<snapdata remixID="8925614"><project name="U2L4-checkerboard_SV" app="Snap! 5.1, http://snap.berkeley.edu" version="1"><notes></notes><thumbnail>data:image/png;base64,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</thumbnail><stage name="Stage" width="480" height="360" costume="0" color="255,255,255,1" tempo="60" threadsafe="false" volume="100" pan="0" lines="flat" ternary="true" codify="false" inheritance="false" sublistIDs="false" scheduled="false" id="1"><pentrails>data:image/png;base64,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struct="atomic" id="2"></list></costumes><sounds><list struct="atomic" id="3"></list></sounds><variables></variables><blocks></blocks><scripts></scripts><sprites><sprite name="Sprite" idx="1" x="140" y="130" heading="90" scale="1" volume="100" pan="0" rotation="1" draggable="true" costume="0" color="8,5,0,1" pen="tip" id="8"><costumes><list struct="atomic" id="9"></list></costumes><sounds><list struct="atomic" id="10"></list></sounds><blocks></blocks><variables></variables><scripts><script x="63" y="142"><custom-block s="draw checkerboard"></custom-block></script></scripts></sprite></sprites></stage><hidden></hidden><headers></headers><code></code><blocks><block-definition s="set flag %&apos;which&apos; to %&apos;tf&apos;" type="command" category="sensing"><header></header><code></code><translations></translations><inputs><input type="%s" readonly="true"><options>Presentation mode&#xD;Retina display support&#xD;Long form input dialog&#xD;Plain prototype labels&#xD;Input sliders&#xD;Execute on slider change&#xD;Clicking sound&#xD;Turbo mode&#xD;Flat design&#xD;Keyboard editing&#xD;Table support&#xD;Table lines&#xD;Visible stepping&#xD;Thread safe scripts&#xD;Prefer smooth animations&#xD;Flat line ends&#xD;Codification support&#xD;Inheritance support</options></input><input type="%b"></input></inputs><script><block s="doRun"><block s="reportJSFunction"><list><l>which</l><l>tf</l></list><l>var   stage = this.parentThatIsA(StageMorph),&#xD;        ide = stage.parentThatIsA(IDE_Morph),&#xD;        world = stage.parentThatIsA(WorldMorph);&#xD;&#xD;if (tf != !!tf) return;&#xD;&#xD;try{&#xD;ide.savingPreferences = false;&#xD;&#xD;switch (which) {&#xD;    case &apos;Presentation mode&apos;:&#xD;        if (tf != ide.isAppMode) ide.toggleAppMode();&#xD;        break;&#xD;    case &apos;Retina display support&apos;:&#xD;        if (tf != isRetinaEnabled()) ide.toggleRetina();&#xD;        break;&#xD;    case &apos;Long form input dialog&apos;:&#xD;        if (tf != InputSlotDialogMorph.prototype.isLaunchingExpanded)&#xD;            ide.toggleLongFormInputDialog();&#xD;        break;&#xD;    case &apos;Plain prototype labels&apos;:&#xD;        if (tf != BlockLabelPlaceHolderMorph.prototype.plainLabel)&#xD;            ide.togglePlainPrototypeLabels();&#xD;        break;&#xD;    case &apos;Input sliders&apos;:&#xD;        MorphicPreferences.useSliderForInput = tf;&#xD;        break;&#xD;    case &apos;Execute on slider change&apos;:&#xD;        ArgMorph.prototype.executeOnSliderEdit = tf;&#xD;        break;&#xD;    case &apos;Clicking sound&apos;:&#xD;        if (tf != !!BlockMorph.prototype.snapSound)&#xD;            BlockMorph.prototype.toggleSnapSound();&#xD;        break;&#xD;    case &apos;Turbo mode&apos;:&#xD;        if (tf != stage.isFastTracked)&#xD;            ide.toggleFastTracking();&#xD;        break;&#xD;    case &apos;Flat design&apos;:&#xD;        if (tf == MorphicPreferences.isFlat) break;&#xD;        if (tf)&#xD;            ide.flatDesign();&#xD;        else&#xD;            ide.defaultDesign();&#xD;        break;&#xD;    case &apos;Keyboard editing&apos;:&#xD;            ScriptsMorph.prototype.enableKeyboard = tf;&#xD;        break;&#xD;    case &apos;Table support&apos;:&#xD;            List.prototype.enableTables = tf;&#xD;        break;&#xD;    case &apos;Table lines&apos;:&#xD;                TableMorph.prototype.highContrast = tf;&#xD;        break;&#xD;    case &apos;Visible stepping&apos;:&#xD;        if (tf != Process.prototype.enableSingleStepping)&#xD;            ide.toggleSingleStepping();&#xD;        break;&#xD;    case &apos;Thread safe scripts&apos;:&#xD;        stage.isThreadSafe = tf;&#xD;        break;&#xD;    case &apos;Prefer smooth animations&apos;:&#xD;        if (tf != (StageMorph.prototype.frameRate &gt; 0))&#xD;            ide.toggleVariableFrameRate();&#xD;        break;&#xD;    case &apos;Flat line ends&apos;:&#xD;        SpriteMorph.prototype.useFlatLineEnds = tf;&#xD;        break;&#xD;    case &apos;Codification support&apos;:&#xD;        if (tf != StageMorph.prototype.enableCodeMapping) {&#xD;            StageMorph.prototype.enableCodeMapping = tf;&#xD;            ide.currentSprite.blocksCache.variables = null;&#xD;            ide.currentSprite.paletteCache.variables = null;&#xD;            ide.refreshPalette();&#xD;        }&#xD;        break;&#xD;    case &apos;Inheritance support&apos;:&#xD;        if (tf != StageMorph.prototype.enableInheritance) {&#xD;            StageMorph.prototype.enableInheritance = tf;&#xD;            ide.currentSprite.blocksCache.variables = null;&#xD;            ide.currentSprite.paletteCache.variables = null;&#xD;            ide.refreshPalette();&#xD;        }&#xD;        break;&#xD;};&#xD;}&#xD;finally {&#xD;ide.savingPreferences = false;&#xD;};&#xD;</l></block><list><block var="which"/><block var="tf"/></list></block></script></block-definition><block-definition s="draw brick, length: %&apos;length&apos; width: 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