<snapdata remixID="8927190"><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="-150" y="-170" heading="90" scale="1" volume="100" pan="0" rotation="1" draggable="true" costume="0" color="255,47,31,1" 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="23" y="10"><block s="clear"></block></script><script x="67" y="392.99999999999994"><custom-block s="draw black square size %n"><l>50</l></custom-block><custom-block s="draw red square size %n"><l>50</l></custom-block></script><script x="137" y="44"><custom-block s="DrawCheckerboard"></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: %&apos;width&apos;" type="command" category="pen"><header></header><code></code><translations></translations><inputs><input type="%n"></input><input type="%n"></input></inputs><script><block s="setColor"><color>145,26,68,1</color></block><custom-block s="set flat line ends to %b"><block s="reportBoolean"><l><bool>true</bool></l></block></custom-block><block s="setSize"><block var="width"/></block><block s="down"></block><block s="forward"><block var="length"/></block><block s="up"></block></script></block-definition><block-definition s="set flat line ends to %&apos;flag&apos;" type="command" category="pen"><header></header><code></code><translations></translations><inputs><input type="%b"></input></inputs><script><custom-block s="set flag %s to %b"><l>Flat line ends</l><block var="flag"/></custom-block></script></block-definition><block-definition s="draw black square size %&apos;size&apos;" type="command" category="pen"><header></header><code></code><translations></translations><inputs><input type="%n"></input></inputs><script><block s="setColor"><color>8,5,0,1</color></block><custom-block s="set flat line ends to %b"><block s="reportBoolean"><l><bool>true</bool></l></block></custom-block><block s="setSize"><block var="size"/></block><block s="down"></block><block s="forward"><block var="size"/></block><block s="up"></block></script></block-definition><block-definition s="draw red square size %&apos;size&apos;" type="command" category="pen"><header></header><code></code><translations></translations><inputs><input type="%n"></input></inputs><script><block s="setColor"><color>255,47,31,1</color></block><custom-block s="set flat line ends to %b"><block s="reportBoolean"><l><bool>true</bool></l></block></custom-block><block 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