After Effects script for generating long shadow effects that've become so popular lately.

longShadows01.jsx

{
     //Begin undo group
	app.beginUndoGroup("Long Shadows");
    
	/* Variables */
	// Selected Comp
	var rootComp = app.project.activeItem;
	// Actual footage layer that the shadow is applied to
	var footageLayer;
	// Name of original footage layer
	var footageLayerName;
	// Outer precomp of footageLayer
	var precomposedFootage;
	// Inner shadow precomp
	var shadowSpin;
	// Outer shadow precomp
	var shadow;
	var shadowInitialWidth;
	var shadowInitialHeight;
	// Layer with effects that control all shadows in the scene
	var globalShadowControls;

	function main () {
		//Check to see if a single layer is selected
		if(rootComp.selectedLayers.length != 1)
		{
			alert("Please select ONE footage layer.");
			return;
		}

		// Get the footage layer
		footageLayer = rootComp.selectedLayers[0];
		footageLayerName = footageLayer.name;

		// Check to see if globalShadowControls exists. If not, create it and add the proper effects.
		var hasGlobalControls = false;
		for (var i = 0; i < rootComp.layers.length; i++) {
			if (rootComp.layers[i+1].name === "globalShadowControls") {
				hasGlobalControls = true;
				globalShadowControls = rootComp.layers[i+1];
			}
		}
		if (!hasGlobalControls) {
			globalShadowControls = rootComp.layers.addNull();
			globalShadowControls.name = "globalShadowControls";
			var slider = globalShadowControls("Effects").addProperty("ADBE Slider Control");
			slider.name = "Shadow Length";
			slider.property(1).setValue(100);
			var angleControl = globalShadowControls("Effects").addProperty("ADBE Angle Control");
			angleControl.name = "Global Light Direction";
			var transparency = globalShadowControls("Effects").addProperty("ADBE Slider Control");
			transparency.name = "Transparency";
			transparency.property(1).setValue(17);
		}

		// Precompose the footage layer
		var precomposedFootageIndex = footageLayer.index;
		precomposedFootage = rootComp.layers.precompose([footageLayer.index], (footageLayer.name + "-FOOTAGE"), true);
		var precomposedFootageLayer = rootComp.layers[precomposedFootageIndex];
		
		// Duplicate precomp. Call duplicate "shadow-spin"
		shadowSpin = precomposedFootage.duplicate();
		shadowSpin.name = footageLayerName + "-SHADOW_SPIN";
		var shadowSpinLayer = rootComp.layers.add(shadowSpin);
		shadowSpinLayer.moveAfter(precomposedFootageLayer);

		// Precompose "shadow-spin" in "shadow"
		shadow = rootComp.layers.precompose([shadowSpinLayer.index], (footageLayerName + "-SHADOW"), true);
		
		// Change size of "shadow" to 4000x4000
		shadowInitialHeight = shadow.height;
		shadowInitialWidth = shadow.width;
		shadow.height = 4000;
		shadow.width = 4000;
		for (var j = 0; j < shadow.layers.length; j++) {
			var layerXPos = shadow.layers[j+1].position.value[0];
			var layerYPos = shadow.layers[j+1].position.value[1];
			shadow.layers[j+1].position.setValue([(layerXPos/shadowInitialWidth)*shadow.width,
				(layerYPos/shadowInitialHeight)*shadow.height]);
		}

		// Parent rotation of "shadow-spin" to rotation of "shadow" and invert (*-1)
		shadow.layers[1].rotation.expression = "comp(\"" + rootComp.name + "\").layer(\"" + shadow.name +
				"\").transform.rotation*-1";

		// Parent rotation of "shadow" to globalShadowControls
		var shadowLayer = rootComp.layers.byName(footageLayerName + "-SHADOW");
		shadowLayer.rotation.expression = "thisComp.layer(\"globalShadowControls\")" +
			".effect(\"Global Light Direction\")(\"Angle\")";

		// Add tint effect to "shadow-spin" and map both to white
		shadowSpinLayer = shadow.layers.byName(footageLayerName + "-SHADOW_SPIN");
		var tint = shadowSpinLayer("Effects").addProperty("Tint");
		tint.property(1).setValue([1,1,1,0]);
		tint.property(2).setValue([1,1,1,0]);

		// Add box blur effect to "shadow". Change effect to horizontal.
		var boxBlur = shadowLayer("Effects").addProperty("Box Blur");
		boxBlur.property(3).setValue(2);
		
		// Add expression to "shadow" anchor point.
		shadowLayer.anchorPoint.expression = "temp = effect(\"Box Blur\")(\"Blur Radius\");[2000-temp, 2000]";

		// Parent box blur radius to globalShadowControls.
		boxBlur("Blur Radius").expression = 'thisComp.layer("globalShadowControls").effect("Shadow Length")("Slider")';

		// Add set matte effect to "shadow," change layer to none. Set invert matte to True. Set composite matte to False.
		var setMatte = shadowLayer("Effects").addProperty("Set Matte");
		setMatte.property(1).setValue(0);
		setMatte.property(3).setValue(true);
		setMatte.property(5).setValue(false);

		// Add invert effect to "shadow".
		var invert = shadowLayer("Effects").addProperty("Invert");

		// Change blend mode of "shadow" to multiply.
		shadowLayer.blendingMode = BlendingMode.MULTIPLY;
		shadowLayer.opacity.expression = 'thisComp.layer("globalShadowControls")' + 
			'.effect("Transparency")("Slider")';

		// Add drop shadow layer style to footage
		var dropShadow = precomposedFootageLayer("Effects").addProperty("Drop Shadow");
		dropShadow.property(2).setValue(64);
		dropShadow.property(3).expression = 'thisComp.layer("globalShadowControls")' +
			'.effect("Global Light Direction")("Angle")+90';
		dropShadow.property(4).setValue(2);
		dropShadow.property(5).setValue(2);

	}

	main();

	//End Undo group
	app.endUndoGroup();
}