Source: core/renderers/canvas/utils/CanvasMaskManager.js

var CanvasGraphics = require('./CanvasGraphics');

/**
 * A set of functions used to handle masking.
 *
 * @class
 * @memberof PIXI
 */
function CanvasMaskManager()
{}

CanvasMaskManager.prototype.constructor = CanvasMaskManager;
module.exports = CanvasMaskManager;

/**
 * This method adds it to the current stack of masks.
 *
 * @param maskData {object} the maskData that will be pushed
 * @param renderer {PIXI.WebGLRenderer|PIXI.CanvasRenderer} The renderer context to use.
 */
CanvasMaskManager.prototype.pushMask = function (maskData, renderer)
{

    renderer.context.save();

    var cacheAlpha = maskData.alpha;
    var transform = maskData.worldTransform;
    var resolution = renderer.resolution;

    renderer.context.setTransform(
        transform.a * resolution,
        transform.b * resolution,
        transform.c * resolution,
        transform.d * resolution,
        transform.tx * resolution,
        transform.ty * resolution
    );

    //TODO suport sprite alpha masks??
    //lots of effort required. If demand is great enough..
    if(!maskData.texture)
    {
        CanvasGraphics.renderGraphicsMask(maskData, renderer.context);
        renderer.context.clip();
    }

    maskData.worldAlpha = cacheAlpha;
};

/**
 * Restores the current drawing context to the state it was before the mask was applied.
 *
 * @param renderer {PIXI.WebGLRenderer|PIXI.CanvasRenderer} The renderer context to use.
 */
CanvasMaskManager.prototype.popMask = function (renderer)
{
    renderer.context.restore();
};

CanvasMaskManager.prototype.destroy = function () {};