# Source: src/pixi/renderers/webgl/utils/WebGLSpriteBatch.js

    /**
     * @author Mat Groves
     *
     * Big thanks to the very clever Matt DesLauriers <mattdesl> https://github.com/mattdesl/
     * for creating the original pixi version!
     * Also a thanks to https://github.com/bchevalier for tweaking the tint and alpha so that they now share 4 bytes on the vertex buffer
     *
     * Heavily inspired by LibGDX's WebGLSpriteBatch:
     * https://github.com/libgdx/libgdx/blob/master/gdx/src/com/badlogic/gdx/graphics/g2d/WebGLSpriteBatch.java
     */

     /**
     *
     * @class WebGLSpriteBatch
     * @private
     * @constructor
     */
    PIXI.WebGLSpriteBatch = function()
    {
        /**
         * @property vertSize
         * @type Number
         */
        this.vertSize = 5;

        /**
         * The number of images in the SpriteBatch before it flushes
         * @property size
         * @type Number
         */
        this.size = 2000;//Math.pow(2, 16) /  this.vertSize;

        //the total number of bytes in our batch
        var numVerts = this.size * 4 * 4 * this.vertSize;
        //the total number of indices in our batch
        var numIndices = this.size * 6;

        /**
        * Holds the vertices
        *
        * @property vertices
        * @type ArrayBuffer
        */
        this.vertices = new PIXI.ArrayBuffer(numVerts);

        /**
        * View on the vertices as a Float32Array
        *
        * @property positions
        * @type Float32Array
        */
        this.positions = new PIXI.Float32Array(this.vertices);

        /**
        * View on the vertices as a Uint32Array
        *
        * @property colors
        * @type Uint32Array
        */
        this.colors = new PIXI.Uint32Array(this.vertices);

        /**
         * Holds the indices
         *
         * @property indices
         * @type Uint16Array
         */
        this.indices = new PIXI.Uint16Array(numIndices);

        /**
         * @property lastIndexCount
         * @type Number
         */
        this.lastIndexCount = 0;

        for (var i=0, j=0; i < numIndices; i += 6, j += 4)
        {
            this.indices[i + 0] = j + 0;
            this.indices[i + 1] = j + 1;
            this.indices[i + 2] = j + 2;
            this.indices[i + 3] = j + 0;
            this.indices[i + 4] = j + 2;
            this.indices[i + 5] = j + 3;
        }

        /**
         * @property drawing
         * @type Boolean
         */
        this.drawing = false;

        /**
         * @property currentBatchSize
         * @type Number
         */
        this.currentBatchSize = 0;

        /**
         * @property currentBaseTexture
         * @type BaseTexture
         */
        this.currentBaseTexture = null;

        /**
         * @property dirty
         * @type Boolean
         */
        this.dirty = true;

        /**
         * @property textures
         * @type Array
         */
        this.textures = [];

        /**
         * @property blendModes
         * @type Array
         */
        this.blendModes = [];

        /**
         * @property shaders
         * @type Array
         */
        this.shaders = [];

        /**
         * @property sprites
         * @type Array
         */
        this.sprites = [];

        /**
         * @property defaultShader
         * @type AbstractFilter
         */
        this.defaultShader = new PIXI.AbstractFilter([
            'precision lowp float;',
            'varying vec2 vTextureCoord;',
            'varying vec4 vColor;',
            'uniform sampler2D uSampler;',
            'void main(void) {',
            '   gl_FragColor = texture2D(uSampler, vTextureCoord) * vColor ;',
            '}'
        ]);
    };

    /**
    * @method setContext
    * @param gl {WebGLContext} the current WebGL drawing context
    */
    PIXI.WebGLSpriteBatch.prototype.setContext = function(gl)
    {
        this.gl = gl;

        // create a couple of buffers
        this.vertexBuffer = gl.createBuffer();
        this.indexBuffer = gl.createBuffer();

        // 65535 is max index, so 65535 / 6 = 10922.

        //upload the index data
        gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, this.indexBuffer);
        gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, this.indices, gl.STATIC_DRAW);

        gl.bindBuffer(gl.ARRAY_BUFFER, this.vertexBuffer);
        gl.bufferData(gl.ARRAY_BUFFER, this.vertices, gl.DYNAMIC_DRAW);

        this.currentBlendMode = 99999;

        var shader = new PIXI.PixiShader(gl);

        shader.fragmentSrc = this.defaultShader.fragmentSrc;
        shader.uniforms = {};
        shader.init();

        this.defaultShader.shaders[gl.id] = shader;
    };

    /**
    * @method begin
    * @param renderSession {Object} The RenderSession object
    */
    PIXI.WebGLSpriteBatch.prototype.begin = function(renderSession)
    {
        this.renderSession = renderSession;
        this.shader = this.renderSession.shaderManager.defaultShader;

        this.start();
    };

    /**
    * @method end
    */
    PIXI.WebGLSpriteBatch.prototype.end = function()
    {
        this.flush();
    };

    /**
    * @method render
    * @param sprite {Sprite} the sprite to render when using this spritebatch
    * @param {Matrix} [matrix] - Optional matrix. If provided the Display Object will be rendered using this matrix, otherwise it will use its worldTransform.
    */
    PIXI.WebGLSpriteBatch.prototype.render = function(sprite, matrix)
    {
        var texture = sprite.texture;

        //  They provided an alternative rendering matrix, so use it
        var wt = sprite.worldTransform;

        if (matrix)
        {
            wt = matrix;
        }

        // check texture..
        if (this.currentBatchSize >= this.size)
        {
            this.flush();
            this.currentBaseTexture = texture.baseTexture;
        }

        // get the uvs for the texture
        var uvs = texture._uvs;

        // if the uvs have not updated then no point rendering just yet!
        if (!uvs)
        {
            return;
        }

        var aX = sprite.anchor.x;
        var aY = sprite.anchor.y;

        var w0, w1, h0, h1;

        if (texture.trim)
        {
            // if the sprite is trimmed then we need to add the extra space before transforming the sprite coords.
            var trim = texture.trim;

            w1 = trim.x - aX * trim.width;
            w0 = w1 + texture.crop.width;

            h1 = trim.y - aY * trim.height;
            h0 = h1 + texture.crop.height;
        }
        else
        {
            w0 = (texture.frame.width) * (1-aX);
            w1 = (texture.frame.width) * -aX;

            h0 = texture.frame.height * (1-aY);
            h1 = texture.frame.height * -aY;
        }

        var i = this.currentBatchSize * 4 * this.vertSize;
        var resolution = texture.baseTexture.resolution;

        var a = wt.a / resolution;
        var b = wt.b / resolution;
        var c = wt.c / resolution;
        var d = wt.d / resolution;
        var tx = wt.tx;
        var ty = wt.ty;

        var colors = this.colors;
        var positions = this.positions;

        if (this.renderSession.roundPixels)
        {
            // xy
            positions[i] = a * w1 + c * h1 + tx | 0;
            positions[i+1] = d * h1 + b * w1 + ty | 0;

            // xy
            positions[i+5] = a * w0 + c * h1 + tx | 0;
            positions[i+6] = d * h1 + b * w0 + ty | 0;

             // xy
            positions[i+10] = a * w0 + c * h0 + tx | 0;
            positions[i+11] = d * h0 + b * w0 + ty | 0;

            // xy
            positions[i+15] = a * w1 + c * h0 + tx | 0;
            positions[i+16] = d * h0 + b * w1 + ty | 0;
        }
        else
        {
            // xy
            positions[i] = a * w1 + c * h1 + tx;
            positions[i+1] = d * h1 + b * w1 + ty;

            // xy
            positions[i+5] = a * w0 + c * h1 + tx;
            positions[i+6] = d * h1 + b * w0 + ty;

             // xy
            positions[i+10] = a * w0 + c * h0 + tx;
            positions[i+11] = d * h0 + b * w0 + ty;

            // xy
            positions[i+15] = a * w1 + c * h0 + tx;
            positions[i+16] = d * h0 + b * w1 + ty;
        }

        // uv
        positions[i+2] = uvs.x0;
        positions[i+3] = uvs.y0;

        // uv
        positions[i+7] = uvs.x1;
        positions[i+8] = uvs.y1;

         // uv
        positions[i+12] = uvs.x2;
        positions[i+13] = uvs.y2;

        // uv
        positions[i+17] = uvs.x3;
        positions[i+18] = uvs.y3;

        // color and alpha
        var tint = sprite.tint;

        colors[i+4] = colors[i+9] = colors[i+14] = colors[i+19] = (tint >> 16) + (tint & 0xff00) + ((tint & 0xff) << 16) + (sprite.worldAlpha * 255 << 24);

        // increment the batchsize
        this.sprites[this.currentBatchSize++] = sprite;

    };

    /**
    * Renders a TilingSprite using the spriteBatch.
    *
    * @method renderTilingSprite
    * @param sprite {TilingSprite} the sprite to render
    */
    PIXI.WebGLSpriteBatch.prototype.renderTilingSprite = function(sprite)
    {
        var texture = sprite.tilingTexture;

        // check texture..
        if (this.currentBatchSize >= this.size)
        {
            this.flush();
            this.currentBaseTexture = texture.baseTexture;
        }

        // set the textures uvs temporarily
        if (!sprite._uvs)
        {
            sprite._uvs = new PIXI.TextureUvs();
        }

        var uvs = sprite._uvs;

        var w = texture.baseTexture.width;
        var h = texture.baseTexture.height;

        // var w = sprite._frame.sourceSizeW;
        // var h = sprite._frame.sourceSizeH;

        // w = 16;
        // h = 16;

        sprite.tilePosition.x %= w * sprite.tileScaleOffset.x;
        sprite.tilePosition.y %= h * sprite.tileScaleOffset.y;

        var offsetX = sprite.tilePosition.x / (w * sprite.tileScaleOffset.x);
        var offsetY = sprite.tilePosition.y / (h * sprite.tileScaleOffset.y);

        var scaleX = (sprite.width / w) / (sprite.tileScale.x * sprite.tileScaleOffset.x);
        var scaleY = (sprite.height / h) / (sprite.tileScale.y * sprite.tileScaleOffset.y);

        uvs.x0 = 0 - offsetX;
        uvs.y0 = 0 - offsetY;

        uvs.x1 = (1 * scaleX) - offsetX;
        uvs.y1 = 0 - offsetY;

        uvs.x2 = (1 * scaleX) - offsetX;
        uvs.y2 = (1 * scaleY) - offsetY;

        uvs.x3 = 0 - offsetX;
        uvs.y3 = (1 * scaleY) - offsetY;

        //  Get the sprites current alpha and tint and combine them into a single color
        var tint = sprite.tint;
        var color = (tint >> 16) + (tint & 0xff00) + ((tint & 0xff) << 16) + (sprite.worldAlpha * 255 << 24);

        var positions = this.positions;
        var colors = this.colors;

        var width = sprite.width;
        var height = sprite.height;

        // TODO trim??
        var aX = sprite.anchor.x;
        var aY = sprite.anchor.y;
        var w0 = width * (1-aX);
        var w1 = width * -aX;

        var h0 = height * (1-aY);
        var h1 = height * -aY;

        var i = this.currentBatchSize * 4 * this.vertSize;

        var resolution = texture.baseTexture.resolution;

        var wt = sprite.worldTransform;

        var a = wt.a / resolution;
        var b = wt.b / resolution;
        var c = wt.c / resolution;
        var d = wt.d / resolution;
        var tx = wt.tx;
        var ty = wt.ty;

        // xy
        positions[i++] = a * w1 + c * h1 + tx;
        positions[i++] = d * h1 + b * w1 + ty;
        // uv
        positions[i++] = uvs.x0;
        positions[i++] = uvs.y0;
        // color
        colors[i++] = color;

        // xy
        positions[i++] = (a * w0 + c * h1 + tx);
        positions[i++] = d * h1 + b * w0 + ty;
        // uv
        positions[i++] = uvs.x1;
        positions[i++] = uvs.y1;
        // color
        colors[i++] = color;

        // xy
        positions[i++] = a * w0 + c * h0 + tx;
        positions[i++] = d * h0 + b * w0 + ty;
        // uv
        positions[i++] = uvs.x2;
        positions[i++] = uvs.y2;
        // color
        colors[i++] = color;

        // xy
        positions[i++] = a * w1 + c * h0 + tx;
        positions[i++] = d * h0 + b * w1 + ty;
        // uv
        positions[i++] = uvs.x3;
        positions[i++] = uvs.y3;
        // color
        colors[i++] = color;

        // increment the batchsize
        this.sprites[this.currentBatchSize++] = sprite;
    };

    /**
    * Renders the content and empties the current batch.
    *
    * @method flush
    */
    PIXI.WebGLSpriteBatch.prototype.flush = function()
    {
        // If the batch is length 0 then return as there is nothing to draw
        if (this.currentBatchSize === 0)
        {
            return;
        }

        var gl = this.gl;
        var shader;

        if (this.dirty)
        {
            this.dirty = false;

            // bind the main texture
            gl.activeTexture(gl.TEXTURE0);

            // bind the buffers
            gl.bindBuffer(gl.ARRAY_BUFFER, this.vertexBuffer);
            gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, this.indexBuffer);

            shader = this.defaultShader.shaders[gl.id];

            // this is the same for each shader?
            var stride = this.vertSize * 4;
            gl.vertexAttribPointer(shader.aVertexPosition, 2, gl.FLOAT, false, stride, 0);
            gl.vertexAttribPointer(shader.aTextureCoord, 2, gl.FLOAT, false, stride, 2 * 4);

            // color attributes will be interpreted as unsigned bytes and normalized
            gl.vertexAttribPointer(shader.colorAttribute, 4, gl.UNSIGNED_BYTE, true, stride, 4 * 4);
        }

        // upload the verts to the buffer
        if (this.currentBatchSize > (this.size * 0.5))
        {
            gl.bufferSubData(gl.ARRAY_BUFFER, 0, this.vertices);
        }
        else
        {
            var view = this.positions.subarray(0, this.currentBatchSize * 4 * this.vertSize);
            gl.bufferSubData(gl.ARRAY_BUFFER, 0, view);
        }

        var nextTexture, nextBlendMode, nextShader;
        var batchSize = 0;
        var start = 0;

        var currentBaseTexture = null;
        var currentBlendMode = this.renderSession.blendModeManager.currentBlendMode;
        var currentShader = null;

        var blendSwap = false;
        var shaderSwap = false;
        var sprite;

        for (var i = 0, j = this.currentBatchSize; i < j; i++) {

            sprite = this.sprites[i];

            if (sprite.tilingTexture)
            {
                nextTexture = sprite.tilingTexture.baseTexture;
            }
            else
            {
                nextTexture = sprite.texture.baseTexture;
            }

            nextBlendMode = sprite.blendMode;
            nextShader = sprite.shader || this.defaultShader;

            blendSwap = currentBlendMode !== nextBlendMode;
            shaderSwap = currentShader !== nextShader; // should I use _UIDS???

            var skip = nextTexture.skipRender;

            if (skip && sprite.children.length > 0)
            {
                skip = false;
            }

            if ((currentBaseTexture !== nextTexture && !skip) || blendSwap || shaderSwap)
            {
                this.renderBatch(currentBaseTexture, batchSize, start);

                start = i;
                batchSize = 0;
                currentBaseTexture = nextTexture;

                if (blendSwap)
                {
                    currentBlendMode = nextBlendMode;
                    this.renderSession.blendModeManager.setBlendMode(currentBlendMode);
                }

                if (shaderSwap)
                {
                    currentShader = nextShader;

                    shader = currentShader.shaders[gl.id];

                    if (!shader)
                    {
                        shader = new PIXI.PixiShader(gl);

                        shader.fragmentSrc = currentShader.fragmentSrc;
                        shader.uniforms = currentShader.uniforms;
                        shader.init();

                        currentShader.shaders[gl.id] = shader;
                    }

                    // set shader function???
                    this.renderSession.shaderManager.setShader(shader);

                    if (shader.dirty)
                    {
                        shader.syncUniforms();
                    }

                    // both these only need to be set if they are changing..
                    // set the projection
                    var projection = this.renderSession.projection;
                    gl.uniform2f(shader.projectionVector, projection.x, projection.y);

                    // TODO - this is temporary!
                    var offsetVector = this.renderSession.offset;
                    gl.uniform2f(shader.offsetVector, offsetVector.x, offsetVector.y);

                    // set the pointers
                }
            }

            batchSize++;
        }

        this.renderBatch(currentBaseTexture, batchSize, start);

        // then reset the batch!
        this.currentBatchSize = 0;
    };

    /**
    * @method renderBatch
    * @param texture {Texture}
    * @param size {Number}
    * @param startIndex {Number}
    */
    PIXI.WebGLSpriteBatch.prototype.renderBatch = function(texture, size, startIndex)
    {
        if (size === 0)
        {
            return;
        }

        var gl = this.gl;

        // check if a texture is dirty..
        if (texture._dirty[gl.id])
        {
            if (!this.renderSession.renderer.updateTexture(texture))
            {
                //  If updateTexture returns false then we cannot render it, so bail out now
                return;
            }
        }
        else
        {
            // bind the current texture
            gl.bindTexture(gl.TEXTURE_2D, texture._glTextures[gl.id]);
        }

        // now draw those suckas!
        gl.drawElements(gl.TRIANGLES, size * 6, gl.UNSIGNED_SHORT, startIndex * 6 * 2);

        // increment the draw count
        this.renderSession.drawCount++;
    };

    /**
    * @method stop
    */
    PIXI.WebGLSpriteBatch.prototype.stop = function()
    {
        this.flush();
        this.dirty = true;
    };

    /**
    * @method start
    */
    PIXI.WebGLSpriteBatch.prototype.start = function()
    {
        this.dirty = true;
    };

    /**
    * Destroys the SpriteBatch.
    *
    * @method destroy
    */
    PIXI.WebGLSpriteBatch.prototype.destroy = function()
    {
        this.vertices = null;
        this.indices = null;

        this.gl.deleteBuffer(this.vertexBuffer);
        this.gl.deleteBuffer(this.indexBuffer);

        this.currentBaseTexture = null;

        this.gl = null;
    };