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Fade out assembly code keeps looping. Can not figure out why it keeps looping.

yaboiryan · 2021-07-29T09:32:09

I tried writing a fade out function for my MS-DOS game in assembly. The function works, but however, it keeps looping endlessly for some reason, and I can not figure out why it wont stop doing so. Here is what I have: AFObeg equ [bp+4] AFOcnt equ [bp+4+2] proc FadeOut_ near push ebx push ecx push edx mov ebp,esp push ds push esi push edi push ds ; get data segment into es pop es mov edx, offset _WorkPalette push edx ; save offset of opal xor ebx, ebx mov ecx, 100h mov eax, 1017h ; bios read dac registers function int 10h ; read the palette registers into opal pop edi ; offset of opal, was in dx! mov eax, AFObeg ; get offset of first palette byte to mov ebx, 3 ; be processed mul ebx add edi, eax ; adjust offset into opal mov eax, AFOcnt ; find the number of bytes to be processed mov ebx, 3 mul ebx ; leave it in ax mov ecx, 64 ; 64 passes through fade loop o_fade_loop: push ecx ; save the fade loop counter push edi ; save offset of first byte processed in mov bl, cl ; we'll use the pass number as a threshold mov ecx, eax ; load number of bytes to process into cx o_pal_cmp_loop: cmp bl, es:[edi] ; start decrementing when palette value jnz o_no_dec ; is equal loop count (it will stay equal dec BYTE PTR es:[edi] ; to loop count for the rest of this pass) o_no_dec: inc edi loop o_pal_cmp_loop ; do the next byte mov ebx, esp ; need the stack pointer for a moment mov di, ss:[ebx] ; restore offset into pal without popping mov ecx, AFOcnt ; number of triplets to process push eax ; need to use ax for port i/o mov edx, 03DAh ; CRT controller input status 1 register o_vbi_1: in al, dx ; watch vertical blanking bit test al,08h ; wait for it to clear to make sure jnz o_vbi_1 ; we're not in a blanking interval o_vbi_2: in al, dx ; now wait for the start of the test al,08h ; next blanking interval jz o_vbi_2 mov ah, AFObeg ; get first register to process into ah mov dx, 03c8h ; DAC palette index register o_pal_load_loop: mov al, ah ; get next palette number to write out dx, al ; write the register number to the dac inc dx ; address dac data register mov al, BYTE PTR es:[di] ; get first byte of triplet out dx, al ; write it to the dac data register inc edi ; point to second byte mov al, BYTE PTR es:[di] ; get second byte of triplet out dx, al ; write it to the dac data register inc edi ; point to third byte mov al, BYTE PTR es:[di] ; get third byte of triplet out dx, al ; write it to the dac data register inc edi ; point to first byte of next triplet dec edx ; address the da21c index register inc ah ; point to next palette register loop o_pal_load_loop ; process next triplet pop eax ; restore ax pop edi ; restore the offset into pal pop ecx ; restore the fade loop counter loop o_fade_loop ; do the next pass through the fade loop pop edi pop esi pop ds pop ebp ret endp ;end of the fade out function This is the result of the effect tested out on my (very poorly made) level select screen. The effect works to an extent, but when it fades out, it does not stop the fade out, but it restarts the fading out process, and it keeps on looping forever. Please let me know what yall's thoughts are about how I could fix the issue. Any help is greatly appreciated. I had asked this in a previous question, but it kinda died out… I also asked the question on another website.

Graphics and GPU Programming Programming Graphics game assembly dos

Started by yaboiryan June 22, 2021 03:23 AM

9 comments, last by Winternight 2 years, 10 months ago

Winternight

July 29, 2021 09:32 AM

To be completely honest…. Your youtube vid looks a hell of alot like what I remember from old Commodore 64 loading screens. Not from what I remember of MS-DOSENT.

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Fade out assembly code keeps looping. Can not figure out why it keeps looping.

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🎉 Celebrating 25 Years of GameDev.net! 🎉

Fade out assembly code keeps looping. Can not figure out why it keeps looping.

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