[SDL] Fixing SDL_UnlockSurface in IE10/IE11.

Previously, just calling SDL_UnlockSurface in IE10/IE11 would throw an exception, since Emscripten assumed that the ImageData's `data` property was Uint8ClampedArray, which has a backing buffer.

IE10/IE11 still uses the deprecated CanvasPixelArray, which does not have a backing buffer property:
https://developer.mozilla.org/en-US/docs/Web/API/CanvasPixelArray

I've added an additional path to SDL_UnlockSurface for these browsers.

2 files changed, 22 insertions, 6 deletions

diff --git a/src/library_sdl.js b/src/library_sdl.js
index 1c1e8107..78f6a628 100644
--- a/src/library_sdl.js
+++ b/src/library_sdl.js
@@ -1056,14 +1056,28 @@ var LibrarySDL = {
       var buffer = surfData.buffer;
 #if USE_TYPED_ARRAYS == 2
       assert(buffer % 4 == 0, 'Invalid buffer offset: ' + buffer);
-      var src = buffer >> 2;
+      var src;
       var dst = 0;
       var isScreen = surf == SDL.screen;
-      var data32 = new Uint32Array(data.buffer);
-      var num = data32.length;
-      while (dst < num) {
-        // HEAP32[src++] is an optimization. Instead, we could do {{{ makeGetValue('buffer', 'dst', 'i32') }}};
-        data32[dst++] = HEAP32[src++] | (isScreen ? 0xff000000 : 0);
+      var num;
+      if (typeof CanvasPixelArray !== 'undefined' && data instanceof CanvasPixelArray) {
+        // IE10/IE11: Canvases are backed by the deprecated CanvasPixelArray,
+        // not UInt8ClampedArray. These don't have buffers, so we need to revert
+        // to copying a byte at a time. We do the undefined check because modern
+        // browsers do not define CanvasPixelArray anymore.
+        src = buffer;
+        num = data.length;
+        while (dst < num) {
+          data[dst++] = HEAP8[src++];
+        }
+      } else {
+        var data32 = new Uint32Array(data.buffer);
+        src = buffer >> 2;
+        num = data32.length;
+        while (dst < num) {
+          // HEAP32[src++] is an optimization. Instead, we could do {{{ makeGetValue('buffer', 'dst', 'i32') }}};
+          data32[dst++] = HEAP32[src++] | (isScreen ? 0xff000000 : 0);
+        }
       }
 #else
       var num = surfData.image.data.length;
diff --git a/tests/sdl_canvas.c b/tests/sdl_canvas.c
index 6bd659b8..cab48985 100644
--- a/tests/sdl_canvas.c
+++ b/tests/sdl_canvas.c
@@ -62,6 +62,8 @@ int main(int argc, char **argv) {
 
   printf("you should see two lines of text in different colors and a blue rectangle\n");
 
+  SDL_UnlockSurface(screen);
+  
   SDL_Quit();
 
   printf("done.\n");