From 027151ca6c373de9ef25de36b333d1285de71095 Mon Sep 17 00:00:00 2001
From: Pascal Massimino <pascal.massimino@gmail.com>
Date: Wed, 8 Feb 2017 16:34:57 +0100
Subject: [PATCH] don't erase the surface before blitting.

It's done at HTML level with canvas.clearRect()

BUG=webp:261

Change-Id: I83c73791f5922cd1f426f19faf856fa1cf8f0311
---
 extras/webp_to_sdl.c | 4 ++--
 webp_js/index.html   | 7 +++++--
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/extras/webp_to_sdl.c b/extras/webp_to_sdl.c
index b47c1e6e..461d4c72 100755
--- a/extras/webp_to_sdl.c
+++ b/extras/webp_to_sdl.c
@@ -60,6 +60,7 @@ int WebpToSDL(const char* data, unsigned int data_size) {
                                  0x0000ff00u,   // G mask
                                  0x00ff0000u,   // B mask
                                  0xff000000u);  // A mask
+
   if (surface == NULL) {
     fprintf(stderr, "Unable to create %dx%d RGBA surface!\n",
             input->width, input->height);
@@ -86,8 +87,7 @@ int WebpToSDL(const char* data, unsigned int data_size) {
   }
 
   if (SDL_MUSTLOCK(surface)) SDL_UnlockSurface(surface);
-  if (SDL_FillRect(screen, &screen->clip_rect, 0xffffffff) ||
-      SDL_BlitSurface(surface, NULL, screen, NULL) ||
+  if (SDL_BlitSurface(surface, NULL, screen, NULL) ||
       SDL_Flip(screen)) {
     goto Error;
   }
diff --git a/webp_js/index.html b/webp_js/index.html
index 096ef151..3ac9325f 100644
--- a/webp_js/index.html
+++ b/webp_js/index.html
@@ -21,8 +21,11 @@ function init() {
 
 function decode(webp_data, canvas_id) {
   // get the canvas to decode into
-  Module.canvas = document.getElementById(canvas_id);
-  if (Module.canvas == null) return;
+  var canvas = document.getElementById(canvas_id);
+  if (canvas == null) return;
+  // clear previous picture (if any)
+  Module.canvas = canvas;
+  canvas.getContext('2d').clearRect(0, 0, canvas.width, canvas.height);
   // decode and measure timing
   start = new Date();
   var ret = WebpToCanvas(webp_data, webp_data.length);