While cruising the internet today looking for interesting things to try out, I ran across this fun little GPU Gem about creating a post-process volumetric lighting effect. With a little bit of work I quickly ported it over to an AGAL shader (you can see it on Wonderfl here). Then I figured what the hell, why not make it into a Starling filter.

I should say right off the bat that this won’t work in ‘baseline constrained’ mode (i.e. no mobile apps), but if you’re working on a web or desktop project, this filter will give you an effect like this.

The entire filter is below. Enjoy.

 

/** * Copyright (c) 2013 Devon O. Wolfgang * * Permission is hereby granted, free of charge, to any person obtaining a copy * of this software and associated documentation files (the "Software"), to deal * in the Software without restriction, including without limitation the rights * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell * copies of the Software, and to permit persons to whom the Software is * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN * THE SOFTWARE. */ package starling.filters { import flash.display3D.Context3D; import flash.display3D.Context3DBlendFactor; import flash.display3D.Context3DProgramType; import flash.display3D.Program3D; import starling.textures.Texture; /** * Creates a 'God Rays' / fake volumetric light filter effect. Only use with Context3DProfile.BASELINE (not compatible with constrained profile) * @author Devon O. */ public class GodRaysFilter extends FragmentFilter { private var shaderProgram:Program3D; private var numSteps:int; // lightx, lighty private var lightPos:Vector. = Vector.( [ .5, .5, 1, 1 ]); // numsamples, density, numsamples * density, 1 / numsamples * density private var values1:Vector. = Vector.( [ 1, 1, 1, 1 ]); // weight, decay, exposure private var values2:Vector. = Vector.( [ 1, 1, 1, 1 ]); private var _lightX:Number = 0; private var _lightY:Number = 0; private var _weight:Number = .50; private var _decay:Number = .87; private var _exposure:Number = .35; private var _density:Number = 2.0; public function GodRaysFilter(numSteps:int = 30) { this.numSteps = numSteps; } public override function dispose():void { if (this.shaderProgram) this.shaderProgram.dispose(); super.dispose(); } protected override function createPrograms():void { var frag:String = ""; // Calculate vector from pixel to light source in screen space. frag += "sub ft0.xy, v0.xy, fc0.xy \n"; // Divide by number of samples and scale by control factor. frag += "mul ft0.xy, ft0.xy, fc1.ww \n"; // Store initial sample. frag += "tex ft1, v0, fs0 <2d, clamp, linear, mipnone> \n"; // Set up illumination decay factor. frag += "mov ft2.x, fc0.w \n"; // Store the texcoords frag += "mov ft4.xy, v0.xy \n"; for (var i:int = 0; i < this.numSteps; i++) { // Step sample location along ray. frag += "sub ft4.xy, ft4.xy, ft0.xy \n"; // Retrieve sample at new location. frag += "tex ft3, ft4.xy, fs0 <2d, clamp, linear, mipnone> \n"; // Apply sample attenuation scale/decay factors. frag += "mul ft2.y, ft2.x, fc2.x \n"; frag += "mul ft3.xyz, ft3.xyz, ft2.yyy \n"; // Accumulate combined color. frag += "add ft1.xyz, ft1.xyz, ft3.xyz \n"; // Update exponential decay factor. frag += "mul ft2.x, ft2.x, fc2.y \n"; } // Output final color with a further scale control factor. frag += "mul ft1.xyz, ft1.xyz, fc2.zzz \n"; frag += "mov oc, ft1"; this.shaderProgram = assembleAgal(frag); } protected override function activate(pass:int, context:Context3D, texture:Texture):void { // light position this.lightPos[0] = this._lightX / texture.width; this.lightPos[1] = this._lightY / texture.height; // numsamples, density, numsamples * density, 1 / numsamples * density this.values1[0] = this.numSteps; this.values1[1] = this._density; this.values1[2] = this.numSteps * values1[1]; this.values1[3] = 1 / values1[2]; // weight, decay, exposure this.values2[0] = this._weight; this.values2[1] = this._decay; this.values2[2] = this._exposure; context.setProgramConstantsFromVector(Context3DProgramType.FRAGMENT, 0, this.lightPos, 1 ); context.setProgramConstantsFromVector(Context3DProgramType.FRAGMENT, 1, this.values1, 1 ); context.setProgramConstantsFromVector(Context3DProgramType.FRAGMENT, 2, this.values2, 1 ); context.setProgram(this.shaderProgram); } public function set lightX(value:Number):void { this._lightX = value; } public function get lightX():Number { return this._lightX; } public function set lightY(value:Number):void { this._lightY = value; } public function get lightY():Number { return this._lightY; } public function set decay(value:Number):void { this._decay = value; } public function get decay():Number { return this._decay; } public function set exposure(value:Number):void { this._exposure = value; } public function get exposure():Number { return this._exposure; } public function set weight(value:Number):void { this._weight = value; } public function get weight():Number { return this._weight; } public function set density(value:Number):void { this._density = value; } public function get density():Number { return this._density; } } }