libavcodec/sanm: fix XPAL handling

Outlaws' RAE.SAN file did not properly fade out in certain scenes,
but simply turned to black as soon as the first XPAL chunk with
the apply command was encountered.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavcodec/sanm.c

@@ -1033,6 +1033,45 @@ static int process_frame_obj(SANMVideoContext *ctx)
     }
 }
 
+static int process_xpal(SANMVideoContext *ctx, int size)
+{
+    int16_t *dp = ctx->delta_pal;
+    uint32_t *pal = ctx->pal;
+    uint16_t cmd;
+    uint8_t c[3];
+    int i, j;
+
+    bytestream2_skip(&ctx->gb, 2);
+    cmd = bytestream2_get_be16(&ctx->gb);
+
+    if (cmd == 1) {
+        for (i = 0; i < PALETTE_DELTA; i += 3) {
+            c[0] = (*pal >> 16) & 0xFF;
+            c[1] = (*pal >>  8) & 0xFF;
+            c[2] = (*pal >>  0) & 0xFF;
+            for (j = 0; j < 3; j++) {
+                int cl = (c[j] * 129) + *dp++;
+                c[j] = av_clip_uint8(cl / 128) & 0xFF;
+            }
+            *pal++ = 0xFFU << 24 | c[0] << 16 | c[1] << 8 | c[2];
+        }
+    } else if (cmd == 2) {
+        if (size < PALETTE_DELTA * 2 + 4) {
+            av_log(ctx->avctx, AV_LOG_ERROR,
+                   "Incorrect palette change block size %"PRIu32".\n", size);
+            return AVERROR_INVALIDDATA;
+        }
+        for (i = 0; i < PALETTE_DELTA; i++)
+            dp[i] = bytestream2_get_le16u(&ctx->gb);
+
+        if (size >= PALETTE_DELTA * 2 + 4 + PALETTE_SIZE * 3) {
+            for (i = 0; i < PALETTE_SIZE; i++)
+                ctx->pal[i] = 0xFFU << 24 | bytestream2_get_be24u(&ctx->gb);
+        }
+    }
+    return 0;
+}
+
 static int decode_0(SANMVideoContext *ctx)
 {
     uint16_t *frm = ctx->frm0;
@@ -1472,34 +1511,8 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *frame,
                     return ret;
                 break;
             case MKBETAG('X', 'P', 'A', 'L'):
-                if (size == 6 || size == 4) {
-                    uint8_t tmp[3];
-                    int j;
-
-                    for (i = 0; i < PALETTE_SIZE; i++) {
-                        for (j = 0; j < 3; j++) {
-                            int t = (ctx->pal[i] >> (16 - j * 8)) & 0xFF;
-                            tmp[j] = av_clip_uint8((t * 129 + ctx->delta_pal[i * 3 + j]) >> 7);
-                        }
-                        ctx->pal[i] = 0xFFU << 24 | AV_RB24(tmp);
-                    }
-                } else {
-                    if (size < PALETTE_DELTA * 2 + 4) {
-                        av_log(avctx, AV_LOG_ERROR,
-                               "Incorrect palette change block size %"PRIu32".\n",
-                               size);
-                        return AVERROR_INVALIDDATA;
-                    }
-                    bytestream2_skipu(&ctx->gb, 4);
-                    for (i = 0; i < PALETTE_DELTA; i++)
-                        ctx->delta_pal[i] = bytestream2_get_le16u(&ctx->gb);
-                    if (size >= PALETTE_DELTA * 5 + 4) {
-                        for (i = 0; i < PALETTE_SIZE; i++)
-                            ctx->pal[i] = 0xFFU << 24 | bytestream2_get_be24u(&ctx->gb);
-                    } else {
-                        memset(ctx->pal, 0, sizeof(ctx->pal));
-                    }
-                }
+                if (ret = process_xpal(ctx, size))
+                    return ret;
                 break;
             case MKBETAG('S', 'T', 'O', 'R'):
                 to_store = 1;