From 469ba2cdfdcaaabbc0993994243646c257b3526c Mon Sep 17 00:00:00 2001
From: Pascal Massimino <pascal.massimino@gmail.com>
Date: Fri, 23 Oct 2015 00:01:24 -0700
Subject: [PATCH] vwebp: fix incorrect clipping w/NO_BLEND

when the previous frame does not specify dispose to background only the
current frame's rectangle should be cleared

related to bug #245

Change-Id: I2fc4f5be99057e0bf87d8fedec57b06859b070bd
---
 examples/vwebp.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/examples/vwebp.c b/examples/vwebp.c
index b945f6ee..bcc67da9 100644
--- a/examples/vwebp.c
+++ b/examples/vwebp.c
@@ -308,19 +308,24 @@ static void HandleDisplay(void) {
     //              they will be incorrect if the window is resized.
     // glScissor() takes window coordinates (0,0 at bottom left).
     int window_x, window_y;
+    int frame_w, frame_h;
     if (prev->dispose_method == WEBP_MUX_DISPOSE_BACKGROUND) {
       // Clear the previous frame rectangle.
       window_x = prev->x_offset;
       window_y = kParams.canvas_height - prev->y_offset - prev->height;
+      frame_w = prev->width;
+      frame_h = prev->height;
     } else {  // curr->blend_method == WEBP_MUX_NO_BLEND.
       // We simulate no-blending behavior by first clearing the current frame
       // rectangle (to a checker-board) and then alpha-blending against it.
       window_x = curr->x_offset;
       window_y = kParams.canvas_height - curr->y_offset - curr->height;
+      frame_w = curr->width;
+      frame_h = curr->height;
     }
     glEnable(GL_SCISSOR_TEST);
     // Only update the requested area, not the whole canvas.
-    glScissor(window_x, window_y, prev->width, prev->height);
+    glScissor(window_x, window_y, frame_w, frame_h);
 
     glClear(GL_COLOR_BUFFER_BIT);  // use clear color
     DrawCheckerBoard();