[FFmpeg-devel] [PATCH 2/2] avcodec/dds: fix for missing pixels at the bottom of frames

[Tom Butterworth]

A bug was introduced in 6b2b26e7af3ede0abfb46eb5725c26d1083f50bc whereby when
frame height wasn't divisible by the number of threads, pixels would be omitted
from the bottom rows during decode.
---
 libavcodec/dds.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/libavcodec/dds.c b/libavcodec/dds.c
index a01ed7d..7e1d60a 100644
--- a/libavcodec/dds.c
+++ b/libavcodec/dds.c
@@ -106,6 +106,7 @@ typedef struct DDSContext {
     const uint8_t *tex_data; // Compressed texture
     int tex_ratio;           // Compression ratio
     int slice_size;          // Optimal slice size
+    int slice_count;         // Number of slices for threaded operations
 
     /* Pointer to the selected compress or decompress function. */
     int (*tex_funct)(uint8_t *dst, ptrdiff_t stride, const uint8_t *block);
@@ -425,7 +426,12 @@ static int decompress_texture_thread(AVCodecContext *avctx, void *arg,
     int start_slice, end_slice;
 
     start_slice = slice * ctx->slice_size;
-    end_slice   = FFMIN(start_slice + ctx->slice_size, avctx->coded_height);
+    /* If the frame height isn't divisible by the number of slices then the
+     * last slice must cover more rows than ctx->slice_size */
+    if (slice == ctx->slice_count - 1)
+        end_slice = avctx->coded_height;
+    else
+        end_slice = FFMIN(start_slice + ctx->slice_size, avctx->coded_height);
 
     start_slice /= TEXTURE_BLOCK_H;
     end_slice   /= TEXTURE_BLOCK_H;
@@ -633,13 +639,13 @@ static int dds_decode(AVCodecContext *avctx, void *data,
         return ret;
 
     if (ctx->compressed) {
-        int slices = FFMIN(avctx->thread_count,
-                           avctx->coded_height / TEXTURE_BLOCK_H);
-        ctx->slice_size = avctx->coded_height / slices;
+        ctx->slice_count = av_clip(avctx->thread_count, 1,
+                                   avctx->coded_height / TEXTURE_BLOCK_H);
+        ctx->slice_size = avctx->coded_height / ctx->slice_count;
 
         /* Use the decompress function on the texture, one block per thread. */
         ctx->tex_data = gbc->buffer;
-        avctx->execute2(avctx, decompress_texture_thread, frame, NULL, slices);
+        avctx->execute2(avctx, decompress_texture_thread, frame, NULL, ctx->slice_count);
     } else {
         int linesize = av_image_get_linesize(avctx->pix_fmt, frame->width, 0);
 
-- 
2.3.2 (Apple Git-55)