SCHG How-to:Fix the HUD blinking

by Quickman

There's a bug in the HUD in Sonic 1 - the timer is supposed to blink if there's less than a minute left to go, which it does if you have no rings, but as soon as you collect a ring it stops blinking. That's silly, so let's fix it.

If you're using the SVN disassembly, open _incObj/21 HUD.asm. The older disassembly by Hivebrain has it as Obj21_Flash in the main sonic.asm file, and will have some labels different, but I assume because you're using an older disassembly you know what you're doing. We want the second routine, which looks like this.

<asm> HUD_Flash: ; Routine 2 tst.w (v_rings).w ; do you have any rings? beq.s @norings ; if not, branch clr.b obFrame(a0) ; make all counters yellow jmp DisplaySprite

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@norings: moveq #0,d0 btst #3,(v_framebyte).w bne.s @display addq.w #1,d0 ; make ring counter flash red cmpi.b #9,(v_timemin).w ; have 9 minutes elapsed? bne.s @display ; if not, branch addq.w #2,d0 ; make time counter flash red

@display: move.b d0,obFrame(a0) jmp DisplaySprite </asm>

When execution flows through this routine, the first thing that happens is it checks whether you have any rings. Only if you have none is the remainder of the code (which flashes the RINGS and, if appropriate, TIME counters) executed. To fix the bug, we need to revise the routine so it first checks if you have rings, and skips flashing the RINGS counter if you do to check the game time and, if appropriate, flash the TIME counter. The result should resemble this:

<asm> HUD_Flash: moveq #0,d0 btst #3,(v_framebyte).w bne.s @display tst.w (v_rings).w ; do you have any rings? bne.s @rings ; if so, branch addq.w #1,d0 ; make ring counter flash red

@rings: cmpi.b #9,(v_timemin).w ; have 9 minutes elapsed? bne.s @display ; if not, branch addq.w #2,d0 ; make time counter flash red

@display: move.b d0,obFrame(a0) jmp DisplaySprite </asm>