Correctly support pal8 with alpha in libswscale, fix png pal8 with alpha.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswscale/swscale.c

@@ -1158,6 +1158,16 @@ BGR2UV(uint16_t, bgr15ToUV, 0, 0, 0, 0,   0x001F, 0x03E0,   0x7C00, RU<<10, GU<<
 BGR2UV(uint16_t, rgb16ToUV, 0, 0, 0, 0,   0xF800, 0x07E0,   0x001F, RU    , GU<<5, BU<<11, RV    , GV<<5, BV<<11, RGB2YUV_SHIFT+8)
 BGR2UV(uint16_t, rgb15ToUV, 0, 0, 0, 0,   0x7C00, 0x03E0,   0x001F, RU    , GU<<5, BU<<10, RV    , GV<<5, BV<<10, RGB2YUV_SHIFT+7)
 
+static inline void palToA(uint8_t *dst, const uint8_t *src, long width, uint32_t *pal)
+{
+    int i;
+    for (i=0; i<width; i++) {
+        int d= src[i];
+
+        dst[i]= pal[d] >> 24;
+    }
+}
+
 static inline void palToY(uint8_t *dst, const uint8_t *src, long width, uint32_t *pal)
 {
     int i;
@@ -2002,6 +2012,7 @@ int sws_scale(SwsContext *c, const uint8_t* const src[], const int srcStride[],
             int p, r, g, b, y, u, v, a = 0xff;
             if(c->srcFormat == PIX_FMT_PAL8) {
                 p=((const uint32_t*)(src[1]))[i];
+                a= (p>>24)&0xFF;
                 r= (p>>16)&0xFF;
                 g= (p>> 8)&0xFF;
                 b=  p     &0xFF;

libswscale/swscale_internal.h

@@ -459,6 +459,7 @@ const char *sws_format_name(enum PixelFormat format);
         || (x)==PIX_FMT_BGR32_1     \
         || (x)==PIX_FMT_RGB32       \
         || (x)==PIX_FMT_RGB32_1     \
+        || (x)==PIX_FMT_PAL8        \
         || (x)==PIX_FMT_GRAY8A      \
         || (x)==PIX_FMT_YUVA420P    \
     )

libswscale/swscale_template.c

@@ -3068,6 +3068,7 @@ static void RENAME(sws_init_swScale)(SwsContext *c)
         case PIX_FMT_BGR32  :
         case PIX_FMT_BGR32_1: c->alpToYV12 = abgrToA; break;
         case PIX_FMT_GRAY8A : c->alpToYV12 = RENAME(yuy2ToY); break;
+        case PIX_FMT_PAL8   : c->alpToYV12 = palToA; break;
         }
     }