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Old 08-06-2006, 09:50 PM   #1
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Join Date: May 2006
Posts: 25
Default dynamic-gradient mask acts like rectangle


I'm trying to:

1) draw a gradient with code
2) use it as a mask on a bitmap

the masked bitmap is embedded and instantiated: new EmbeddedClass()
the mask is created via a new Shape()
that Shape uses the graphics object methods to draw it: beginGradientFill, draw Rect, etc.
the gradient has an alphas array like this: [0, 255], so it goes from visible to invisible (I've checked this)
the actual masking: maskedBitmap.mask=maskShape;

the result is a solid mask, not a gradient mask...how can I apply a dynamic gradient mask?

the code is not pretty but here it goes:

package {
	import flash.display.Bitmap;
	import flash.display.BitmapData;
	import flash.display.BitmapDataChannel;
	import flash.display.DisplayObject;
	import flash.display.InterpolationMethod;
	import flash.display.Shape;
	import flash.display.SpreadMethod;
	import flash.display.Sprite;
	import flash.events.Event;
	import flash.filters.DisplacementMapFilter;
	import flash.geom.Matrix;
	import flash.geom.Point;

	public class TestIt extends Sprite
		[Embed(source="images/desert.jpg")] internal var Desert:Class;
		internal var picture:Bitmap;
		internal var rippleMap:BitmapData
		internal var rippleFilter:DisplacementMapFilter;
		internal var offset:Point;
		internal var bandMask:Shape;
		internal var bgPicture:Bitmap;
		public function TestIt()
		//put embedded picture in a bitmap
		picture= new Desert();
		//clone a background for when the foreground picture is partly masked
		bgPicture=new Bitmap(picture.bitmapData.clone());
		//create a displacement map based on blue, with a lot of noise along y
		rippleMap=new BitmapData(picture.width, picture.height/2);
		rippleFilter=new DisplacementMapFilter(rippleMap, new Point(0,50), 100, BitmapDataChannel.BLUE, 0, 55, "clamp", 0, 0);
		//listen to enterframe and animate the filter by continously offsetting the filter's displacement map's perlin noise
		addEventListener(Event.ENTER_FRAME, makeRipple) 
		offset=new Point(0,0);
		//create a gradient to use as a mask
		bandMask=new Shape();
		var colors:Array=[0xffffff, 0x0000FF];
        var alphas:Array=[100,0];
        var ratios:Array=[0, 255];
        var spread:String=SpreadMethod.PAD;
        var inter:String=InterpolationMethod.LINEAR_RGB;
        var focal:int=0
        var mat:Matrix=new Matrix();
        mat.createGradientBox(640, 200, -Math.PI/2);
  	    bandMask.graphics.beginGradientFill("linear",colors,alphas,ratios,mat, spread, inter, focal);
		bandMask.graphics.drawRect(0, 50, 640,200)
		//put the mask on the display list and mask the picture
		addChild (bandMask);
		internal function makeRipple(evt:Event):void {
			//move the first octave of the perlin noise
			rippleMap.perlinNoise(150,20, 5, 89, true, true, BitmapDataChannel.BLUE, false, [offset]);
basically, I'm using the DisplacementMapFilter to make heat rise from the horizon in the desert, but I'd like the ripples to fade out gradually into the sky by using a gradient mask

I'm considering alternatives, like merging the gradient right onto the displacement map (to fade the perlin noise gradually wherever I want)

that would probably be easier on the processer, less alphaing, but still, I'd like to know how to get a dynamic gradient mask working
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