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// =================================================================================================
// Starling Framework
// Copyright Gamua GmbH. All Rights Reserved.
// This program is free software. You can redistribute and/or modify it
// in accordance with the terms of the accompanying license agreement.
// =================================================================================================
package starling.display
import flash.display3D.Context3DBlendFactor;
import starling.core.Starling;
/** A class that provides constant values for visual blend mode effects.
* <p>A blend mode is always defined by two 'Context3DBlendFactor' values. A blend factor
* represents a particular four-value vector that is multiplied with the source or destination
* color in the blending formula. The blending formula is:</p>
* <pre>result = source × sourceFactor + destination × destinationFactor</pre>
* <p>In the formula, the source color is the output color of the pixel shader program. The
* destination color is the color that currently exists in the color buffer, as set by
* previous clear and draw operations.</p>
* <p>You can add your own blend modes via <code>BlendMode.register</code>.
* To get the math right, remember that all colors in Starling use premultiplied alpha (PMA),
* which means that their RGB values were multiplied with the alpha value.</p>
* @see flash.display3D.Context3DBlendFactor
public class BlendMode
private var _name:String;
private var _sourceFactor:String;
private var _destinationFactor:String;
private static var sBlendModes:Object;
/** Creates a new BlendMode instance. Don't call this method directly; instead,
* register a new blend mode using <code>BlendMode.register</code>. */
public function BlendMode(name:String, sourceFactor:String, destinationFactor:String)
_name = name;
_sourceFactor = sourceFactor;
_destinationFactor = destinationFactor;
/** Inherits the blend mode from this display object's parent. */
public static const AUTO:String = "auto";
/** Deactivates blending, i.e. disabling any transparency. */
public static const NONE:String = "none";
/** The display object appears in front of the background. */
public static const NORMAL:String = "normal";
/** Adds the values of the colors of the display object to the colors of its background. */
public static const ADD:String = "add";
/** Multiplies the values of the display object colors with the the background color. */
public static const MULTIPLY:String = "multiply";
/** Multiplies the complement (inverse) of the display object color with the complement of
* the background color, resulting in a bleaching effect. */
public static const SCREEN:String = "screen";
/** Erases the background when drawn on a RenderTexture. */
public static const ERASE:String = "erase";
/** When used on a RenderTexture, the drawn object will act as a mask for the current
* content, i.e. the source alpha overwrites the destination alpha. */
public static const MASK:String = "mask";
/** Draws under/below existing objects; useful especially on RenderTextures. */
public static const BELOW:String = "below";
// static access methods
/** Returns the blend mode with the given name.
* Throws an ArgumentError if the mode does not exist. */
public static function get(modeName:String):BlendMode
if (sBlendModes == null) registerDefaults();
if (modeName in sBlendModes) return sBlendModes[modeName];
else throw new ArgumentError("Blend mode not found: " + modeName);
/** Registers a blending mode under a certain name. */
public static function register(name:String, srcFactor:String, dstFactor:String):BlendMode
if (sBlendModes == null) registerDefaults();
var blendMode:BlendMode = new BlendMode(name, srcFactor, dstFactor);
sBlendModes[name] = blendMode;
return blendMode;
private static function registerDefaults():void
if (sBlendModes) return;
sBlendModes = {};
register("none" , Context3DBlendFactor.ONE, Context3DBlendFactor.ZERO);
register("normal", Context3DBlendFactor.ONE, Context3DBlendFactor.ONE_MINUS_SOURCE_ALPHA);
register("add", Context3DBlendFactor.ONE, Context3DBlendFactor.ONE);
register("multiply", Context3DBlendFactor.DESTINATION_COLOR, Context3DBlendFactor.ONE_MINUS_SOURCE_ALPHA);
register("screen", Context3DBlendFactor.ONE, Context3DBlendFactor.ONE_MINUS_SOURCE_COLOR);
register("erase", Context3DBlendFactor.ZERO, Context3DBlendFactor.ONE_MINUS_SOURCE_ALPHA);
register("mask", Context3DBlendFactor.ZERO, Context3DBlendFactor.SOURCE_ALPHA);
register("below", Context3DBlendFactor.ONE_MINUS_DESTINATION_ALPHA, Context3DBlendFactor.DESTINATION_ALPHA);
// instance methods / properties
/** Sets the appropriate blend factors for source and destination on the current context. */
public function activate():void
Starling.context.setBlendFactors(_sourceFactor, _destinationFactor);
/** Returns the name of the blend mode. */
public function toString():String { return _name; }
/** The source blend factor of this blend mode. */
public function get sourceFactor():String { return _sourceFactor; }
/** The destination blend factor of this blend mode. */
public function get destinationFactor():String { return _destinationFactor; }
/** Returns the name of the blend mode. */
public function get name():String { return _name; }