<snapdata remixID="8928214"><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" 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</pentrails><costumes><list 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="159.99999999999974" y="120" 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="10" y="51"><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;        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