From 89bc80f1ae5bd99db448eccbc19ba2981722da1f Mon Sep 17 00:00:00 2001 From: Sam Lantinga Date: Fri, 16 Aug 2013 06:59:19 -0700 Subject: [PATCH] Fixed alpha blending for the MMX blit functions I see the Remarks of function SDL_BlitSurface shows that "when SDL_BLENDMODE_BLEND, we have dstA = srcA + (dstA * (1-srcA))". however, I tested some pictures but the result implies "dstA=arcA" actually. I stepped into the source code, and found after I set SDL_BLENDMODE_BLEND for the source surface, the final blit function is BlitRGBtoRGBPixelAlphaMMX when I use SDL_BlitSurface on my computer. And I found these codes: else if (alpha == amask) { /* opaque alpha -- copy RGB, keep dst alpha */ *dstp = (*srcp & chanmask) | (*dstp & ~chanmask); The same code is used in BlitRGBtoRGBPixelAlphaMMX3DNOW and BlitRGBtoRGBPixelAlpha. So I think they still keep dst alpha. Best regards, Jianyu Guan --- src/video/SDL_blit_A.c | 74 ++++++++++++++++++++++-------------------- 1 file changed, 38 insertions(+), 36 deletions(-) diff --git a/src/video/SDL_blit_A.c b/src/video/SDL_blit_A.c index 3fb89c0612dbd..e53f99a8337a8 100644 --- a/src/video/SDL_blit_A.c +++ b/src/video/SDL_blit_A.c @@ -337,15 +337,14 @@ BlitRGBtoRGBPixelAlphaMMX(SDL_BlitInfo * info) Uint32 chanmask = sf->Rmask | sf->Gmask | sf->Bmask; Uint32 amask = sf->Amask; Uint32 ashift = sf->Ashift; - Uint64 multmask; + Uint64 multmask, multmask2; - __m64 src1, dst1, mm_alpha, mm_zero, dmask; + __m64 src1, dst1, mm_alpha, mm_zero, mm_alpha2; mm_zero = _mm_setzero_si64(); /* 0 -> mm_zero */ - multmask = 0xFFFF; - multmask <<= (ashift * 2); - multmask = ~multmask; - dmask = *(__m64 *) & multmask; /* dst alpha mask -> dmask */ + multmask = 0x00FF; + multmask <<= (ashift * 2); + multmask2 = 0x00FF00FF00FF00FF; while (height--) { /* *INDENT-OFF* */ @@ -353,9 +352,8 @@ BlitRGBtoRGBPixelAlphaMMX(SDL_BlitInfo * info) Uint32 alpha = *srcp & amask; if (alpha == 0) { /* do nothing */ - } else if (alpha == amask) { - /* opaque alpha -- copy RGB, keep dst alpha */ - *dstp = (*srcp & chanmask) | (*dstp & ~chanmask); + } else if (alpha == amask || (*dstp & amask) == 0) { + *dstp = *srcp; } else { src1 = _mm_cvtsi32_si64(*srcp); /* src(ARGB) -> src1 (0000ARGB)*/ src1 = _mm_unpacklo_pi8(src1, mm_zero); /* 0A0R0G0B -> src1 */ @@ -366,15 +364,17 @@ BlitRGBtoRGBPixelAlphaMMX(SDL_BlitInfo * info) mm_alpha = _mm_cvtsi32_si64(alpha); /* alpha -> mm_alpha (0000000A) */ mm_alpha = _mm_srli_si64(mm_alpha, ashift); /* mm_alpha >> ashift -> mm_alpha(0000000A) */ mm_alpha = _mm_unpacklo_pi16(mm_alpha, mm_alpha); /* 00000A0A -> mm_alpha */ - mm_alpha = _mm_unpacklo_pi32(mm_alpha, mm_alpha); /* 0A0A0A0A -> mm_alpha */ - mm_alpha = _mm_and_si64(mm_alpha, dmask); /* 000A0A0A -> mm_alpha, preserve dst alpha on add */ + mm_alpha2 = _mm_unpacklo_pi32(mm_alpha, mm_alpha); /* 0A0A0A0A -> mm_alpha2 */ + mm_alpha = _mm_or_si64(mm_alpha2, *(__m64 *) & multmask); /* 0F0A0A0A -> mm_alpha*/ + mm_alpha2 = _mm_xor_si64(mm_alpha2, *(__m64 *) & multmask2); /* 255 - mm_alpha -> mm_alpha*/ /* blend */ - src1 = _mm_sub_pi16(src1, dst1);/* src1 - dst1 -> src1 */ - src1 = _mm_mullo_pi16(src1, mm_alpha); /* (src1 - dst1) * alpha -> src1 */ - src1 = _mm_srli_pi16(src1, 8); /* src1 >> 8 -> src1(000R0G0B) */ - dst1 = _mm_add_pi8(src1, dst1); /* src1 + dst1 -> dst1(0A0R0G0B) */ - dst1 = _mm_packs_pu16(dst1, mm_zero); /* 0000ARGB -> dst1 */ + src1 = _mm_mullo_pi16(src1, mm_alpha); + src1 = _mm_srli_pi16(src1, 8); + dst1 = _mm_mullo_pi16(dst1, mm_alpha2); + dst1 = _mm_srli_pi16(dst1, 8); + dst1 = _mm_add_pi16(src1, dst1); + dst1 = _mm_packs_pu16(dst1, mm_zero); *dstp = _mm_cvtsi64_si32(dst1); /* dst1 -> pixel */ } @@ -481,23 +481,24 @@ BlitRGBtoRGBPixelAlpha(SDL_BlitInfo * info) compositioning used (>>8 instead of /255) doesn't handle it correctly. Also special-case alpha=0 for speed? Benchmark this! */ - if(alpha) { - if(alpha == SDL_ALPHA_OPAQUE) { - *dstp = (s & 0x00ffffff) | (*dstp & 0xff000000); + if (alpha) { + if (alpha == SDL_ALPHA_OPAQUE) { + *dstp = *srcp; } else { /* * take out the middle component (green), and process * the other two in parallel. One multiply less. */ d = *dstp; - dalpha = d & 0xff000000; + dalpha = d >> 24; s1 = s & 0xff00ff; d1 = d & 0xff00ff; d1 = (d1 + ((s1 - d1) * alpha >> 8)) & 0xff00ff; s &= 0xff00; d &= 0xff00; d = (d + ((s - d) * alpha >> 8)) & 0xff00; - *dstp = d1 | d | dalpha; + dalpha = alpha + (dalpha * (alpha ^ 0xFF) >> 8); + *dstp = d1 | d | (dalpha << 24); } } ++srcp; @@ -524,15 +525,14 @@ BlitRGBtoRGBPixelAlphaMMX3DNOW(SDL_BlitInfo * info) Uint32 chanmask = sf->Rmask | sf->Gmask | sf->Bmask; Uint32 amask = sf->Amask; Uint32 ashift = sf->Ashift; - Uint64 multmask; + Uint64 multmask, multmask2; - __m64 src1, dst1, mm_alpha, mm_zero, dmask; + __m64 src1, dst1, mm_alpha, mm_zero, mm_alpha2; mm_zero = _mm_setzero_si64(); /* 0 -> mm_zero */ - multmask = 0xFFFF; + multmask = 0x00FF; multmask <<= (ashift * 2); - multmask = ~multmask; - dmask = *(__m64 *) & multmask; /* dst alpha mask -> dmask */ + multmask2 = 0x00FF00FF00FF00FF; while (height--) { /* *INDENT-OFF* */ @@ -545,9 +545,8 @@ BlitRGBtoRGBPixelAlphaMMX3DNOW(SDL_BlitInfo * info) alpha = *srcp & amask; if (alpha == 0) { /* do nothing */ - } else if (alpha == amask) { - /* copy RGB, keep dst alpha */ - *dstp = (*srcp & chanmask) | (*dstp & ~chanmask); + } else if (alpha == amask || (*dstp & amask) == 0) { + *dstp = *srcp; } else { src1 = _mm_cvtsi32_si64(*srcp); /* src(ARGB) -> src1 (0000ARGB)*/ src1 = _mm_unpacklo_pi8(src1, mm_zero); /* 0A0R0G0B -> src1 */ @@ -558,15 +557,18 @@ BlitRGBtoRGBPixelAlphaMMX3DNOW(SDL_BlitInfo * info) mm_alpha = _mm_cvtsi32_si64(alpha); /* alpha -> mm_alpha (0000000A) */ mm_alpha = _mm_srli_si64(mm_alpha, ashift); /* mm_alpha >> ashift -> mm_alpha(0000000A) */ mm_alpha = _mm_unpacklo_pi16(mm_alpha, mm_alpha); /* 00000A0A -> mm_alpha */ - mm_alpha = _mm_unpacklo_pi32(mm_alpha, mm_alpha); /* 0A0A0A0A -> mm_alpha */ - mm_alpha = _mm_and_si64(mm_alpha, dmask); /* 000A0A0A -> mm_alpha, preserve dst alpha on add */ + mm_alpha2 = _mm_unpacklo_pi32(mm_alpha, mm_alpha); /* 0A0A0A0A -> mm_alpha2 */ + mm_alpha = _mm_or_si64(mm_alpha2, *(__m64 *) & multmask); /* 0F0A0A0A -> mm_alpha*/ + mm_alpha2 = _mm_xor_si64(mm_alpha2, *(__m64 *) & multmask2); /* 255 - mm_alpha -> mm_alpha*/ + /* blend */ - src1 = _mm_sub_pi16(src1, dst1);/* src - dst -> src1 */ - src1 = _mm_mullo_pi16(src1, mm_alpha); /* (src - dst) * alpha -> src1 */ - src1 = _mm_srli_pi16(src1, 8); /* src1 >> 8 -> src1(000R0G0B) */ - dst1 = _mm_add_pi8(src1, dst1); /* src1 + dst1(dst) -> dst1(0A0R0G0B) */ - dst1 = _mm_packs_pu16(dst1, mm_zero); /* 0000ARGB -> dst1 */ + src1 = _mm_mullo_pi16(src1, mm_alpha); + src1 = _mm_srli_pi16(src1, 8); + dst1 = _mm_mullo_pi16(dst1, mm_alpha2); + dst1 = _mm_srli_pi16(dst1, 8); + dst1 = _mm_add_pi16(src1, dst1); + dst1 = _mm_packs_pu16(dst1, mm_zero); *dstp = _mm_cvtsi64_si32(dst1); /* dst1 -> pixel */ }