added new CUT FROM command to the pen category

HISTORY.md

@@ -4,6 +4,7 @@
 * **New Features:**
     * new gesture: holding the shift-key when dragging extracts a single command from a stack of blocks
     * new "extract" single command block context menu option
+    * new CUT FROM command in the pen category
     * added "pie chart" option to PLOT command in the frequency distribution analysis library
     * added getProjectXML() method to the API
     * new noCloud flag that disables cloud access, thanks, Bernat
@@ -24,6 +25,7 @@
 ### 2020-11-02
 * objects: tweaked drop-shadows for sprites
 * blocks: tweaked drop-shadows for comments
+* objects, threads: added new CUT FROM command to the pen category
 
 ### 2020-10-28
 * gui: tweaked wait-until-assets-are-loaded mechanism

snap.html

@@ -9,7 +9,7 @@
         <script src="src/symbols.js?version=2020-10-07"></script>
         <script src="src/widgets.js?version=2020-10-06"></script>
         <script src="src/blocks.js?version=2020-11-02"></script>
-        <script src="src/threads.js?version=2020-10-08"></script>
+        <script src="src/threads.js?version=2020-11-02"></script>
         <script src="src/objects.js?version=2020-11-02"></script>
         <script src="src/gui.js?version=2020-10-28"></script>
         <script src="src/paint.js?version=2020-05-17"></script>

src/objects.js

@@ -698,6 +698,11 @@ SpriteMorph.prototype.initBlocks = function () {
             category: 'pen',
             spec: 'paste on %spr'
         },
+        doCutFrom: {
+            type: 'command',
+            category: 'pen',
+            spec: 'cut from %spr'
+        },
 
         // Control
         receiveGo: {
@@ -2380,6 +2385,7 @@ SpriteMorph.prototype.blockTemplates = function (category) {
         blocks.push(block('reportPenTrailsAsCostume'));
         blocks.push('-');
         blocks.push(block('doPasteOn'));
+        blocks.push(block('doCutFrom'));
         blocks.push('=');
         blocks.push(this.makeBlockButton(cat));
 
@@ -4450,7 +4456,7 @@ SpriteMorph.prototype.changeSize = function (delta) {
 
 // SpriteMorph printing on another sprite:
 
-SpriteMorph.prototype.pasteOn = function (target) {
+SpriteMorph.prototype.blitOn = function (target, mask = 'source-atop') {
     // draw my costume onto a copy of the target's costume scaled and rotated
     // so it appears as though I'm "stamped" onto it.
 
@@ -4549,7 +4555,7 @@ SpriteMorph.prototype.pasteOn = function (target) {
     ctx = targetCostume.contents.getContext('2d');
     ctx.rotate(radians(relRot));
     ctx.scale(relScale, relScale);
-    ctx.globalCompositeOperation = 'source-atop';
+    ctx.globalCompositeOperation = mask;
     ctx.drawImage(sourceCostume.contents, pos.x, pos.y);
 
     // make the target wear the new costume
@@ -8427,6 +8433,7 @@ StageMorph.prototype.blockTemplates = function (category) {
         blocks.push(block('reportPenTrailsAsCostume'));
         blocks.push('-');
         blocks.push(block('doPasteOn'));
+        blocks.push(block('doCutFrom'));
         blocks.push('=');
         blocks.push(this.makeBlockButton(cat));
 

src/threads.js

@@ -61,7 +61,7 @@ StageMorph, SpriteMorph, StagePrompterMorph, Note, modules, isString, copy, Map,
 isNil, WatcherMorph, List, ListWatcherMorph, alert, console, TableMorph, BLACK,
 TableFrameMorph, ColorSlotMorph, isSnapObject, newCanvas, Symbol, SVG_Costume*/
 
-modules.threads = '2020-October-08';
+modules.threads = '2020-November-02';
 
 var ThreadManager;
 var Process;
@@ -4374,9 +4374,17 @@ Process.prototype.changePenHSVA = Process.prototype.changeHSVA;
 Process.prototype.setBackgroundHSVA = Process.prototype.setHSVA;
 Process.prototype.changeBackgroundHSVA = Process.prototype.changeHSVA;
 
-// Process pasting primitives
+// Process cutting & pasting primitives
 
-Process.prototype.doPasteOn = function (name, thisObj, stage) {
+Process.prototype.doPasteOn = function (name) {
+    this.blitOn(name, 'source-atop');
+};
+
+Process.prototype.doCutFrom = function (name) {
+    this.blitOn(name, 'destination-out');
+};
+
+Process.prototype.blitOn = function (name, mask, thisObj, stage) {
     // allow for lists of sprites and also check for temparary clones,
     // as in Scratch 2.0,
     var those;
@@ -4386,7 +4394,7 @@ Process.prototype.doPasteOn = function (name, thisObj, stage) {
         name = stage;
     }
     if (isSnapObject(name)) {
-        return thisObj.pasteOn(name);
+        return thisObj.blitOn(name, mask);
     }
     if (name instanceof List) { // assume all elements to be sprites
         those = name.itemsArray();
@@ -4394,7 +4402,7 @@ Process.prototype.doPasteOn = function (name, thisObj, stage) {
         those = this.getObjectsNamed(name, thisObj, stage); // clones
     }
     those.forEach(each =>
-        this.doPasteOn(each, thisObj, stage)
+        this.blitOn(each, mask, thisObj, stage)
     );
 };