avcodec/pngdec: support alpha blending for palette apng

Update clock test, as PAL8 apngs are now decoded as RGBA.

2 files changed, 72 insertions, 69 deletions

diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
index 39bb652f67..a335a29b08 100644
--- a/libavcodec/pngdec.c
+++ b/libavcodec/pngdec.c
@@ -677,7 +677,7 @@ static int decode_idat_chunk(AVCodecContext *avctx, PNGDecContext *s,
             avctx->pix_fmt = AV_PIX_FMT_RGBA64BE;
         } else if ((s->bits_per_pixel == 1 || s->bits_per_pixel == 2 || s->bits_per_pixel == 4 || s->bits_per_pixel == 8) &&
                 s->color_type == PNG_COLOR_TYPE_PALETTE) {
-            avctx->pix_fmt = AV_PIX_FMT_PAL8;
+            avctx->pix_fmt = avctx->codec_id == AV_CODEC_ID_APNG ? AV_PIX_FMT_RGBA : AV_PIX_FMT_PAL8;
         } else if (s->bit_depth == 1 && s->bits_per_pixel == 1 && avctx->codec_id != AV_CODEC_ID_APNG) {
             avctx->pix_fmt = AV_PIX_FMT_MONOBLACK;
         } else if (s->bit_depth == 8 &&
@@ -1022,7 +1022,6 @@ static int decode_fctl_chunk(AVCodecContext *avctx, PNGDecContext *s,
     if (blend_op == APNG_BLEND_OP_OVER && !s->has_trns && (
             avctx->pix_fmt == AV_PIX_FMT_RGB24 ||
             avctx->pix_fmt == AV_PIX_FMT_RGB48BE ||
-            avctx->pix_fmt == AV_PIX_FMT_PAL8 ||
             avctx->pix_fmt == AV_PIX_FMT_GRAY8 ||
             avctx->pix_fmt == AV_PIX_FMT_GRAY16BE ||
             avctx->pix_fmt == AV_PIX_FMT_MONOBLACK
@@ -1070,13 +1069,13 @@ static int handle_p_frame_apng(AVCodecContext *avctx, PNGDecContext *s,
     ptrdiff_t      dst_stride = p->linesize[0];
     const uint8_t *src        = s->last_picture.f->data[0];
     ptrdiff_t      src_stride = s->last_picture.f->linesize[0];
+    const int      bpp        = s->color_type == PNG_COLOR_TYPE_PALETTE ? 4 : s->bpp;
 
     size_t x, y;
 
     if (s->blend_op == APNG_BLEND_OP_OVER &&
         avctx->pix_fmt != AV_PIX_FMT_RGBA &&
-        avctx->pix_fmt != AV_PIX_FMT_GRAY8A &&
-        avctx->pix_fmt != AV_PIX_FMT_PAL8) {
+        avctx->pix_fmt != AV_PIX_FMT_GRAY8A) {
         avpriv_request_sample(avctx, "Blending with pixel format %s",
                               av_get_pix_fmt_name(avctx->pix_fmt));
         return AVERROR_PATCHWELCOME;
@@ -1095,7 +1094,7 @@ static int handle_p_frame_apng(AVCodecContext *avctx, PNGDecContext *s,
 
         for (y = s->last_y_offset; y < s->last_y_offset + s->last_h; y++) {
             memset(s->background_buf + src_stride * y +
-                   s->bpp * s->last_x_offset, 0, s->bpp * s->last_w);
+                   bpp * s->last_x_offset, 0, bpp * s->last_w);
         }
 
         src = s->background_buf;
@@ -1103,22 +1102,22 @@ static int handle_p_frame_apng(AVCodecContext *avctx, PNGDecContext *s,
 
     // copy unchanged rectangles from the last frame
     for (y = 0; y < s->y_offset; y++)
-        memcpy(dst + y * dst_stride, src + y * src_stride, p->width * s->bpp);
+        memcpy(dst + y * dst_stride, src + y * src_stride, p->width * bpp);
     for (y = s->y_offset; y < s->y_offset + s->cur_h; y++) {
-        memcpy(dst + y * dst_stride, src + y * src_stride, s->x_offset * s->bpp);
-        memcpy(dst + y * dst_stride + (s->x_offset + s->cur_w) * s->bpp,
-               src + y * src_stride + (s->x_offset + s->cur_w) * s->bpp,
-               (p->width - s->cur_w - s->x_offset) * s->bpp);
+        memcpy(dst + y * dst_stride, src + y * src_stride, s->x_offset * bpp);
+        memcpy(dst + y * dst_stride + (s->x_offset + s->cur_w) * bpp,
+               src + y * src_stride + (s->x_offset + s->cur_w) * bpp,
+               (p->width - s->cur_w - s->x_offset) * bpp);
     }
     for (y = s->y_offset + s->cur_h; y < p->height; y++)
-        memcpy(dst + y * dst_stride, src + y * src_stride, p->width * s->bpp);
+        memcpy(dst + y * dst_stride, src + y * src_stride, p->width * bpp);
 
     if (s->blend_op == APNG_BLEND_OP_OVER) {
         // Perform blending
         for (y = s->y_offset; y < s->y_offset + s->cur_h; ++y) {
-            uint8_t       *foreground = dst + dst_stride * y + s->bpp * s->x_offset;
-            const uint8_t *background = src + src_stride * y + s->bpp * s->x_offset;
-            for (x = s->x_offset; x < s->x_offset + s->cur_w; ++x, foreground += s->bpp, background += s->bpp) {
+            uint8_t       *foreground = dst + dst_stride * y + bpp * s->x_offset;
+            const uint8_t *background = src + src_stride * y + bpp * s->x_offset;
+            for (x = s->x_offset; x < s->x_offset + s->cur_w; ++x, foreground += bpp, background += bpp) {
                 size_t b;
                 uint8_t foreground_alpha, background_alpha, output_alpha;
                 uint8_t output[10];
@@ -1137,32 +1136,21 @@ static int handle_p_frame_apng(AVCodecContext *avctx, PNGDecContext *s,
                     foreground_alpha = foreground[1];
                     background_alpha = background[1];
                     break;
-
-                case AV_PIX_FMT_PAL8:
-                    foreground_alpha = s->palette[foreground[0]] >> 24;
-                    background_alpha = s->palette[background[0]] >> 24;
-                    break;
                 }
 
                 if (foreground_alpha == 255)
                     continue;
 
                 if (foreground_alpha == 0) {
-                    memcpy(foreground, background, s->bpp);
-                    continue;
-                }
-
-                if (avctx->pix_fmt == AV_PIX_FMT_PAL8) {
-                    // TODO: Alpha blending with PAL8 will likely need the entire image converted over to RGBA first
-                    avpriv_request_sample(avctx, "Alpha blending palette samples");
+                    memcpy(foreground, background, bpp);
                     continue;
                 }
 
                 output_alpha = foreground_alpha + FAST_DIV255((255 - foreground_alpha) * background_alpha);
 
-                av_assert0(s->bpp <= 10);
+                av_assert0(bpp <= 10);
 
-                for (b = 0; b < s->bpp - 1; ++b) {
+                for (b = 0; b < bpp - 1; ++b) {
                     if (output_alpha == 0) {
                         output[b] = 0;
                     } else if (background_alpha == 255) {
@@ -1172,7 +1160,7 @@ static int handle_p_frame_apng(AVCodecContext *avctx, PNGDecContext *s,
                     }
                 }
                 output[b] = output_alpha;
-                memcpy(foreground, output, s->bpp);
+                memcpy(foreground, output, bpp);
             }
         }
     }
@@ -1368,6 +1356,21 @@ exit_loop:
     if (s->bits_per_pixel <= 4)
         handle_small_bpp(s, p);
 
+    if (s->color_type == PNG_COLOR_TYPE_PALETTE && avctx->codec_id == AV_CODEC_ID_APNG) {
+        for (int y = 0; y < s->height; y++) {
+            uint8_t *row = &p->data[0][p->linesize[0] * y];
+
+            for (int x = s->width - 1; x >= 0; x--) {
+                const uint8_t idx = row[x];
+
+                row[4*x+2] =  s->palette[idx]        & 0xFF;
+                row[4*x+1] = (s->palette[idx] >> 8 ) & 0xFF;
+                row[4*x+0] = (s->palette[idx] >> 16) & 0xFF;
+                row[4*x+3] =  s->palette[idx] >> 24;
+            }
+        }
+    }
+
     /* apply transparency if needed */
     if (s->has_trns && s->color_type != PNG_COLOR_TYPE_PALETTE) {
         size_t byte_depth = s->bit_depth > 8 ? 2 : 1;
diff --git a/tests/ref/fate/apng-clock b/tests/ref/fate/apng-clock
index c0480fd4e6..26afc94c19 100644
--- a/tests/ref/fate/apng-clock
+++ b/tests/ref/fate/apng-clock
@@ -3,43 +3,43 @@
 #codec_id 0: rawvideo
 #dimensions 0: 150x150
 #sar 0: 0/1
-0,          0,          0,        1,    23524, 0xf09caaa1
-0,          1,          1,        1,    23524, 0x1a329f21
-0,          2,          2,        1,    23524, 0x9b0ca017
-0,          3,          3,        1,    23524, 0x73b09deb
-0,          4,          4,        1,    23524, 0x23039f49
-0,          5,          5,        1,    23524, 0x58869e7b
-0,          6,          6,        1,    23524, 0xc26397d2
-0,          7,          7,        1,    23524, 0xe07f7d87
-0,          8,          8,        1,    23524, 0x619a82ba
-0,          9,          9,        1,    23524, 0x696c9757
-0,         10,         10,        1,    23524, 0x7303a4a6
-0,         11,         11,        1,    23524, 0x1e149aee
-0,         12,         12,        1,    23524, 0x78dd97e0
-0,         13,         13,        1,    23524, 0xad8092d3
-0,         14,         14,        1,    23524, 0x27c090b4
-0,         15,         15,        1,    23524, 0x904c97be
-0,         16,         16,        1,    23524, 0x54d29b9e
-0,         17,         17,        1,    23524, 0x57689bfa
-0,         18,         18,        1,    23524, 0x2772a00e
-0,         19,         19,        1,    23524, 0x6a769ef6
-0,         20,         20,        1,    23524, 0x94d8aad5
-0,         21,         21,        1,    23524, 0x52f79ec4
-0,         22,         22,        1,    23524, 0x99ee9fbc
-0,         23,         23,        1,    23524, 0xbd6a9e4d
-0,         24,         24,        1,    23524, 0xaf4aa1cf
-0,         25,         25,        1,    23524, 0xdb929f98
-0,         26,         26,        1,    23524, 0x9e189a6f
-0,         27,         27,        1,    23524, 0x3ffb9410
-0,         28,         28,        1,    23524, 0x6fc9917d
-0,         29,         29,        1,    23524, 0xe43e94ca
-0,         30,         30,        1,    23524, 0x03b6a24f
-0,         31,         31,        1,    23524, 0xc54f99b3
-0,         32,         32,        1,    23524, 0x4b9a9748
-0,         33,         33,        1,    23524, 0x25a19003
-0,         34,         34,        1,    23524, 0x2b9d77cc
-0,         35,         35,        1,    23524, 0x4a5a9217
-0,         36,         36,        1,    23524, 0x241b9a7c
-0,         37,         37,        1,    23524, 0xc9d39b38
-0,         38,         38,        1,    23524, 0xcca69f30
-0,         39,         39,        1,    23524, 0xe50f9ec9
+0,          0,          0,        1,    90000, 0x11af5588
+0,          1,          1,        1,    90000, 0x528c2eb8
+0,          2,          2,        1,    90000, 0xebae2d82
+0,          3,          3,        1,    90000, 0xf57951ef
+0,          4,          4,        1,    90000, 0xc2a84734
+0,          5,          5,        1,    90000, 0x2dd74265
+0,          6,          6,        1,    90000, 0x5a6980cb
+0,          7,          7,        1,    90000, 0x519373e4
+0,          8,          8,        1,    90000, 0xdca835fb
+0,          9,          9,        1,    90000, 0xc8a46d5e
+0,         10,         10,        1,    90000, 0xa01a72e3
+0,         11,         11,        1,    90000, 0xacd751fa
+0,         12,         12,        1,    90000, 0x464b6d39
+0,         13,         13,        1,    90000, 0x56f1b22c
+0,         14,         14,        1,    90000, 0x0595a6bb
+0,         15,         15,        1,    90000, 0xb9418cdc
+0,         16,         16,        1,    90000, 0x8b2b7bcf
+0,         17,         17,        1,    90000, 0x1a026aaf
+0,         18,         18,        1,    90000, 0x25443715
+0,         19,         19,        1,    90000, 0x3d9231cd
+0,         20,         20,        1,    90000, 0xfef153a8
+0,         21,         21,        1,    90000, 0x6a7c2e7b
+0,         22,         22,        1,    90000, 0x1fe92cda
+0,         23,         23,        1,    90000, 0x30554ff8
+0,         24,         24,        1,    90000, 0x57e544d9
+0,         25,         25,        1,    90000, 0x4c2d3b69
+0,         26,         26,        1,    90000, 0x22c26e0c
+0,         27,         27,        1,    90000, 0x254bb498
+0,         28,         28,        1,    90000, 0xcd02a4ac
+0,         29,         29,        1,    90000, 0x54447feb
+0,         30,         30,        1,    90000, 0x9dc87b6e
+0,         31,         31,        1,    90000, 0xfb49553b
+0,         32,         32,        1,    90000, 0x05316fbe
+0,         33,         33,        1,    90000, 0xd796da15
+0,         34,         34,        1,    90000, 0x36064111
+0,         35,         35,        1,    90000, 0x470cb58e
+0,         36,         36,        1,    90000, 0xf0ba8054
+0,         37,         37,        1,    90000, 0x3f496ff8
+0,         38,         38,        1,    90000, 0xe3a43cff
+0,         39,         39,        1,    90000, 0xacdd36ce