optimized collision detection

by only looking at the alpha channel data

HISTORY.md

@@ -4,11 +4,15 @@
 * **New Features:**
 * **Notable Changes:**
     * gliding animation when inserting  blocks using the keyboard
+    * optimized collision detection
 * **Notable Fixes:**
     * list watchers occasionally didn't show cells after reassigning a changed list to a variable
     * FOREACH over a linked list failed for scripts mutating it
 * **Translation Updates:**
 
+### 2019-07-02
+* morphic: optimized collision detection by only looking at the alpha channel data
+
 ### 2019-07-01
 * new dev version
 * lists: fixed #2446

snap.html

@@ -4,7 +4,7 @@
         <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
         <title>Snap! Build Your Own Blocks 5.0.1 - dev -</title>
         <link rel="shortcut icon" href="src/favicon.ico">
-        <script type="text/javascript" src="src/morphic.js?version=2019-07-01"></script>
+        <script type="text/javascript" src="src/morphic.js?version=2019-07-02"></script>
         <script type="text/javascript" src="src/widgets.js?version=2019-06-27"></script>
         <script type="text/javascript" src="src/blocks.js?version=2019-07-01"></script>
         <script type="text/javascript" src="src/threads.js?version=2019-07-01"></script>

src/morphic.js

@@ -1162,7 +1162,7 @@
 
 /*global window, HTMLCanvasElement, FileReader, Audio, FileList, Map*/
 
-var morphicVersion = '2019-July-01';
+var morphicVersion = '2019-July-02';
 var modules = {}; // keep track of additional loaded modules
 var useBlurredShadows = getBlurredShadowSupport(); // check for Chrome-bug
 
@@ -4454,19 +4454,18 @@ Morph.prototype.evaluateString = function (code) {
 
 Morph.prototype.isTouching = function (otherMorph) {
     var oImg = this.overlappingImage(otherMorph),
-        data;
+        data, len, i;
     if (!oImg.width || !oImg.height) {
         return false;
     }
     data = oImg.getContext('2d')
         .getImageData(1, 1, oImg.width, oImg.height)
         .data;
-    return detect(
-        data,
-        function (each) {
-            return each !== 0;
-        }
-    ) !== null;
+    len = data.length;
+    for(i = 3; i < len; i += 4) {
+        if (data[i] !== 0) {return true; }
+    }
+    return false;
 };
 
 Morph.prototype.overlappingImage = function (otherMorph) {