swscale/swscale: Factor bottom to top handling

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libswscale/swscale.c

@@ -761,6 +761,12 @@ int attribute_align_arg sws_scale(struct SwsContext *c,
     uint8_t *dst2[4];
     uint8_t *rgb0_tmp = NULL;
     int macro_height = isBayer(c->srcFormat) ? 2 : (1 << c->chrSrcVSubSample);
+    // copy strides, so they can safely be modified
+    int srcStride2[4] = { srcStride[0], srcStride[1], srcStride[2],
+                            srcStride[3] };
+    int dstStride2[4] = { dstStride[0], dstStride[1], dstStride[2],
+                            dstStride[3] };
+    int srcSliceY_internal = srcSliceY;
 
     if (!srcStride || !dstStride || !dst || !srcSlice) {
         av_log(c, AV_LOG_ERROR, "One of the input parameters to sws_scale() is NULL, please check the calling code\n");
@@ -943,30 +949,12 @@ int attribute_align_arg sws_scale(struct SwsContext *c,
         for (i = 0; i < 4; i++)
             memset(c->dither_error[i], 0, sizeof(c->dither_error[0][0]) * (c->dstW+2));
 
-
-    // copy strides, so they can safely be modified
-    if (c->sliceDir == 1) {
-        // slices go from top to bottom
-        int srcStride2[4] = { srcStride[0], srcStride[1], srcStride[2],
-                              srcStride[3] };
-        int dstStride2[4] = { dstStride[0], dstStride[1], dstStride[2],
-                              dstStride[3] };
-
-        reset_ptr(src2, c->srcFormat);
-        reset_ptr((void*)dst2, c->dstFormat);
-
-        /* reset slice direction at end of frame */
-        if (srcSliceY + srcSliceH == c->srcH)
-            c->sliceDir = 0;
-
-        ret = c->swscale(c, src2, srcStride2, srcSliceY, srcSliceH, dst2,
-                          dstStride2);
-    } else {
+    if (c->sliceDir != 1) {
         // slices go from bottom to top => we flip the image internally
-        int srcStride2[4] = { -srcStride[0], -srcStride[1], -srcStride[2],
-                              -srcStride[3] };
-        int dstStride2[4] = { -dstStride[0], -dstStride[1], -dstStride[2],
-                              -dstStride[3] };
+        for (i=0; i<4; i++) {
+            srcStride2[i] *= -1;
+            dstStride2[i] *= -1;
+        }
 
         src2[0] += (srcSliceH - 1) * srcStride[0];
         if (!usePal(c->srcFormat))
@@ -978,16 +966,15 @@ int attribute_align_arg sws_scale(struct SwsContext *c,
         dst2[2] += ((c->dstH >> c->chrDstVSubSample) - 1) * dstStride[2];
         dst2[3] += ( c->dstH                         - 1) * dstStride[3];
 
-        reset_ptr(src2, c->srcFormat);
-        reset_ptr((void*)dst2, c->dstFormat);
-
-        /* reset slice direction at end of frame */
-        if (!srcSliceY)
-            c->sliceDir = 0;
-
-        ret = c->swscale(c, src2, srcStride2, c->srcH-srcSliceY-srcSliceH,
-                          srcSliceH, dst2, dstStride2);
+        srcSliceY_internal = c->srcH-srcSliceY-srcSliceH;
     }
+    reset_ptr(src2, c->srcFormat);
+    reset_ptr((void*)dst2, c->dstFormat);
+
+    /* reset slice direction at end of frame */
+    if (srcSliceY_internal + srcSliceH == c->srcH)
+        c->sliceDir = 0;
+    ret = c->swscale(c, src2, srcStride2, srcSliceY_internal, srcSliceH, dst2, dstStride2);
 
 
     if (c->dstXYZ && !(c->srcXYZ && c->srcW==c->dstW && c->srcH==c->dstH)) {