avcodec/dds: add support for 4bpp format

Signed-off-by: Paul B Mahol <onemda@gmail.com>

libavcodec/dds.c

@@ -102,6 +102,7 @@ typedef struct DDSContext {
 
     int compressed;
     int paletted;
+    int bpp;
     enum DDSPostProc postproc;
 
     const uint8_t *tex_data; // Compressed texture
@@ -148,7 +149,7 @@ static int parse_pixel_format(AVCodecContext *avctx)
         ctx->paletted = 0;
     }
 
-    bpp = bytestream2_get_le32(gbc); // rgbbitcount
+    bpp = ctx->bpp = bytestream2_get_le32(gbc); // rgbbitcount
     r   = bytestream2_get_le32(gbc); // rbitmask
     g   = bytestream2_get_le32(gbc); // gbitmask
     b   = bytestream2_get_le32(gbc); // bbitmask
@@ -354,8 +355,11 @@ static int parse_pixel_format(AVCodecContext *avctx)
             return AVERROR_INVALIDDATA;
         }
     } else {
+        /*  4 bpp */
+        if (bpp == 4 && r == 0 && g == 0 && b == 0 && a == 0)
+            avctx->pix_fmt = AV_PIX_FMT_PAL8;
         /*  8 bpp */
-        if (bpp == 8 && r == 0xff && g == 0 && b == 0 && a == 0)
+        else if (bpp == 8 && r == 0xff && g == 0 && b == 0 && a == 0)
             avctx->pix_fmt = AV_PIX_FMT_GRAY8;
         else if (bpp == 8 && r == 0 && g == 0 && b == 0 && a == 0xff)
             avctx->pix_fmt = AV_PIX_FMT_GRAY8;
@@ -676,6 +680,36 @@ static int dds_decode(AVCodecContext *avctx, void *data,
         /* Use the decompress function on the texture, one block per thread. */
         ctx->tex_data = gbc->buffer;
         avctx->execute2(avctx, decompress_texture_thread, frame, NULL, ctx->slice_count);
+    } else if (!ctx->paletted && ctx->bpp == 4) {
+        uint8_t *dst = frame->data[0];
+        int x, y, i;
+
+        /* Use the first 64 bytes as palette, then copy the rest. */
+        bytestream2_get_buffer(gbc, frame->data[1], 16 * 4);
+        for (i = 0; i < 16; i++) {
+            AV_WN32(frame->data[1] + i*4,
+                    (frame->data[1][2+i*4]<<0)+
+                    (frame->data[1][1+i*4]<<8)+
+                    (frame->data[1][0+i*4]<<16)+
+                    (frame->data[1][3+i*4]<<24)
+            );
+        }
+        frame->palette_has_changed = 1;
+
+        if (bytestream2_get_bytes_left(gbc) < frame->height * frame->width / 2) {
+            av_log(avctx, AV_LOG_ERROR, "Buffer is too small (%d < %d).\n",
+                   bytestream2_get_bytes_left(gbc), frame->height * frame->width / 2);
+            return AVERROR_INVALIDDATA;
+        }
+
+        for (y = 0; y < frame->height; y++) {
+            for (x = 0; x < frame->width; x += 2) {
+                uint8_t val = bytestream2_get_byte(gbc);
+                dst[x    ] = val & 0xF;
+                dst[x + 1] = val >> 4;
+            }
+            dst += frame->linesize[0];
+        }
     } else {
         int linesize = av_image_get_linesize(avctx->pix_fmt, frame->width, 0);