--- /dev/null
+; vi:ft=nasm:
+ section .text
+ bits 32
+
+ global fade_image
+fade_image:
+ push ebp
+ mov ebp, esp
+ push ebx
+
+ mov eax, [ebp + 8]
+ mov edx, [ebp + 12]
+ mov ebx, [ebp + 16]
+ call fade_image_
+
+ pop ebx
+ pop ebp
+ ret
+
+ ; void fade_image(uint16_t *dest, uint32_t *src, uint16_t fade)
+ ; - dest points to a 16bit 565 framebuffer
+ ; - src points to a 32bit RGBX image
+ ; - fade is 24.8 fixed point [0, 1]
+ ; watcom register calling convention arguments: eax, edx, ebx
+ global fade_image_
+fade_image_:
+ push ecx
+ push edi
+
+ mov ecx, 640 * 480
+ mov edi, eax
+
+ ; take fade and duplicate it across all words of mm1
+ movd mm1, ebx ; mm1 [00|00|00|VV]
+ punpckldq mm1, mm1 ; mm1 [00|VV|00|VV]
+ packssdw mm1, mm1 ; mm1 [VV|VV|VV|VV]
+.loop:
+ ; grab RGB32 pixel and unpack it to zero-extended words in mm0
+ movd mm0, [edx] ; mm0 [??|??|?R|GB]
+ add edx, 4
+ pxor mm7, mm7
+ punpcklbw mm0, mm7 ; mm0 [0?|0R|0G|0B]
+ ; multiply by fade and divide by 256 to drop the decimal part
+ pmullw mm0, mm1
+ psrlw mm0, 10 ; 8 for the div + 2 to make them 666, easier 565 packing
+ ; pack result into 565 in ax
+ packuswb mm0, mm0
+ movd eax, mm0
+ mov ebx, eax
+ shr al, 1 ; blue in position [........|00RRRRRR|00GGGGGG|000BBBBB]
+ xor bl, bl
+ shr bx, 3
+ xor ah, ah
+ or ax, bx ; green in position ...|00RRRRRR|00000GGG|GGGBBBBB]
+ shr ebx, 6
+ and ebx, 0f800h
+ or eax, ebx ; done [RRRRRGGG|GGGBBBBB]
+ mov [edi], ax
+ add edi, 2
+
+ dec ecx
+ jnz .loop
+
+ emms ; clear fpu state
+
+ pop edi
+ pop ecx
+ ret
projects / eradicate / blobdiff