Fix entire surface alpha blending with SDL_SetAlpha

2 files changed, 4 insertions, 0 deletions

diff --git a/AUTHORS b/AUTHORS
index 5b4ee949..d8f9da02 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -98,4 +98,5 @@ a license to everyone to use it as detailed in LICENSE.)
 * Ranger Harke <ranger.harke@autodesk.com> (copyright owned by Autodesk, Inc.)
 * Tobias Vrinssen <tobias@vrinssen.de>
 * Patrick R. Martin <patrick.martin.r@gmail.com>
+* Richard Quirk <richard.quirk@gmail.com>
 
diff --git a/src/library_sdl.js b/src/library_sdl.js
index d6473df0..63e8b2b1 100644
--- a/src/library_sdl.js
+++ b/src/library_sdl.js
@@ -1131,7 +1131,10 @@ var LibrarySDL = {
     } else {
       dr = { x: 0, y: 0, w: -1, h: -1 };
     }
+    var oldAlpha = dstData.ctx.globalAlpha;
+    dstData.ctx.globalAlpha = srcData.alpha/255;
     dstData.ctx.drawImage(srcData.canvas, sr.x, sr.y, sr.w, sr.h, dr.x, dr.y, sr.w, sr.h);
+    dstData.ctx.globalAlpha = oldAlpha;
     if (dst != SDL.screen) {
       // XXX As in IMG_Load, for compatibility we write out |pixels|
       console.log('WARNING: copying canvas data to memory for compatibility');