Set and use uv_crop_[width|height]

Ensure consistent border extension by rounding uv_crop_* at image
creation time. Where it was rounded problems could arise with the right
and bottom extensions.
When padding = 32, y_width = 64, and y_crop_width = 63:
 (padding + width - crop_width + 1) / 2
 32 + 64 - 63 + 1 should equal 32 *but*
 32 + 1 + 1 equals 34 giving a right buffer of 17 instead of 16.
By calculating uv_crop_* earlier we round up at the appropriate time and
for the same values:
 (y_crop_width + 1) / 2
 63 + 1 / 2
 64
 (padding / 2) + uv_width - uv_crop_width
 16 + 16 - 16
 16

Change-Id: If866cd1b63444771440edb1432280ac83875969b

vpx_scale/generic/yv12config.c

@@ -81,6 +81,8 @@ int vp8_yv12_realloc_frame_buffer(YV12_BUFFER_CONFIG *ybf,
     ybf->y_height = aligned_height;
     ybf->y_stride = y_stride;
 
+    ybf->uv_crop_width = (width + 1) / 2;
+    ybf->uv_crop_height = (height + 1) / 2;
     ybf->uv_width = uv_width;
     ybf->uv_height = uv_height;
     ybf->uv_stride = uv_stride;

vpx_scale/generic/yv12extend.c

@@ -56,6 +56,9 @@ static void extend_plane(uint8_t *const src, int src_stride,
 }
 
 void vp8_yv12_extend_frame_borders_c(YV12_BUFFER_CONFIG *ybf) {
+  const int uv_border = ybf->border / 2;
+
+  assert(ybf->border % 2 == 0);
   assert(ybf->y_height - ybf->y_crop_height < 16);
   assert(ybf->y_width - ybf->y_crop_width < 16);
   assert(ybf->y_height - ybf->y_crop_height >= 0);
@@ -68,16 +71,16 @@ void vp8_yv12_extend_frame_borders_c(YV12_BUFFER_CONFIG *ybf) {
                ybf->border + ybf->y_width - ybf->y_crop_width);
 
   extend_plane(ybf->u_buffer, ybf->uv_stride,
-               (ybf->y_crop_width + 1) / 2, (ybf->y_crop_height + 1) / 2,
-               ybf->border / 2, ybf->border / 2,
-               (ybf->border + ybf->y_height - ybf->y_crop_height + 1) / 2,
-               (ybf->border + ybf->y_width - ybf->y_crop_width + 1) / 2);
+               ybf->uv_crop_width, ybf->uv_crop_height,
+               uv_border, uv_border,
+               uv_border + ybf->uv_height - ybf->uv_crop_height,
+               uv_border + ybf->uv_width - ybf->uv_crop_width);
 
   extend_plane(ybf->v_buffer, ybf->uv_stride,
-               (ybf->y_crop_width + 1) / 2, (ybf->y_crop_height + 1) / 2,
-               ybf->border / 2, ybf->border / 2,
-               (ybf->border + ybf->y_height - ybf->y_crop_height + 1) / 2,
-               (ybf->border + ybf->y_width - ybf->y_crop_width + 1) / 2);
+               ybf->uv_crop_width, ybf->uv_crop_height,
+               uv_border, uv_border,
+               uv_border + ybf->uv_height - ybf->uv_crop_height,
+               uv_border + ybf->uv_width - ybf->uv_crop_width);
 }
 
 #if CONFIG_VP9