Difference between revisions of "Fix Scattered Rings Underwater Physics"
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This ensures when underwater, the gravity is not as great. Otherwise, the rings will gain speed and then it won't give the desired underwater effect. | This ensures when underwater, the gravity is not as great. Otherwise, the rings will gain speed and then it won't give the desired underwater effect. | ||
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| + | [[Category:SCHG How-tos|Fix Scattered Rings Underwater Physics]] | ||
Revision as of 09:43, 23 April 2012
(Guide for all 3 games written by redhotsonic.
Quote from redhotsonic, - "Ah, the scattered rings when you get hurt. It can cause slowdown to your game, and even mess up the underwater palette. Now, when Sonic is underwater, his movement and his gravity is changed so he moves slower to act like he's in water. But when he is hurt under water, isn't it funny that the scattered rings still act the same as if you weren't in water?"
This is something that occurs in all 3 Sonic the Hedgehog Mega Drive games (and by 3, that IS counting S3&K as one game, though S&K has no water anyway, so it wouldn't be included regardless... but I digress). But is it really a bug? or is it merely a design choice? In either case, it's something that could stand to be fixed, and this guide tells you how to fix the ring physics in all of the games. First off... let's start with the original...
Sonic 1 fix - This guide uses the SVN disassembly.
First, In your disassembly, go to "_incObj\25 & 37 Rings.asm" Go to @makerings: (part of the scattered rings object code) and find this bit of coding: <asm>
bsr.w CalcSine
move.w d4,d2
lsr.w #8,d2
</asm>
Just underneath, paste this: <asm>
tst.b ($FFFFF64C).w ; Does the level have water?
beq.s @skiphalvingvel ; If not, branch and skip underwater checks
move.w ($FFFFF646).w,d6 ; Move water level to d6
cmp.w y_pos(a0),d6 ; Is the ring object underneath the water level?
bgt.s @skiphalvingvel ; If not, branch and skip underwater commands
asr.w #$1,d0 ; Half d0. Makes the ring's x_vel bounce to the left/right slower
asr.w #$1,d1 ; Half d1. Makes the ring's y_vel bounce up/down slower
@skiphalvingvel: </asm>
'You should end up with something looking like this:' <asm> @makerings:
move.b #id_RingLoss,0(a1) ; load bouncing ring object
addq.b #2,obRoutine(a1)
move.b #8,obHeight(a1)
move.b #8,obWidth(a1)
move.w obX(a0),obX(a1)
move.w obY(a0),obY(a1)
move.l #Map_Ring,obMap(a1)
move.w #$27B2,obGfx(a1)
move.b #4,obRender(a1)
move.b #3,obPriority(a1)
move.b #$47,obColType(a1)
move.b #8,obActWid(a1)
move.b #-1,(v_ani3_time).w
tst.w d4
bmi.s @loc_9D62
move.w d4,d0
bsr.w CalcSine
move.w d4,d2
lsr.w #8,d2
tst.b ($FFFFF64C).w ; Does the level have water?
beq.s @skiphalvingvel ; If not, branch and skip underwater checks
move.w ($FFFFF646).w,d6 ; Move water level to d6
cmp.w y_pos(a0),d6 ; Is the ring object underneath the water level?
bgt.s @skiphalvingvel ; If not, branch and skip underwater commands
asr.w #$1,d0 ; Half d0. Makes the ring's x_vel bounce to the left/right slower
asr.w #$1,d1 ; Half d1. Makes the ring's y_vel bounce up/down slower
@skiphalvingvel:
asl.w d2,d0
asl.w d2,d1
move.w d0,d2
move.w d1,d3
addi.b #$10,d4
bcc.s @loc_9D62
subi.w #$80,d4
bcc.s @loc_9D62
move.w #$288,d4
</asm> This ensures that when underwater, the rings x_vel and y_vel are halved so they appear to be moving slower.
Next, go to label "RLoss_Bounce:" and under <asm>
move.b (v_ani3_frame).w,obFrame(a0)
bsr.w SpeedToPos
addi.w #$18,obVelY(a0)
</asm> place this: <asm>
tst.b ($FFFFF64C).w ; Does the level have water?
beq.s @skipbounceslow ; If not, branch and skip underwater checks
move.w ($FFFFF646).w,d6 ; Move water level to d6
cmp.w y_pos(a0),d6 ; Is the ring object underneath the water level?
bgt.s @skipbounceslow ; If not, branch and skip underwater commands
subi.w #$E,obVelY(a0) ; Reduce gravity by $E ($18-$E=$A), giving the underwater effect
@skipbounceslow: </asm> You can change the value of the gravity if you like, but I found $E to suit. Anyway, you should have something looking like this: <asm> RLoss_Bounce: ; Routine 2
move.b (v_ani3_frame).w,obFrame(a0)
bsr.w SpeedToPos
addi.w #$18,obVelY(a0)
tst.b ($FFFFF64C).w ; Does the level have water?
beq.s @skipbounceslow ; If not, branch and skip underwater checks
move.w ($FFFFF646).w,d6 ; Move water level to d6
cmp.w y_pos(a0),d6 ; Is the ring object underneath the water level?
bgt.s @skipbounceslow ; If not, branch and skip underwater commands
subi.w #$E,obVelY(a0) ; Reduce gravity by $E ($18-$E=$A), giving the underwater effect
@skipbounceslow:
bmi.s @chkdel
move.b (v_vbla_byte).w,d0
add.b d7,d0
andi.b #3,d0
bne.s @chkdel
jsr ObjFloorDist
tst.w d1
bpl.s @chkdel
add.w d1,obY(a0)
move.w obVelY(a0),d0
asr.w #2,d0
sub.w d0,obVelY(a0)
neg.w obVelY(a0)
</asm> This ensures when underwater, the gravity is not as great. Otherwise, the rings will gain speed and then it won't give the desired underwater effect.