?????????? (uncompressed data blocks with massive repetition)
4FB98 Data block acting as seperator
50000 Patterns for Sonic Uncompressed
Further info
614C0 Unknown offset index Further info
6160E Unknown (Something to do with mappings for Sonic) Further info
62598 Patterns for Tails Uncompressed
Further info
6DA4C Unknown offset index Further info
6DB9A Unknown (Something to do with mappings for Sonic) Further info
6DF8E Patterns for bubble Art compression
32 blocks
6E114 Stars from invincibility Art compression
00, 34 blocks
6E1F6 Patterns for smoke trails, dust, and splash in water Uncompressed
Further info
6FB3C Unknown offset index Further info
6FC46 Unknown (Something to do with mappings for Tails) Further info
7056E Unknown offset index Further info
70678 Unknown (Something to do with mappings for Tails) Further info
70960 SEGA patterns Art compression
125 blocks
71520 Title patterns Art compression
396 blocks
72E82 Sonic patterns in title screen Art compression
193 blocks
739C6 Fireballs from HTZ and WZ Art compression
20 blocks
73B3C Some waterfll tiles form WZ Art compression
24 blocks
73C42 Another fireball from HTZ Art compression
00, 16 blocks
73D90 Peices of bridge from EHZ Art compression
00, 8 blocks
73E68 Flying fox system in HTZ Art compression
48 blocks
7415C One way barrier from HTZ Art compression
4 blocks
741D4 See-saw from HTZ Art compression
24 blocks
Reddot.gif7436C Fireball Art compression
18 blocks
7447A Rock from HTZ Art compression
20 blocks
745B0 badnick from HTZ with balls of flame spinning around him that he shoots at you Art compression
4 blocks
7461C Spinning grey wheel from MTZ Art compression
120 blocks
74A74 A ball shaped thing from MTZ patterns Art compression
9 blocks
74B1C Spear block from MTZ Art compression
00, 8 blocks
74BEA Steam from MTZ Art compression
00, 15 blocks
74CF4 Spike from MTZ Art compression
00, 8 blocks
74DB6 Unknown. Some similar shaded blocks Art compression
54 blocks
74E2C Lava bubble from MTZ Art compression
00, 9 blocks
74EE2 Something from MTZ patterns Art compression
4 blocks
74F52 Unknown. A block of some kind. Art compression
32 blocks
751FE Stuff from MTZ Art compression
8 blocks
752A0 Mini rotating cog from MTZ Art compression
12 blocks
75382 Four blocks from MTZ tiles. All of the blocks are just one colour Art compression
00, 04 blocks
7538E Bridge from HPZ Art compression
21 blocks
75506 Waterfall tiles for HPZ Art compression
53 blocks
75868 The master emerald Art compression
32 blocks
75ADA Platform thing from HPZ Art compression
16 blocks
75B9A Pulsing light thing from HPZ Art compression
34 blocks
75DD6 Another platform thing from HPZ and those green blocks Art compression
22 blocks
75F70 Patterns from raising platform in OOZ Art compression
12 blocks
76060 Spikeball thing from OOZ Art compression
00, 32 blocks
76258 Patterns for stuff in OOZ Art compression
6 blocks
762EE Some striped patterns from OOZ Art compression
4 blocks
7635A Oil patterns from OOZ Art compression
16 blocks
764D6 Some blocks of oil and stuff from OOZ Art compression
14 blocks
76602 Unknown. Damn I wish I could make this out, because it looks quite interesting. Art compression
20 blocks
76722 Unknown. Ditto. Art compression
53 blocks
76A12 Unknown. Whatever they are, they look OOZ style. Art compression
40 blocks
76CA6 Unknown. Also look OOZ in style. Art compression
30 blocks
76E68 Swinging platform from OOZ Art compression
28 blocks
7708A Wooden box from MCZ Art compression
32 blocks
772C8 Collapsing platform from MCZ Art compression
00, 26 blocks
77472 Vines around switch you pull on from MCZ Art compression
16 blocks
7756A Vines from MCZ Art compression
10 blocks
77614 A side on view of a log from WZ I suspect. Art compression
00, 4 blocks
77684 Big moving platform in CPZ Art compression
00, 16 blocks
777D2 Surface of water from HPZ and CPZ Art compression
00, 24 blocks
77942 Unknown. It looks like a small cylinder kinda. Art compression
00, 4 blocks
779AA Blue ball for enemy in CPZ Art compression
00, 4 blocks
77A1C CPZ metal stuff Art compression
33 blocks
77C26 Some blocks from CPZ Art compression
4 blocks
77C66 Some diagnally striped blocks from CPZ Art compression
8 blocks
77CD2 Little yellow moving platform from CPZ Art compression
48 blocks
77EB4 Block from CPZ, but with something else as well. Art compression
24 blocks
78074 Spring on top of pipe from CPZ, and something else further down. Art compression
32 blocks
78270 Top of water from ARZ Art compression
00, 16 blocks
78356 Leaves from ARZ Art compression
00, 7 blocks
783E2 Arrow and arrow shooter from ARZ Art compression
00, 17 blocks
78540 Splash from ARZ Art compression
00, 4 blocks
78580 Button Art compression
16 blocks
78658 Vertical red spring Art compression
00, 20 blocks
78774 Horizontal red spring Art compression
12 blocks
7883E Diagonal spring Art compression
32 blocks
78A12 Score, rings, time patterns Art compression
24 blocks
78B1A Sonic lives counter Art compression
12 blocks
78C30 Ring patterns Art compression
00, 14 blocks
78D24 Monitor patterns Art compression
60 blocks
7914E Spikes Art compression
8 blocks
7919E Numbers Art compression
18 blocks
79278 Beta starpoll Art compression
10 blocks
7931E Signpost for end of level Art compression
82 blocks
798F4 Weird spring from CPZ and ARZ Art compression
00, 28 blocks
79A44 Long horizontal spike Art compression
00, 8 blocks
79AC0 Bubbles and numbers that count down when underwater Art compression
00, 116 blocks
Reddot.gif7A11A Crocodile Art compression
00, 44 blocks
7A4BC Buzz bomber Art compression
00, 28 blocks
7A6A2 Bat from HPZ Art compression
00, 58 blocks
Reddot.gif7A9F8 Octopus from OOZ Art compression
00, 58 blocks
Reddot.gif7AD18 Rhinobot Art compression
00, 5 blocks
7B114 Dinobot Art compression
00, 48 blocks
Reddot.gif7B4EA Pirhana Art compression
00, 64 blocks
Reddot.gif7B9E2 Seahorse from OOZ Art compression
00, 62 blocks
Reddot.gif7BE30 Spinning ball thingy Art compression
00, 27 blocks
Reddot.gif7C0C6 Blinky Art compression
24 blocks
Reddot.gif7C2F2 Bubble monster Art compression
00, 24 blocks
7C514 Ground based badnick from EHZ Art compression
26 blocks
Reddot.gif7C710 Bouncer badnick from CNZ Art compression
00, 42 blocks
7CA92 Fish badnick from EHZ Art compression
22 blocks
7CC9E Robotnic and his main ship Art compression
96 blocks
Reddot.gif7D3DA CPZ boss Art compression
111 blocks
7D938 Some kind of large explosion Art compression
00, 100 blocks
7DFC0 A small explosion Art compression
00, 8 blocks
7E03E Some kind of trailing smoke Art compression
00, 16 blocks
7E124 EHZ boss Art compression
128 blocks
7E910 Chopper blades for EHZ boss Art compression
00, 20 blocks
7EA04 Title card patterns for levels Art compression
128 blocks
7F012 Regular in level explosion Art compression
96 blocks
7F678 Game/time over tiles Art compression
34 blocks
Reddot.gif7F80A Vertical spring from S1 Art compression
00, 16 blocks
Reddot.gif7F90C Horizontal spring from S1 Art compression
14 blocks
Reddot.gif7F9E8 Flash from entering giant ring Art compression
84 blocks
Reddot.gif7FB5C Hidden end of level bonus points Art compression
00, 36 blocks
Reddot.gif7FE5E Patterns for continue screen from S1 Art compression
37 blocks
Reddot.gif8010E Patterns for recieveing continue at end of special stage from S1 Art compression
30 blocks
80348 Rabbit Art compression
00, 18 blocks
804A0 White bird Art compression
14 blocks
805FC Black bird Art compression
00, 18 blocks
80778 Seal Art compression
00, 14 blocks
80894 Pig Art compression
18 blocks
809CA Blue bird Art compression
00, 14 blocks
80B04 Bear Art compression
00, 18 blocks
80C60 16x16 block mappings for EHZ Further info
81C00 EHZ/HTZ main level patterns Art compression
912 blocks
84A50 16x16 block mappings for HTZ suppliment on EHZ tiles Further info
85200 HTZ pattern suppliment to EHZ level patterns Art compression
386 blocks
86626 Initial blocks for dynamically reloaded and animated patterns in HTZ Art compression
46 blocks
8692E EHZ/HTZ 128x128 block mappings Compressed
Further info
89B8E WZ 16x16 block mappings Further info
8AB2E WZ main level patterns Art compression
798 blocks
8E826 WZ 128x128 block mappings Compressed
Further info
90456 MTZ 16x16 block mappings Further info
91716 MTZ main level patterns Art compression
783 blocks
94C56 MTZ 128x128 block mappings Compressed
Further info
97596 HPZ 16x16 block mappings Further info
98B76 HPZ main level patterns Art compression
725 blocks
9B9F8 HPZ 128x128 block mappings Compressed
Further info
9D778 OOZ 16x16 block mappings Further info
9ED58 OOZ main level patterns Art compression
693 blocks
A1A58 OOZ 128x128 block mappings Compressed
Further info
A3F88 MCZ 16x16 block mappings Further info
A5248 MCZ main level patterns Art compression
936 blocks
A8B6A MCZ 128x128 block mappings Compressed
Further info
AB5CA CNZ 16x16 block mappings Further info
ABF2A CNZ main level patterns Art compression
850 blocks
AE746 Leftover data from previous build
AEF3C Some blocks from CNZ Art compression
22 blocks
AF026 CNZ 128x128 block mappings Compressed
Further info
B0F26 CPZ/DEZ 16x16 block mappings Further info
B2506 CPZ/DEZ main level patterns Art compression
858 blocks
B6058 CPZ/DEZ 128x128 block mappings Compressed
Further info
B8558 ARZ 16x16 block mappings Further info
B9E58 ARZ main level patterns Art compression
1002 blocks
BF408 Waterfall patterns Art compression
00, 11 blocks
BF568 ARZ 128x128 block mappings Compressed
Further info
C2138 End of compressed ARZ 128x128 block mappings Further info
C2148 large chunk of CNZ 128x128 block mappings (uncompressed) Further info
C943C CPZ 16x16 block mappings (Different to current beta) Further info
CAA1C CPZ main level patterns (797 blocks) (Different to current beta) Further info
CE03A CPZ 128x128 block mappings (uncompressed) (Different to current beta) Further info
D603A ARZ 16x16 block mappings
D793A ARZ main level patterns (1002 blocks) (Identical to current beta)
DCEEA Waterfall patterns (00, 11 blocks)
DD04A ARZ 128x128 block mappings (uncompressed) (Different to current beta)
E504A Incomplete part of ARZ main level patterns (Identical to current beta)
E57E6 Waterfall patterns (00, 11 blocks)
E5946 Compressed ARZ 128x128 block mappings Further info
E8000 Half of SEGA intro sound Further info
EC000-ECFFF ??????????
ED000-EFFFF ?????????? (Something to do with music)
F0000-F1E8B ?????????? (Something to do with music)
F1E8C-F7FFF SEGA intro sound 16000Hz mono
8-bit unsigned
PCM raw audio
Further info
F8000-FEFFF ?????????? (Something to do with music)
FF000-FFFFF ?????????? (Something to do with sound fx)

Offset indexes

An offset index is a handy way of keeping a block of data grouped together, and also replacing a whole heap of pointers. The way it works is there is a list of two byte vaues, and depending on the block of data the game wants to load, it will take one of those values and add it to the starting address of the offset index. The most common usage is for every act of every level value, there is an offset that acts as the pointer to the block of data to use for it. Lets look at an example:

E6800: 004A 037A 5552 5552 5552 5552 5552 5552 0734 0BC0 10EE 10EE 1748 1AFC

Now this is the beginning of the offset index for the sprite locations. Now, can you see which values are the offset for MTZ act 2? They're 0BC0. All you had to do to get that was to take the level value for MTZ, which is 04, and count across four bytes for every value it is above 00, then across another two because it's the second act. Now we take that value and using a hex calculator, add it to the address of the offset table, which is E6800. That will give us a value of E73C0, which is the address in the rom of the MTZ act 2 sprite locations.

Also notice those 5552 values in there? Well those are for the unused level values in the game. You'll see some damn weird values put in for them in many places, and that's what causes the game to lockup in the final build of sonic 2 if you try and enter one of those levels.

There are other forms of an offset index such as the one where there's just one offset per level value, and another type that actually uses a double offset index. The first is easy enough, but a double offset index will specify two values per level, but that's not for act one and two, but rather two blocks of data to use for both acts.

Main level load block

This pointer table is what is used to load up the block mappings and main level patterns for every level in the game. Here's a breakdown of the pointer table in the S2B rom:

24354-2441F: Indexed main level load block (patterns/16x16/128x128)
24354-2435F: Emerald Hill zone (00)

24354: EHZ/HTZ main level patterns (81C00) [04]
24358: EHZ/HTZ 16x16 block mappings (80C60) [05]

2435C: EHZ/HTZ 128x128 block mappings (8692E) [04]
24360-2436B: Unknown (01)

24360: EHZ/HTZ main level patterns (81C00) [06]
24364: EHZ/HTZ 16x16 block mappings (80C60) [07]

24368: EHZ/HTZ 128x128 block mappings (8692E) [05]
2436C-24377: Wood zone (02)

2436C: WZ main level patterns (8AB2E) [08]
24370: WZ 16x16 block mappings (89B8E) [09]

24374: WZ 128x128 block mappings (9E926) [06]
24378-24383: Unknown (03)

24378: EHZ/HTZ main level patterns (81C00) [0A]
2437C: EHZ/HTZ 16x16 block mappings (80C60) [0B]

24380: EHZ/HTZ 128x128 block mappings (8692E) [07]
24384-2438F: Metropolis zone (04)

42384: MTZ main level patterns (91716) [0C]
42388: MTZ 16x16 block mappings (90456) [0D]

4238C: MTZ 128x128 block mappings (94C56) [08]
24390-2439B: Metropolis zone act 3 (05)

24390: MTZ main level patterns (91716) [0C]
24394: MTZ 16x16 block mappings (90456) [0D]

24398: MTZ 128x128 block mappings (94C56) [08]
2439C-243A7: Unknown (06)

2439C: EHZ/HTZ main level patterns (81C00) [10]
243A0: EHZ/HTZ 16x16 block mappings (80C60) [11]

243A4: EHZ/HTZ 128x128 block mappings (8692E) [0A]
243A8-243B3: Hill Top zone (07)

243A8: EHZ/HTZ main level patterns (81C00) [12]
243AC: EHZ/HTZ 16x16 block mappings (80C60) [13]

243B0: EHZ/HTZ 128x128 block mappings (8692E) [0B]
243B4-243BF: Hidden Palace zone (08)

243B4: HPZ main level patterns (98B76) [14]
243B8: HPZ 16x16 block mappings (97596) [15]

243BC: HPZ 128x128 block mappings (9B9F8) [0C]
243C0-243CB: Unknown (09)

243C0: EHZ/HTZ main level patterns (81C00) [16]
243C4: EHZ/HTZ 16x16 block mappings (80C60) [17]

243C8: EHZ/HTZ 128x128 block mappings (8692E) [0D]
243CC-243D7: Oil Ocean zone (0A)

243CC: OOZ main level patterns (9ED58) [18]
243D0: OOZ 16x16 block mappings (9D778) [19]

243D4: OOZ 128x128 block mappings (A1A58) [0E]
243D8-243E3: Dust Hill zone (0B)

243D8: DHZ main level patterns (A5248) [1A]
243DC: DHZ 16x16 block mappings (A3F88) [1B]

243E0: DHZ 128x128 block mappings (A8B6A) [0F]
243E4-243EF: Casino Night zone (0C)

243E4: CNZ main level patterns (ABF2A) [1C]
243E8: CNZ 16x16 block mappings (AB5CA) [1D]

243EC: CNZ 128x128 block mappings (AF026) [10]
243F0-243FB: Chemical Plant zone (0D)

243F0: CPZ main level patterns (B2506) [1E]
243F4: CPZ 16x16 block mappings (B0F26) [1F]

243F8: CPZ 128x128 block mappings (B6058) [11]
243FC-24407: Genocide City zone (0E)

243FC: EHZ/HTZ main level patterns (81C00) [20]
24400: EHZ/HTZ 16x16 block mappings (80C60) [21]

24404: EHZ/HTZ 128x128 block mappings (8692E) [12]
24408-24413: Aquatic Ruin zone (0F)

24408: ARZ main level patterns (B9E58) [22]
2440C: ARZ 16x16 block mappings (B8558) [23]

24410: ARZ 128x128 block mappings (BF568) [13]
24414-2431F: Death Egg zone (10)

24414: EHZ/HTZ main level patterns (81C00) [24]
24418: EHZ/HTZ 16x16 block mappings (80C60) [25]

2441C: EHZ/HTZ 128x128 block mappings (8692E) [14]

Now as you can see, these pointers specify the loading addresses in the rom for the 16x16 and 128x128 block mappings, as well as the main pattern block for that level. The main pattern block will always be loaded into the VRAM at address 0000. These loading addresses are all preceeded by a one byte value, so the address pointer only uses three bytes rather than the standard four. The value that proceeds the 128x128 block mappings specifies a value on the palette index to load for that level. For more information on the palette system, go <a href="#Palettes">here</a>. The values preceeding the main level pattern and 16x16 block mapping pointers give the index numbers of the pattern load cue's to use for that level. For more information on that go here.

Pattern load cue's

The pattern load cue's are what loads all the peices of art into the VRAM that are not in the main level load block. Here's a breakdown of the pattern load cue's in the S2B rom:

00 2447A Standard block 1 (starpoll/score\rings\time/lives/ring/numbers) (4)
01 2449A Standard block 2 (monitor/bubble/stars) (2)
02 244AE Unknown (explosion/rabbit/white bird) (2)
03 244C2 Game\time over (game\time over text) (0)
04 244CA EHZ (EHZ\HTZ patterns/waterfall/bridge/fireball/spikes/D spring/V spring/H spring) (7)
05 244FC EHZ (buzz bomber/tire badnick/fish) (2)
06 24510 WZ (WZ patterns) (0)
07 24518 WZ (spikes/D spring/V spring/H spring) (3)
08 24532 MTZ (MTZ patterns/4 blocks/wheel/ball/unknown/unknown/steam/spikeblock/spike) (8)
09 2456A MTZ (button/spikes/D spring/V spring/H spring/unknown/lava bubble/unknown/cog) (8)
0A 245A2 HTZ (EHZ\HTZ patterns/HTZ patterns/fireball/rock/conveyor/orbit badnick/spikes/D spring/V spring/H spring) (9)
0B 245E0 HTZ (unknown/fireball/HTZ barrier) (2)
0C 245F4 HPZ (HPZ patterns/bridge/waterfall/platform/pulsing ball/HPZ stuff/master emerald/water) (7)
0D 24626 HPZ (dinosaur badnick/bat/crocodile/buzz bomber/bat/rhinobot/dinosaur badnick/pirahna) (1)[7]
0E 24658 OOZ (OOZ patterns/rising platform/spikeball/stuff/stuff/oil/oil) (6)
0F 24684 OOZ (unknown/unknown/unknown/unknown/swinging platform/button/spikes/D spring/V spring/H spring/) (9)
10 246C2 MCZ (MCZ patterns/box/collapsing platform/pullswitch/vines) (4)
11 246E2 MCZ (H spike/spikes/log/lever spring/V spring/H spring) (5)
12 24708 CNZ (CNZ patterns/stuff) (1)
13 24716 CNZ (spikes/D spring/V spring/H spring) (3)
14 24730 CPZ (CPZ patterns/stuff/striped blocks/unknown/big platform/small platform/spring stopper/water/unknown/stuff) (9)
15 2476E CPZ (bubbles\numbers/spikes/unknown/level spring/V spring/ H spring) (5)
16 24794 ARZ (ARZ patterns/water/leaves/arrow shooter/splash) (4)
17 247B4 ARZ (bubbles\numbers/spikes/lever spring/V spring/H spring) (4)
18 247D4 Title card (title card patterns) (0)
19 247DC End of signpost level (signpost/hidden bonuses/unknown) (0)[2]
1A 247F0 End of boss level (unknown boss/EHZ boss/unknown/unknown boss/unknown boss/small explosion/smoke trail/EHZ boss/unknown) (2)[8]


This pointer list has an offset index to locate the correct cue. Go here for an explanation of how this works. Note that the number in parenthesis is the recorded number of requests in the cue. If a number follows it in brackets, it means the actual number that exists differs from the recorded one. This means any load requests past the recorded number were not being loaded, but still exist in the rom. Now, each load cue has a two byte value before it that specifies how many addresses are in the cue, to avoid it reading too far, and going into the next cue. This value is dead simple, just enter the number of patterns on the cue in hex between the first two bytes, but you have to count 00 as 1, so if there was 16 loading addresses in the cue, you'd have 000F preceding it. After that, there are 6 bytes per load request. The first four bytes are a pointer to the art block to use, and the two bytes after that are the location in the VRAM to load them into. To change the pattern load cue's being loaded for a level, you need to change the values in the main level load block. For more information on that go here.

Collision definitions

Ok, I’m going to explain how collision works on objects that are not sprites in the sonic games. First of all forget the image that the block contains. The image has absolutely nothing to do with the collision. There's basically in invisible collision box on top of every 16x16 block that sets what's solid and what's not. This collision box has two parts to it. The main part of it is the collision array (an array is basically a table of values). The collision array stores the actual data that says that is a block is solid in certain places. It does that through 16 bytes per collision box. To understand how those 16 bytes set what's solid, imagine a 16x16 block. Now imagine that 16x16 block with the numbers 1-10 (hex) down the side starting from the bottom and going up to the top, and starting from the left and going up as it moves right along the top, so that you can give an exact location of each pixel. (eg, the top left pixel would be 10,00) Now, in this array the first two bytes define what's solid for the row of pixels on the left side of that 16x16 block. Basically the first of those two bytes says where to start making things solid, and the second byte says where to stop making them solid. So if you entered the value 0010, the first row would be solid from the very bottom of the block all the way up to the top. If you were to enter the value 020E, there would be two pixels on either side of the block that are not solid, and everything in the middle would be. The next two bytes after that are for the next row, etc. After 16 bytes the definitions for the next collision box begin.

Now, to specify which blocks use which collision boxes, there are collision indexes, which give an array location for each 16x16 block. If you look at the space used by the collision array, you can divide that by 16 (the number of bytes used by each entry into the array) to give a one byte value, which represents the maximum number of collision boxes that the array can hold in the S2 platform, which is FF. Now, for each level there is at least one 16x16 collision index, and that index consists of a whole heap of array locations, one for each 16x16 block. If for example you wanted the 9th 16x16 block to use the collision box with an array location of 3E, you would give the 9th byte of the collision index for that level a value of 3E.

It is through collision indexes that the loops work in the game. It's commonly believed that there are layers, and that the sprite represented by 4 rings changes between them. This is partly true. For any levels that use multiple layers like that, there is a secondary 16x16 collision index. That object switches the 16x16 collision index in use. The pointers to these 16x16 collision indexes are stored at 4ADC-4B63. The first set of pointers in this group specify the location of the primary collision index to use for each level, and the second set specify the location of the secondary collision index to use for each level.

Now just setting something as solid, doesn't give it the effect of having a slope. There's an index in the rom, which has one byte in it for each collision array location. To understand how this value works, think of two lines running parallel to each other, both with the value 0-F along them. Now, the first value of the byte gives a point on the right line, and the second value gives a point on the left line. Now imagine drawing a line between these to points. If the points are different, the resulting gradient will be taken to create the effect of a slope and the resistance going up it on the box in the corresponding collision array location.

Level layout

The level layout in S2B is stored in the rom in a way similar to how the level layout is stored in the ram in S3&K. All the level data for a level is broken into two peices, one for the foreground of the level, and one for the background. When being read into the ram, this data is interleaved to give the entire level layout. The offset index that proceeds the actual level data is a unique offset index, and is similar to a double offset index. There are two offset values for each act. The first offset is linking to the data for the foreground for that act, and the second offset is linking to the background for that act. The level data itself is not compressed however, so you can just edit it directly. For information on how to edit it, check the savestate section.

Ring placement

The data for ring placement has an offset index to locate the correct group. Go here for an explanation of how this works. Now, in the rom each ring does not have to be stored individually. Instead you can place one ring, and specify that a certain number of rings come after it. The definitions for one ring takes up 4 bytes in the rom. Let's look at an example:

1234 5678
Now, in this example the ring will be placed at an x location of 1234, and a y location of 678. With that value where the 5 was entered, if the value entered is below 8, an additional ring will be placed next to the one before it for every unit that the value entered is above 0. Entering a value above 8 will place an additional ring below the one before it for each unit that the value entered is above 8. When specifying a position as the start of a group of rings, if the group is horizontal, the rings will go across to the right of that point, and if the group is vertical the rings will go down from that point. The value FFFF closes the group of ring locations, and it is essential that this is at the end of the ring locations list, or else the game will keep on reading past that point until it hits that value.

Sprite placement

Sprites are quite simple to define. It takes six bytes to define one sprite. The first two bytes are the x location of the sprite, and the next two bytes are the y location of the sprite. The 5th byte is the number on the sprite array to lookup to get the location for the function to use for the programming of that sprite, and the 6th byte is an optional declaration to use with the function for that sprite. Go here for more info on what exactly that means, and a list of all the sprites in the S2B rom.

Main level block mappings

In the S2B rom, the 128x128 block mappings are compressed, but the 16x16 block mappings are not. This means you can edit the 16x16 block mappings directly, but the 128x128 block mappings must be decomporessed to be edited effectively. At this point in time, there is no untility that is capable of compressing data into the format used by 128x128 block mappings, so the only thing that's really possible for now is porting the block mappings from one level to another. For information on what the block mappings do, and how to edit them, check the savestate section.

Uncompressed art

Any art that needs to be updated on the fly will not be compressed in the rom. This is because the game can't work with compressed data, and needs to extract any data it wants to use to the ram. This decompression process takes a fair bit of computation, and because of that it wouldn't be possible to create the appearance of a smooth animation using compressed data. The same reason is true as to why any data that is not loaded into the ram will always be uncompressed, because otherwise they would have to load it into the ram just to read it.

Now, for example all of the blocks for Sonic and Tails are uncompressed, because they of course need to be updated quickly. You can use basically any editing utility to edit them, but you can only change what each block looks like through this. In order to edit what blocks are placed where in each of Sonic's animation frames, you need to edit the mappings for them, and for more information on that go here. Now in their uncompressed form, you can edit them just like you would in the VRAM, so for more information on that check the sonic 2 savestate breakdown.

Mappings for Sonic/Tails

What the mappings do is they tell the game what patterns to display, and where to put them for each of the frames that the sprite has. The mappings for most sprites are contained within their function (go here for more details), but with the Sonic and Tails sprites, to allow the programmers to add a new frame easily without having to recompile the function, and hence the whole game because of the size difference, they created a separate array containing the mapping data for each frame. I haven't examined this to see how it works yet, but when I do I’ll explain the format here.

Sega intro sound

The Sega intro sound is just an 16000HZ wav sound. Opening up the rom in any sound editing program that supports raw audio with the settings listed next to the location on the list will enable you to playback the sound effect. You could also insert your own sound in the same place as long as it's at the same bitrate. The bitrate is to do with the quality of the sound. The lower it is the crappier it will sound, because that's to do with how often the output is modified. Just think of the difference between long play and short play on a VCR. Stuff recorded in long play does save space, but the quality of the recording is worse.

Art compression format

The art compression format is a very dense compression format. It's only used for art because the format relies on the data being in blocks of 64 bytes. This format is used for all the compressed art in sonic 1 and sonic 2 beta, and all the compressed art except for the main level pattern blocks in Sonic 2 and S3&K. As I said this format is very dense, and as such it requires a hell of a lot of computation to decompress. Because of this it also requires a hell of a lot of time and effort to crack. I've had a go at it, but the lightning has yet to strike. When I crack it I’ll post the format breakdown here, and create a simple program to decompress it, but until then it is impossible to directly edit any art using this format. The porting of a compressed block of art is simple though, so if you want to transfer beta art to the final, you can just tack it onto the end and enter the pointer into the pattern load cue of the level or event you want it to appear at, along with a VRAM location to load it into. Go Here for more information on that.

Dynamic pattern reloading

Dynamic pattern reloading is a method of loading patterns into the VRAM, but unlike the other methods, this one has no limitations, because it uses actual programmed code. Basically this is here for any effects to do with patterns changing in game that isn't posible using the normal load cue system, like the hills in the background of HTZ where the patterns to display are determined by the position of the screen Becuase the programming for it is in the form of compiled code, direct editing of it is not possible.

Animated pattern load cue's

Animated patterns require the art they are working with to be in an uncompressed form, so if you are attempting to make an animated pattern, make sure the art is uncompressed or it won't work. Now, the length of each load request on the cue varies depending on the animation. The first byte specifies a value that will determine how often to switch frames in the animation. If you use this value you will not be able to specify a frame as having a different duration to another. Setting this to FF will disable automatic frame control and allow the user to input a manual duration for each frame. This will mean that for every frame the user wants in the animation, they have to allow another byte at the end of the load request. If you want automatic pattern control, which you would use if you want all the animations frames to have the same duration. Just enter how many screen refreshes to wait until the next frame of the animation is displayed. Bytes 2,3, and 4 are the address in the rom to load the patterns from. Bytes 5 and 6 are the location in VRAM to load the patterns into. Byte 7 is the number of frames the animation has, and byte 8 is the number of spaces in VRAM to use for each frame. The function of the bytes beyond this point depend on whether or not automatic frame control is enabled, so refer to appropriate section below.

With automatic frame control:
One byte per frame of animation. This byte simply specifies the image to use for each frame of the animation. Based on the loading address entered, this value is the offset in 8x8 blocks to load each frame from in the rom. So if for example you were dealing with an animation that had 4 8x8 blocks per frame, and there were 4 frames of that, and you wanted it to display each frame one by one, you would enter the value 0004 080C.

Without automatic frame control:
Two bytes per frame of animation. The first byte is the offset of blocks in the file to load the animation frame from. This byte simply specifies the image to use for each frame of the animation. Based on the loading address entered, this value is the offset in 8x8 blocks to load each frame from in the rom. The second byte is the number of screen refreshes to keep that image loaded for, before going on to the next animation frame.

Misc sprite definitions

It looks like there are some sprites that get thier mappings and whatnot from this index, so they can reuse just a couple of sprites for some of the the miscellaneous objects in a level that the character doesn't actually interact with, but those objects can be completely different from one level to the next. A handy way of avioding programming each one individually, and thus saving a hell of a lot of space. As for how to edit them, well I haven't looked at that yet, but when I do i'll post an explination of the format here.

Rasterised layer deformation

Raster effects are simply effects to do with deformation of an image based on lines of pixels. In Sonic 2, these effects are used to create the movement effects for the backgrounds of all the levels, as well as the 2 player splitscreen effect. Because the programming for these effects are stored in the form of compiled code, you'll have to learn 68K ASM in order to edit them. Switching between levels is easy enough though, just change the corresponding value on the preceeding offset index to link to the effect you wish to use.

Palettes

All the main palettes used in the game are linked in a pointer table at 294E. In this pointer table there are 8 bytes per palette. The first four simply give a location in the rom for the data to load. The fifth and sixth bytes give the location in the system ram to load the data into, and the seventh and eighth bytes give the number of four byte blocks being loaded. Here's a palette pointer:

0000 2942 FB20 0007

Now in this case the palette is being loaded from 00002942 in the rom into the beginning of the second above water palette row (FB20), and it's loading 16 colours (0007). Here's a listing of the palette pointers in the S2B rom:

00 294E SEGA screen palette (2A16)
01 2956 Title screen palette (2A96)
02 295E Level select palette (2B16)
03 2966 Primary palette line (2B96)
04 296E EHZ level palette (2BB6)
05 2976 01 level palette (2BB6)
06 297E WZ level palette (2C16)
07 2986 03 level palette (2BB6)
08 298E MTZ level palette (2C76)
09 2996 05 level palette (2C76)
0A 299E 06 level palette (2F36)
0B 29A6 HTZ level palette (2CD6)
0C 29AE HPZ level palette (2D36)
0D 29B6 09 level palette (2BB6)
0E 29BE OOZ level palette (2E16)
0F 29C6 MCZ level palette (2E76)
10 29CE CNZ level palette (2ED6)
11 29D6 CPZ level palette (2F96)
12 29DE GCZ level palette (2BB6)
13 29E6 ARZ level palette (3076)
14 29EE DEZ level palette (2BB6)
15 29F6 HPZ underwater palette (2D96)
16 29FE CPZ underwater palette (2FF6)
17 2A06 ARZ underwater palette (30D6)
18 2A0E Sonic 1 special stage palette (3156)


To change the palette being loaded for each level, you need to change the palette index number in the main level load block. For more information on that go here. The palettes themeslves are very easy to modify as they are all uncompressed in the rom. Refer to the savestate hacking documents for information on how to edit palettes.

Level size array

All the sizes of the levels are stored in a simple array, and can be easily modified to change the boundaries of the level. This array is located at 5986, and for each act there are four values. The first gives the X start location of the level, and the second gives the X end location of the level. Likewise the third value gives the Y start location of the level, and the fourth gives the Y end location of the level.

Character start location array

The start location for the characers and the camera for each level are stored in this array at address 5B02. It couldn't be any simpler to modify, there's just two values per act, the first being the X location, and the second being the Y location.

Music playlist for levels

This is actually part of a sub in the code, but it's editable all the same. Pretty simple, just one byte per level. That one byte is the value of the song you wish to play. You must enter the value in the form in which it is displayed in the beta version, which is with 80 as the starting value, not 00 as it is displayed in the final. You'll notice with the value for death egg, it's 08 not 88, which is why there's no sound in the level.

Level order

There are several different sections in the game to do with the order of levels. The first one is the one that determins which level the game loads when someone finishes a level. The second one is the one which determins which level to load when you select a level from the level select menu. The level select one is easy to modify, just enter the level value followed by an act number for each of the levels you want to load, in the order you want them to be loaded. For a list of the level values for all the different stages, look at the beginning of the introduction to this page. Note that if you load the same level into the level order twice, when you link to it via the level select, it will continue the sequence from the last one in the list, not the first.

The second system for which level to load when one ends works slightly differently. There is a list of values, with two bytes allocated to each act of each level. That two byte value is simply the value of the level you wish to load when that level ends. So, if you wanted ARZ act 1 to load up when you finish MTZ act 2, you would take the location of the table, which in this case is BF9A, and you would add 18 bytes to that location, and then you would replace the next two bytes from that point with 0F00. That's becuase you add four bytes to the address for every level that comes before it, and in this case there are 4, and then you would add another 2 bytes becuase you want to alter the level to load when you finish the second act.

Also, note that when you want a level to be the last level in the game, you must enter the value FFFF as the stage to load when it finishes. This tells the game to end and return to the title screen.

Object debug list

This list is what determins what sprites you can place in debug mode, and in what levels. An offset index is used to locate which object debug list to use for which level, so if you want further info on that go <a href="#offset">here</a>. Now, there is a 2 byte value at the start of each debug list. That 2 byte value is simply the number of sprites in the list. After that there are 8 bytes per sprite. Here's an object that's present in an object debug list from sonic 2:

2601 2D36 0800 0680
1 2 3 4 5 6 7 8


And here's a quick referance sheet of what each byte does. For further info on each one, refer to information below.

1 Object number
2-4 Sprite mappings
5 Declaration
6 Frame to display
7 and 8 flip/mirror/palette/VRAM location


Object number:
This value is what determins which object to use. For a list of all the sprites in the game, check out the sprite programming section of this document here. In the case of the above example the object number is 26, which is a monitor.

Sprite mappings:
This is a pointer to the location in the rom to load the mappings for that sprite. This will be located in the programming for the sprite itself. Do not change this unless porting between levels, or you're absolutely sure you know what you're doing, or the game will most likely hang. This only affects the preview picture, not the placed object itself. In this case, the sprite mappings are being loaded from the address 012D36 in the rom.

Declaration:
This is the declaration for the loading of the sprite. For information on exactly what that is, go here. In this example the declaration is 08, which switches the type of monitor it is in the case of this sprite.

Frame to display:
This is simply the frame of the sprite that will be displayed on the preview picture before you place an object. Right now it's set to 00, which is the first frame.

Flip/mirror/VRAM location:
The first hex value of the 7th byte is to do with flipping and mirroring of the sprite, as well as the palette line to use for it. Refer to the following table for an explination of what responce each value will create.

Value palette line flipped horizntally flipped vertically
0 1 n n
1 1 n y
2 2 n n
3 2 n y
4 3 n n
5 3 n y
6 4 n n
7 4 n y
8 1 n n
9 1 y n
A 2 n n
B 2 y n
C 3 n n
D 3 y n
E 4 n n
F 4 y n

In the case of our example, the value of 0 is used, so the preview image will use the first palette line, and will not be flipped or mirrored.

The last hex value of the 7th byte, and all of the 8th byte in this block combine to give a starting location in the VRAM to find the patterns to use for that sprite when displaying the preview. This is not an actual location, but merely the number of blocks after which to load the patterns from. After the value of 800 is passed, the block number resets to zero but the image is mirrored. In this case, that block number is 680.

And that's about it. I've just realised that this is a rediculous amount of detail for such a small thing, but at least you're sure to get it.

Leftover data from previous builds

All through the S2B rom, there are blocks of leftover data from earlier builds of the game. You see, when sonic team were working on the game, they would compile beta versions of the game onto flashcarts, for test purposes and distribution. Because the data was compiled directly onto the cart, any locations that didn't have to be written to retained the data they posessed before. On a final release cart, this simply would've resuled in blocks of data all contaning the value of FF, but in the case of this flashcart, data for earlier versions of the game had been written to these areas previously. Any areas of lost data that I have extra information about will be noted here.

End of compressed ARZ 128x128 block mappings

This small reminant of a rather recent build indicates a minor change in the above blocks of data, which resulted in a slightly shorter file size. This was most likely just a minor amendment to the block mappings for a level, resulting in them not compressing quite as well.

large chunk of CNZ 128x128 block mappings

This contains a large proportion of an earlier version of the CNZ 128x128 block mappings. The block of data is missing the first 3340 (D0C) bytes. From this we can see a massive chanage in CNZ between this compilation and the one in our beta. These block mappings have been changed so radically, that only a pattern in thier layout is recogniseable when compared to our current beta one. This indicates a massive restructuring in the order of the 16x16 block mappings of this build as well, but unfortunately that data was written over.

CPZ patterns/block mappings

These are the complete patterns and block mappings for an earlier version of CPZ. There are a few minor changes in the patterns, and some fairly major changes in the 16x16 and 128x128 block mappings.

Compressed ARZ 128x128 block mappings

This lost data is in an uncompiled form, and at first I mistook it for code. Apart from the fact it is in this form, the data appears to be very close to that of our current beta. There is a commented line at the very start of the block, which contains further information about the block of compressed data. Thanks go out to Iceknight, who figured out that the text in this comment was in Kanji, and thanks go out to Kojichao and sth2k for translating it. The commented line reads:

Before compression $8000 After compression $2c00 Compression ratio 34.4% Cell number 1024

I had already guessed the purpose of the first three numbers, But I still can't figure out the puropse of the last one, or at least not one that would be worth putting in a comment. If anyone has any idea what the fourth number is used for, let me know.

lost Pattern load cue's

Due to changes in the structure of the rom, there are quite a few pattern load cue's left from previous compilations. In fact, in this one small area in the rom, I have identified six different layers of lost data from previous compilations, and these compilations seem to be a lot newer than the remains of level data judging by some of the link locations on the cue. Here's a breakdown of the lost pattern load cue's:

24804 End of boss level (unknown boss/unknown boss/small explosion/smoke trail/EHZ boss/unknown) (?)[5]
24828 ARZ (lever spring/V spring/H spring) (?)[1/2+1]
24838 Title card (title card patterns) (0)
24840 End of signpost level (signpost/hidden bonuses/unknown) (0)[2]
24854 End of boss level (unknown boss/EHZ boss/unknown/unknown boss/unknown boss/small explosion/smoke trail/EHZ boss/unknown/) (2)[8]
2488C End of boss level (smoke trail/EHZ boss/unknown) (?)[1/2+1]
2489C MCZ (log/invalid pointer (7976C)/V spring/H spring) (?)[3]
248B4 CNZ (invalid pointer (AB748)/invalid pointer (AE75A)) (1)
248C2 CNZ (spikes/D spring/V spring/H spring) (3)
248DC CPZ (invalid pointer (B1D24)/stuff/striped blocks/unknown/big platform/small platform/spring stopper/water/unknown/stuff) (9)
2491A CPZ (spikes/unknown/invalid pointer (7976C)/V spring/H spring) (4)
2493A ARZ (invalid pointer (B9686)/water/leaves/arrow shooter/splash) (4)
2495A ARZ (spikes/invalid pointer (7976C)/V spring/H spring) (3)
24974 Title card (invalid pointer (7E222)) (0)
2497C End of signpost level (signpost/invalid pointer (7F37A)/invalid pointer (7F206)) (2)
24990 End of boss level (invalid pointer (7C4BC)/invalid pointer (7D942)/invalid pointer (7E12E)/invalid pointer (7C4BC)/invalid pointer (7CBF8)/invalid pointer (7D7DE)/invalid pointer (7D85C)/invalid pointer (7D942)/invalid pointer (7E12E)) (2)[8]
249C8 ARZ (invalid pointer (?AD00)/invalid pointer (7976C)/V spring/H spring) (?)[1/2+2]
249DC Title card (invalid pointer (7E222)) (0)
249E4 End of signpost level (signpost/invalid pointer (7F37A)/invalid pointer (7F206)) (2)
249F8 End of boss level (invalid pointer (7C4BC)/invalid pointer (7D924)/invalid pointer (7E12E)/invalid pointer (7C4BC)/invalid pointer (7CBF8)/invalid pointer (7D7DE)/invalid pointer (7D85C)/invalid pointer (7D942)/invalid pointer (7E12E)) (2)[8]


If you want more info on the pattern load cue's, go here. From these load cue's we can see that there were some changes in the locations of some of the small blocks of compressed art, and that has resulted in some of the older pointers linking to the wrong data. The thing that I find most interesting about this deals with the load cue for the end of signpost level load cue. You'll notice with this cue that the last two load requests were cutoff in our beta, which link to those hidden bonues at the end of an act in Sonic 1, and more importantly, the flash effect from entering the giant golden ring, that leads to a special stage. The patterns for this ring are in the rom, but until I saw this I wasn't convinced that it was ever implemented in the game. Now, if you look at the cue that's colour coded yellow, you'll notice it isn't cutoff yet, but in the green compilation it has been, so somewhere between those two compilations, the ideas they were using for the method of entering the special stage, and the bonus points at the end of a level were changed. If you compare the link locations of the main level patterns for any of the levels in the yellow load cue's with the current link locations, and the lost block mappings and art there, it's clear that all these cue's are for compilations made after the compression methods for both 16x16 and 128x128 block mappings were put in place, which either means that those blocks of data with the block mappings and level patterns are from a much earlier compilation than I figured, or the ideas for the end of a level were changed just before the time of our beta.

Sprite programming

The programming for a sprite in the sonic games are stored as a function, and that function can take one declaration. People often confuse this declaration with a subtype value, but it's not really. What that basically means for the non programmers out there is that when the game places a sprite, you can enter a value along with the sprite number that may alter something about that sprite, but what it does varies depending on what sprite you're working with. Now because these functions are now compiled, the only way you can effectively edit them is to find the code for it and decompile it into assembly, alter it as necessary, and then recompile it and enter it back into the rom. This document will contain all the info necessary to enter a new sprite or replace an old one, but when it comes to the ASM you're on your own.<p>

Now, the value assigned to a sprite in the game is done by a pointer index at D01A-D249. It’s pretty simple, just one pointer per address value. Here's the pointer list in Sonic 2 beta:

01 Sonic [FC48]
02 Tails [10E38]
03 Collision index switcher [144B0]
04 ??????? [15090]
05 Tails' tail [11F96]
06 Spiral loop in EHZ [1572C]
07 ??????? [180D0]
08 ??????? [12B42]
09 Sonic from S1 special stage [21D40]
0A Flashing number that gives air countdown [1207C]
0B Block that tips you off from CPZ [148AC]
0C Unknown (A small one way block. At set intervals the platform raises slightly then goes back down. Movement is slow and erattic, not smooth.) [149FC]
0D Signpost [F1F4]
0E Unknown (a huge block locked onscreen) [B7B4]
0F Unknown (very very weird. Using the blocks for a computer, every time you press jump another block for it appears locked onscreen int he top left corner) [B83A]
10 ??????? [223E2]
11 Bridge [7FDC]
12 The master emerald [14AFC]
13 Waterfall from HPZ [14B78]
14 See-saw [15B8C]
15 Unknown (crashes emulator) [85F8]
16 Diagnally moving and falling platform from HTZ [1600C]
17 Ball badnick from CPZ that goes up one tube and down another [8B9C]
18 Fixed large platform from CPZ [8D38]
19 Large platform from CPZ moving from side to side [1621C]
1A Collapsing platform from OOZ [9128]
1B Boosters from CPZ [16468]
1C ??????? [999C]
1D Enemy made up of small blue balls in CPZ [165B0]
1E Spin-tube from CPZ [16724]
1F Breakaway platform made up of small blocks from MZ in S1 [9274]
20 Unknown (An invincible object that drops two fireballs at a time, one on either side. object is fixed and cannot be hurt.) [17174]
21 Onscreen display (lives/score/time/rings) [22DFC]
22 Arrow shooter from ARZ [19660]
23 Piller that drops lower half in ARZ [19850]
24 Unknown (sprite cycles frames and then disappears) [A012]
25 Ring [AC28]
26 Monitor [B29C]
27 Explosion giving off 100 points and an animal [A086]
28 Unknown (some weird thing using some scrambled animal patterns bouncing up and down) [A2B0]
29 100 points [A7C0]
2A Stomper from MCZ [9C0C]
2B Raising pillar from ARZ [19A1E]
2C Leaves from ARZ [1A0C4]
2D One way barrier from ARZ [9CE2]
2E Contents of computer monitor flying up [B46A]
2F Unknown (suspect it's the blocks you bust blocking the loops in HTZ) [1747C]
30 Unknown (a collision box the size of the screen) [17A4C]
31 Boundary block for lava [155A0]
32 Cap on top of spin tubes in CPZ [1768A]
33 Platform on top of oil burners from OOZ [17CA0]
34 ??????? [BB54]
35 ??????? [1264E]
36 Spikes [C944]
37 Ring spray [AD62]
38 ??????? [125CE]
39 Game over text [BD76]
3A End of act sprite (ends level) [BE38]
3B Unknown (a block) [CD00]
3C Bustable vertical barrier [CD7C]
3D Block that propells sonic when he busts it from OOZ [18E78]
3E Unknown (a block) [20E5C]
3F Red explosion [A11E]
40 Weird spring from ARZ and CPZ [1A30C]
41 Horizontal red spring [E7B8]
42 Steam vent from MTZ [1A5CC]
43 Spikeball from OOZ [17F0C]
44 Unknown (a vertical barrier) [F10C]
45 Weird spring that you push back on from OOZ [181A0]
46 Ball on weird spring from OOZ [18ABE]
47 Button [18D9C]
48 Spinball that shoots character out 90 degrees from entry from OOZ [19250]
49 Waterfall in EHZ [15352]
4A Octopus badnick from OOZ [1EBB8]
4B Buzz bomber [1E89C]
4C Bat [1EE68]
4D Rhinobot [1D984]
4E Alligator [1F2F0]
4F Dinobot [1DEAC]
50 Unknown badnick (rapidly changes direction in the air) [1E010]
51 Unknown badnick (Almost identical to above, but periodically shoots something to the left.) [1E62C]
52 Pirhana [1DC54]
53 Jumping fish from EHZ [1F5E8]
54 Land based driving badnick from EHZ [1F6E8]
55 Robotnic in his main ship [2030C]
56 Unknown (scrolls patterns then disappears. possibly new explosion effect) [205A6]
57 ??????? [1F99C]
58 EHZ boss [1FC0A]
59 ??????? [D24A]
5A ??????? [D24A]
5B ??????? [D24A]
5C ??????? [D24A]
5D ??????? [D24A]
5E ??????? [D24A]
5F ??????? [D24A]
60 ??????? [D24A]
61 ??????? [D24A]
62 ??????? [D24A]
63 ??????? [D24A]
64 Stompers from MTZ [1A8B4]
65 Unknown (a horizntal block) [1AA74]
66 Bouncers from MTZ [1AEBC]
67 Warp tube from MTZ [1B0C4]
68 Block in MTZ with a spike coming out each side sequentially [1B520]
69 Nut that character moves by running on in MTZ [1B810]
6A Unknown (a platform that moves when you jump off it) [1BA30]
6B Unknown (Same as above, but not moving) [1BCEC]
6C ??????? [1BF6C]
6D Floor spike in MTZ [1B720]
6E Platform moving in circle [1C2E4]
6F Diagnally moving platform from MTZ [1C4F8]
70 8 points on giant cog from MTZ [1C850]
71 Pulsing ball in HPZ [9A54]
72 ??????? [1CBCC]
73 Unknown (sprite has the image of a fixed ring. Sprite acts as a barrier if collision occurs) [1CC54]
74 Unknown (a block with no image) [1561A]
75 ??????? [1CE48]
76 Moving spikey arm from MCZ [1D078]
77 Unknown (if character hits sprite it turns into a vertical barrier that then opens up, and immediately after makes emulator freeze.) [1D208]
78 Lowering stairs from CPZ [1D3C0]
79 Starpoll [13B54]
7A Small yellow moving platform from CPZ [1D594]
7B Spring on spin tube cap from CPZ [1D74C]
7C ??????? [D24A]
7D Unknown (if collision occurs, emulator freeses) [13DFC]
7E ??????? [D24A]
7F ??????? [D24A]
80 ??????? [D24A]
81 ??????? [D24A]
82 ??????? [D24A]
83 ??????? [D24A]
84 ??????? [D24A]
85 ??????? [D24A]
86 ??????? [D24A]
87 ??????? [D24A]
88 ??????? [D24A]
89 ??????? [D24A]
8A Unknown (some kind of single lined text on screen) [20740]
8B ??????? [D24A]
8C ??????? [D24A]
Sonic Community Hacking Guide
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