From 273a12a013339d4b1c337a5ad8332ff97afa2022 Mon Sep 17 00:00:00 2001
From: Pascal Massimino <pascal.massimino@gmail.com>
Date: Mon, 5 Dec 2011 08:37:55 -0800
Subject: [PATCH] fix off-by-1 diff in case cropping and simple filtering

Change-Id: I6dea172d0cf129f9986b8a3e1eea85fa97a70402
---
 src/dec/frame.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/dec/frame.c b/src/dec/frame.c
index 1bf3e070..00c735af 100644
--- a/src/dec/frame.c
+++ b/src/dec/frame.c
@@ -480,8 +480,13 @@ VP8StatusCode VP8EnterCritical(VP8Decoder* const dec, VP8Io* const io) {
       dec->tl_mb_y_ = 0;
     } else {
       // For simple filter, we can filter only the cropped region.
-      dec->tl_mb_y_ = io->crop_top >> 4;
-      dec->tl_mb_x_ = io->crop_left >> 4;
+      // We include 'extra_pixels' on the other side of the boundary, since
+      // vertical or horizontal filtering of the previous macroblock can
+      // modify some abutting pixels.
+      dec->tl_mb_x_ = (io->crop_left - extra_pixels) >> 4;
+      dec->tl_mb_y_ = (io->crop_top - extra_pixels) >> 4;
+      if (dec->tl_mb_x_ < 0) dec->tl_mb_x_ = 0;
+      if (dec->tl_mb_y_ < 0) dec->tl_mb_y_ = 0;
     }
     // We need some 'extra' pixels on the right/bottom.
     dec->br_mb_y_ = (io->crop_bottom + 15 + extra_pixels) >> 4;