From 235c87dc92c9bc9a1b5c30a3a52b8ca17653b7dd Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Wed, 25 Sep 2024 21:54:05 -0700
Subject: [PATCH] Don't use BlitARGBto555PixelAlpha() for
SDL_PIXELFORMAT_ARGB1555
This didn't properly take into account destination alpha.
Fixes https://github.com/libsdl-org/SDL/issues/8401
(cherry picked from commit 1aea43846e0286d44d3249a02220dab222e38218)
(cherry picked from commit c9f3cbe02f1b81f6591608f0f19b35c7d3a1347c)
---
src/video/SDL_blit_A.c | 20 ++++++++------------
1 file changed, 8 insertions(+), 12 deletions(-)
diff --git a/src/video/SDL_blit_A.c b/src/video/SDL_blit_A.c
index 2cf00e0a2c06b..96fec1b478fc8 100644
--- a/src/video/SDL_blit_A.c
+++ b/src/video/SDL_blit_A.c
@@ -1222,10 +1222,9 @@ static void BlitARGBto565PixelAlpha(SDL_BlitInfo *info)
DUFFS_LOOP4({
Uint32 s = *srcp;
unsigned alpha = s >> 27; /* downscale alpha to 5 bits */
- /* FIXME: Here we special-case opaque alpha since the
+ /* Here we special-case opaque alpha since the
compositioning used (>>8 instead of /255) doesn't handle
- it correctly. Also special-case alpha=0 for speed?
- Benchmark this! */
+ it correctly. */
if (alpha) {
if (alpha == (SDL_ALPHA_OPAQUE >> 3)) {
*dstp = (Uint16)((s >> 8 & 0xf800) + (s >> 5 & 0x7e0) + (s >> 3 & 0x1f));
@@ -1235,8 +1234,7 @@ static void BlitARGBto565PixelAlpha(SDL_BlitInfo *info)
* convert source and destination to G0RAB65565
* and blend all components at the same time
*/
- s = ((s & 0xfc00) << 11) + (s >> 8 & 0xf800)
- + (s >> 3 & 0x1f);
+ s = ((s & 0xfc00) << 11) + (s >> 8 & 0xf800) + (s >> 3 & 0x1f);
d = (d | d << 16) & 0x07e0f81f;
d += (s - d) * alpha >> 5;
d &= 0x07e0f81f;
@@ -1268,21 +1266,19 @@ static void BlitARGBto555PixelAlpha(SDL_BlitInfo *info)
unsigned alpha;
Uint32 s = *srcp;
alpha = s >> 27; /* downscale alpha to 5 bits */
- /* FIXME: Here we special-case opaque alpha since the
+ /* Here we special-case opaque alpha since the
compositioning used (>>8 instead of /255) doesn't handle
- it correctly. Also special-case alpha=0 for speed?
- Benchmark this! */
+ it correctly. */
if (alpha) {
if (alpha == (SDL_ALPHA_OPAQUE >> 3)) {
*dstp = (Uint16)((s >> 9 & 0x7c00) + (s >> 6 & 0x3e0) + (s >> 3 & 0x1f));
} else {
Uint32 d = *dstp;
/*
- * convert source and destination to G0RAB65565
+ * convert source and destination to G0RAB55555
* and blend all components at the same time
*/
- s = ((s & 0xf800) << 10) + (s >> 9 & 0x7c00)
- + (s >> 3 & 0x1f);
+ s = ((s & 0xf800) << 10) + (s >> 9 & 0x7c00) + (s >> 3 & 0x1f);
d = (d | d << 16) & 0x03e07c1f;
d += (s - d) * alpha >> 5;
d &= 0x03e07c1f;
@@ -1452,7 +1448,7 @@ SDL_BlitFunc SDL_CalculateBlitA(SDL_Surface *surface)
if (sf->BytesPerPixel == 4 && sf->Amask == 0xff000000 && sf->Gmask == 0xff00 && ((sf->Rmask == 0xff && df->Rmask == 0x1f) || (sf->Bmask == 0xff && df->Bmask == 0x1f))) {
if (df->Gmask == 0x7e0) {
return BlitARGBto565PixelAlpha;
- } else if (df->Gmask == 0x3e0) {
+ } else if (df->Gmask == 0x3e0 && !df->Amask) {
return BlitARGBto555PixelAlpha;
}
}