fixed #1707 (new Chrome blitting issue)

blocks.js

@@ -150,7 +150,7 @@ CustomCommandBlockMorph*/
 
 // Global stuff ////////////////////////////////////////////////////////
 
-modules.blocks = '2017-January-13';
+modules.blocks = '2017-April-10';
 
 var SyntaxElementMorph;
 var BlockMorph;
@@ -10918,11 +10918,17 @@ ColorSlotMorph.prototype.getUserColor = function () {
     pal.setPosition(this.bottomLeft().add(new Point(0, this.edge)));
 
     hand.processMouseMove = function (event) {
+        var clr = world.getGlobalPixelColor(hand.position());
         hand.setPosition(new Point(
             event.pageX - posInDocument.x,
             event.pageY - posInDocument.y
         ));
-        myself.setColor(world.getGlobalPixelColor(hand.position()));
+        if (!clr.a) {
+            // ignore transparent,
+            // needed for retina-display support
+            return;
+        }
+        myself.setColor(clr);
     };
 
     hand.processMouseDown = nop;

gui.js

@@ -74,7 +74,7 @@ isRetinaSupported, SliderMorph, Animation*/
 
 // Global stuff ////////////////////////////////////////////////////////
 
-modules.gui = '2017-January-13';
+modules.gui = '2017-April-10';
 
 // Declarations
 
@@ -3187,7 +3187,7 @@ IDE_Morph.prototype.aboutSnap = function () {
         module, btn1, btn2, btn3, btn4, licenseBtn, translatorsBtn,
         world = this.world();
 
-    aboutTxt = 'Snap! 4.0.10\nBuild Your Own Blocks\n\n'
+    aboutTxt = 'Snap! 4.0.10.1\nBuild Your Own Blocks\n\n'
         + 'Copyright \u24B8 2017 Jens M\u00F6nig and '
         + 'Brian Harvey\n'
         + 'jens@moenig.org, bh@cs.berkeley.edu\n\n'

history.txt

@@ -3403,3 +3403,7 @@ Fixes:
 170410
 ------
 * Revert to 4.0.10 to prepare for newly surfaced bug in the Chrome browser
+* fixed #1707 (new Chrome blitting issue)
+
+== v4.0.10.1 - maintenance release - ===
+

morphic.js

@@ -1137,7 +1137,7 @@
 
 /*global window, HTMLCanvasElement, FileReader, Audio, FileList*/
 
-var morphicVersion = '2017-January-09';
+var morphicVersion = '2017-April-10';
 var modules = {}; // keep track of additional loaded modules
 var useBlurredShadows = getBlurredShadowSupport(); // check for Chrome-bug
 
@@ -11294,29 +11294,13 @@ WorldMorph.prototype.fillPage = function () {
 // WorldMorph global pixel access:
 
 WorldMorph.prototype.getGlobalPixelColor = function (point) {
+    // answer the color at the given point.
+
 /*
-    answer the color at the given point.
+    // original method, now deprecated as of 4/4/2017 because Chrome
+    // "taints" the on-screen canvas as soon as its image data is
+    // requested, significantly slowing down subsequent blittings
 
-    Note: for some strange reason this method works fine if the page is
-    opened via HTTP, but *not*, if it is opened from a local uri
-    (e.g. from a directory), in which case it's always null.
-
-    This behavior is consistent throughout several browsers. I have no
-    clue what's behind this, apparently the imageData attribute of
-    canvas context only gets filled with meaningful data if transferred
-    via HTTP ???
-
-    This is somewhat of a showstopper for color detection in a planned
-    offline version of Snap.
-
-    The issue has also been discussed at: (join lines before pasting)
-    http://stackoverflow.com/questions/4069400/
-    canvas-getimagedata-doesnt-work-when-running-locally-on-windows-
-    security-excep
-
-    The suggestion solution appears to work, since the settings are
-    applied globally.
-*/
     var dta = this.worldCanvas.getContext('2d').getImageData(
         point.x,
         point.y,
@@ -11324,6 +11308,14 @@ WorldMorph.prototype.getGlobalPixelColor = function (point) {
         1
     ).data;
     return new Color(dta[0], dta[1], dta[2]);
+*/
+
+    var clr = this.hand.morphAtPointer().getPixelColor(this.hand.position());
+    // IMPORTANT:
+    // all callers of getGlobalPixelColor should make provisions for retina
+    // display support, which gets null-pixels interlaced with non-null ones:
+    // if (!clr.a) {/* ignore */ }
+    return clr;
 };
 
 // WorldMorph events:

paint.js

@@ -63,6 +63,8 @@
     Jan 18 - avoid pixel collision detection in PaintCanvas (Jens)
     Mar 22 - fixed automatic rotation center point mechanism (Jens)
     May 10 - retina display support adjustments (Jens)
+    2017
+    April 10 - getGlobalPixelColor adjustment for Chrome & retina (Jens)
 */
 
 /*global Point, Rectangle, DialogBoxMorph, AlignmentMorph, PushButtonMorph,
@@ -73,7 +75,7 @@ StageMorph, isNil*/
 
 // Global stuff ////////////////////////////////////////////////////////
 
-modules.paint = '2016-July-14';
+modules.paint = '2017-April-10';
 
 // Declarations
 
@@ -461,6 +463,11 @@ PaintEditorMorph.prototype.getUserColor = function () {
             event.pageY - posInDocument.y
         ));
         color = world.getGlobalPixelColor(hand.position());
+        if (!color.a) {
+            // ignore transparent,
+            // needed for retina-display support
+            return;
+        }
         color.a = 255;
         myself.propertiesControls.colorpicker.action(color);
     };