use video pixel buffer for raycasting

src/objects.js

@@ -2104,19 +2104,12 @@ SpriteMorph.prototype.getImageData = function () {
         ).data;
         this.imageData = {
             version : this.version,
-            pixels : new Uint32Array(imageData.buffer.slice(0)),
-            full : imageData // +++ get rid of this
+            pixels : new Uint32Array(imageData.buffer.slice(0))
         };
     }
     return this.imageData.pixels;
 };
 
-SpriteMorph.prototype.getFullImageData = function () {
-    // temporary hack for raycasting. // +++
-    this.getImageData();
-    return this.imageData.full;
-};
-
 SpriteMorph.prototype.projectionSnap = function() {
     var stage = this.parentThatIsA(StageMorph),
         center = this.center().subtract(stage.position())

src/threads.js

@@ -4933,13 +4933,13 @@ Process.prototype.reportDistanceFacing = function (name) {
 */
 
     width = Math.floor(targetBounds.width() / stage.scale); // +++
-    imageData = thatObj.getFullImageData(); // +++
+    imageData = thatObj.getImageData(); // +++
 
     // scan the ray along the coordinates of a Bresenham line
     // for the first opaque pixel
     function alphaAt(imageData, width, x, y) {
-        var idx = (y * width * 4) + x * 4;
-        return imageData[idx + 3];
+        var idx = y * width + x;
+        return imageData[idx] && 0x000000FF; // alpha
     }
 
     function isOpaque(x, y) {