How to add Water Skimming

How to add Water Skimming in Sonic 1


Water skimming was first seen in Sonic 2 for SMS, it also appeared in Sonic 3 for SMD, but worked a little different. Due to LZ levels in Sonic 1 aren't designed for fast walkthrough, 8-bit Sonic 2 Water Skimming would suit better. So it will work this way:





Adding this ability is quite easy.


Find Obj_MdJump2 label, so you'll see something like this:



Obj01_MdJump2: ; XREF: Obj01_Modes
bsr.w Sonic_JumpHeight


bsr.w Sonic_ChgJumpDir


bsr.w Sonic_LevelBound


jsr ObjectFall


btst #6,$22(a0)


beq.s loc_12EA6


subi.w #$28,$12(a0)



Append it with the following code:



move.w $10(a0),d0 ; move Sonic's X-velocity to d0
tst.w d0 ; is his speed positive? (is he running to the right?)


bpl.s Obj01_MdJump2_Abs ; if yes, branch


neg.w d0 ; otherwise negate it


Obj01_MdJump2_Abs:


cmpi.w #$250,d0 ; if Sonic speed less than $250?


blt.s loc_12EA6 ; if yes, branch


move.w $C(a0),d0 ; move sonic's Y-position to d0


sub.w ($FFFFF646).w,d0 ; sub the water height from it


cmpi.w #$F,d0 ; is Sonic slightly in the water?


bgt.s loc_12EA6 ; if not, branch


subi.w #$90,$12(a0) ; jump out of water



That's all. Build your ROM and try new ability!


Please correct me if you've noticed grammar or lexical mistakes in this text.

 

For someone who says he knows ASM bad you are pretty good at it.



move.w $10(a0),d0 ; move Sonic's X-velocity to d0
tst.w d0 ; is his speed positive? (is he running to the right?)


bpl.s Obj01_MdJump2_Abs ; if yes, branch


neg.w d0 ; otherwise negate it


Obj01_MdJump2_Abs:


cmpi.w #$250,d0 ; if Sonic speed less than $250?


blt.s loc_12EA6 ; if yes, branch


move.w $C(a0),d0 ; move sonic's Y-position to d0


sub.w ($FFFFF646).w,d0 ; sub the water height from it


cmpi.w #$F,d0 ; is Sonic slightly in the water?


bgt.s loc_12EA6 ; if not, branch


subi.w #$90,$12(a0) ; jump out of water



I was bored and commented it. =P

 

I forgot to mention that my phrase "...I know ASM bad..." has expired already

Thanks for commenting.


I wanted to comment it too, but was too lazy. I've even forgotten to fix some bugs.

 

That's very impressive, I like the fact that you actually know how to program this stuff unlike everyone else on this damn forum, whom of which burst in here asking for help every 5 minutes.


Great work though, non the-less =)

 

Wait, shouldn't this be in Sourcecode exchange?

 

I believe not--this is a tutorial on how to add something.

 

Well actually it's both, tutorial and source code guide, because it's a 100% c/p guide, without explaining (except for the comments). There should be at least a link in the exchange forum.

 

EDIT: Remove this post please

 

If I may would I be able to change this line;


bpl.s Obj01_MdJump2_Abs ; if yes, branch


To this line;


bpl.s Sonic_Move ; if yes, branch


Would it work the same?

 

Don't ask, try it! It's so easy to check it out.


If this works as you planned, it will be a great discovery for the Sonic Hacking Community.