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SCHG How-to

Improve ObjectMove subroutines

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Revision as of 02:58, 28 June 2012 by KingofHarts (talk | contribs) (Was an optional step in one of RHS' guides, but that guide was already 12 steps... so I made this its own guide.)
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(Guide written by redhotsonic)

Want to speed up your Sonic 2 hack?

In S2 and S3K, there's a subroutine called "ObjectMove" and another subroutine called "ObjectMoveandFall". ObjectMove allows objects to move about and "ObjectMoveandFall" does the same, except it applies gravity to it.

S3K has the same subroutines except the code is a bit shorter and therefore, it's faster. It may not look much faster, but again, with all the objects on screen, it has to apply it for every frame.

So, let's change our routines to work more like S3K's. To do this, it's really simple.

Go to "ObjectMoveAndFall:" and change this: <asm> ObjectMoveAndFall: 

       move.l  x_pos(a0),d2    ; load x position
       move.l  y_pos(a0),d3    ; load y position
       move.w  x_vel(a0),d0    ; load x speed
       ext.l   d0
       asl.l   #8,d0   ; shift velocity to line up with the middle 16 bits of the 32-bit position
       add.l   d0,d2   ; add x speed to x position     ; note this affects the subpixel position objoff_A(a0) = 2+x_pos(a0)
       move.w  y_vel(a0),d0    ; load y speed
       addi.w  #$38,y_vel(a0)  ; increase vertical speed (apply gravity)
       ext.l   d0
       asl.l   #8,d0   ; shift velocity to line up with the middle 16 bits of the 32-bit position
       add.l   d0,d3   ; add old y speed to y position ; note this affects the subpixel position objoff_E(a0) = 2+y_pos(a0)
       move.l  d2,x_pos(a0)    ; store new x position
       move.l  d3,y_pos(a0)    ; store new y position
       rts
End of function ObjectMoveAndFall

</asm>

To this: <asm> ObjectMoveAndFall: 

       move.w  x_vel(a0),d0
       ext.l   d0
       lsl.l   #8,d0
       add.l   d0,x_pos(a0)
       move.w  y_vel(a0),d0
       addi.w  #$38,y_vel(a0) ; apply gravity
       ext.l   d0
       lsl.l   #8,d0
       add.l   d0,y_pos(a0)
       rts
End of function ObjectMoveAndFall

</asm>

Next, go to "ObjectMove:" and change this: <asm> ObjectMove: 

       move.l  x_pos(a0),d2    ; load x position
       move.l  y_pos(a0),d3    ; load y position
       move.w  x_vel(a0),d0    ; load horizontal speed
       ext.l   d0
       asl.l   #8,d0   ; shift velocity to line up with the middle 16 bits of the 32-bit position
       add.l   d0,d2   ; add to x-axis position        ; note this affects the subpixel position objoff_A(a0) = 2+x_pos(a0)
       move.w  y_vel(a0),d0    ; load vertical speed
       ext.l   d0
       asl.l   #8,d0   ; shift velocity to line up with the middle 16 bits of the 32-bit position
       add.l   d0,d3   ; add to y-axis position        ; note this affects the subpixel position objoff_E(a0) = 2+y_pos(a0)
       move.l  d2,x_pos(a0)    ; update x-axis position
       move.l  d3,y_pos(a0)    ; update y-axis position
       rts
End of function ObjectMove

</asm>

to this: <asm> ObjectMove: 

       move.w  x_vel(a0),d0
       ext.l   d0
       lsl.l   #8,d0
       add.l   d0,x_pos(a0)
       move.w  y_vel(a0),d0
       ext.l   d0
       lsl.l   #8,d0
       add.l   d0,y_pos(a0)
       rts
End of function ObjectMove

</asm>

That's that. For any object that has to move, it will now do this coding a lot quicker each frame.

SCHG How-To Guide: Sonic the Hedgehog 2 (16-bit)
Fixing Bugs
Fix Demo Playback | Fix a Race Condition with Pattern Load Cues | Fix Super Sonic Bugs | Use Correct Height When Roll Jumping | Fix Jump Height Bug When Exiting Water | Fix Screen Boundary Spin Dash Bug | Correct Drowning Bugs | Fix Camera Y Position for Tails | Fix Tails Subanimation Error | Fix Tails' Respawn Speeds | Fix Accidental Deletion of Scattered Rings | Fix Ring Timers | Fix Rexon Crash | Fix Monitor Collision Bug | Fix EHZ Deformation Bug | Correct CPZ Boss Attack Behavior | Fix Bug in ARZ Boss Arrow's Platform Behavior | Fix ARZ Boss Walking on Air Glitch | Fix ARZ Boss Sprite Behavior | Fix Multiple CNZ Boss Bugs | Fix HTZ Background Scrolling Mountains | Fix OOZ Launcher Speed Up Glitch | Fix DEZ Giant Mech Collision Glitch | Fix Boss Deconstruction Behavior | Fix Speed Bugs | Fix 14 Continues Cheat | Fix Debug Mode Crash | Fix 99+ Lives | Fix Sonic 2's Sega Screen
Design Choices
Remove the Air Speed Cap | Disable Floor Collision While Dying | Modify Super Sonic Transformation Methods & Behavior | Enable/Disable Tails in Certain Levels | Collide with Water After Being Hurt | Retain Rings When Returning at a Star Post | Improve the Fade In\Fade Out Progression Routines | Fix Scattered Rings' Underwater Physics | Insert LZ Water Ripple Effect | Restore Lost CPZ Boss Feature | Prevent SCZ Tornado Spin Dash Death | Improve ObjectMove Subroutines | Port S3K Rings Manager | Port S3K Object Manager | Port S3K Priority Manager | Edit Level Order with ASM‎ | Alter Ring Requirements in Special Stages | Make Special Stage Characters Use Normal DPLCs | Speed Up Ring Loss Process | Change spike behaviour in Sonic 2
Adding Features
Create Insta-kill and High Jump Monitors | Create Clone and Special Stage Monitors | Port Knuckles
Sound Features
Expand Music Index to Start at $00 | Port Sonic 1 Sound Driver | Port Sonic 2 Clone Driver | Port Sonic 3 Sound Driver | Port Flamewing's Sonic 3 & Knuckles Sound Driver | Expand the Music Index to Start at $00 (Sonic 2 Clone Driver Version) | Play Different Songs Per Act
Extending the Game
Extend the Level Index Past $10 | Extend the Level Select | Extend Water Tables | Add Extra Characters | Free Up 2 Universal SSTs
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