cocos2d-js Shader系列3：多重纹理 multiple textures multiple samplers

浏览数：168 / 时间：2015年06月09日

上一篇，我们学习了怎么便捷的控制sprite的颜色，而这个都是默认一个texture的，如果要实现类似mask的效果，或者更个性化的多纹理效果，怎么实现呢？

这就是这一节需要介绍的内容。

例如上图的效果，下方2个球是原图，而上方的图就是由2个球通过某个公式合成的效果了。这里重点不是怎么合成，而是怎么把多个纹理推送到fragment shader中。

相信大家都会想到，首先需要在fragment shader中添加多一个Sample2D：

uniform sampler2D CC_Texture0
uniform sampler2D CC_Texture1

但是通过简单的绑定纹理，只能绑定到第一个sampler上：

this.tex1 = cc.textureCache.addImage("res2/item_2.png");
gl.bindTexture(gl.TEXTURE_2D, this.tex1)

那么关键点来了，我们需要利用gl的32个texture缓存。
this.tex1Location = gl.getUniformLocation(p, "CC_Texture0");     
this.tex2Location = gl.getUniformLocation(p, "CC_Texture1");

gl.activeTexture(gl.TEXTURE0);          //webgl中一共32个，可以看cocos2d列的常量 
gl.bindTexture(gl.TEXTURE_2D, this.tex1.getName()); 
gl.uniform1i(this.tex1Location, 0);     //把CC_Texture0指向gl.TEXTURE0 
gl.activeTexture(gl.TEXTURE1); 
gl.bindTexture(gl.TEXTURE_2D, this.tex2.getName()); 
gl.uniform1i(this.tex1Location, 1);
核心是先激活某个纹理缓存，然后绑定sampler2D到对应的位置。最后，我们需要记得在draw之后清空，否则会影响下一个Node的绘制。

gl.activeTexture(gl.TEXTURE0); 
gl.bindTexture(gl.TEXTURE_2D, null); 
gl.activeTexture(gl.TEXTURE1); 
gl.bindTexture(gl.TEXTURE_2D, null);         
gl.bindBuffer(gl.ARRAY_BUFFER, null);

全部代码：

var MultiTexturesLayer = cc.Layer.extend({ 
    ctor:function() { 
        this._super(); 
        if( ‘opengl‘ in cc.sys.capabilities ) { 
            var node1 = new cc.Sprite("res2/item_2.png"); 
            var node2 = new cc.Sprite("res2/item_3.png"); 
            this.addChild(node1); 
            this.addChild(node2); 
            node1.x = 500; 
            node2.x = 200; 
            node1.y = node2.y = 400; 
            var glnode = new cc.Node(); 
            this.addChild(glnode,10); 
            this.glnode = glnode; 
            var winSize = cc.director.getWinSize(); 
            glnode.x = winSize.width/2; 
            glnode.y = winSize.height/2; 
            glnode.width = 128; 
            glnode.height = 128; 
            glnode.anchorX = 0.5; 
            glnode.anchorY = 0.5; 
            var MULTI_TEXTURES_FRAGMENT_SHADER = 
                "precision lowp float;   \n" 
                + "varying vec2 v_texCoord;  \n" 
                + "uniform sampler2D CC_Texture0; \n" 
                + "uniform sampler2D CC_Texture1; \n" 
                + "void main() \n" 
                + "{  \n" 
                    + "    vec4 color1 =  texture2D(CC_Texture0, v_texCoord);   \n" 
                    + "    vec4 color2 =  texture2D(CC_Texture1, v_texCoord);   \n" 
                    + "    gl_FragColor = vec4(color1.r*color2.r, color1.g*color2.g, color1.b*color2.b, color1.a*color2.a);   \n" 
                + "}"; 
            var DEFAULT_VERTEX_SHADER = 
                "attribute vec4 a_position; \n" 
                + "attribute vec2 a_texCoord; \n" 
                + "varying mediump vec2 v_texCoord; \n" 
                + "void main() \n" 
                + "{ \n" 
                + "    gl_Position = (CC_PMatrix * CC_MVMatrix) * a_position;  \n" 
                + "    v_texCoord = a_texCoord;               \n" 
                + "}"; 
            this.shader = new cc.GLProgram(); 
            this.shader.initWithVertexShaderByteArray(DEFAULT_VERTEX_SHADER, MULTI_TEXTURES_FRAGMENT_SHADER); 
            this.shader.addAttribute(cc.ATTRIBUTE_NAME_POSITION, cc.VERTEX_ATTRIB_POSITION); 
            this.shader.addAttribute(cc.ATTRIBUTE_NAME_TEX_COORD, cc.VERTEX_ATTRIB_TEX_COORDS); 
            this.shader.link(); 
            this.shader.updateUniforms();   //绑定位置，这个是cocos封装后必须做的事。详细可以看代码 
            this.initGL(); 
            var p = this.shader.getProgram(); 
            this.tex1Location = gl.getUniformLocation(p, "CC_Texture0");    //如果frag shader最终没有用某个uniform，该uniform会被优化删掉 
            this.tex2Location = gl.getUniformLocation(p, "CC_Texture1"); 
            trace(this.tex1Location, this.tex2Location); 
            glnode.draw = function() { 
                this.shader.use();                      //使用这个shader来绘制，封装了gl的use。跟指定glnode.shaderProgram类似 
                this.shader.setUniformsForBuiltins();   //设置坐标系变换 
                gl.activeTexture(gl.TEXTURE0);          //webgl中一共32个，可以看cocos2d列的常量 
                gl.bindTexture(gl.TEXTURE_2D, this.tex1.getName()); 
                gl.uniform1i(this.tex1Location, 0);     //把CC_Texture0指向gl.TEXTURE0 
                gl.activeTexture(gl.TEXTURE1); 
                gl.bindTexture(gl.TEXTURE_2D, this.tex2.getName()); 
                gl.uniform1i(this.tex1Location, 1); 
                cc.glEnableVertexAttribs( cc.VERTEX_ATTRIB_FLAG_TEX_COORDS | cc.VERTEX_ATTRIB_FLAG_POSITION);   //实际对gl的api做了封装，增加了这两个属性的位置映射。用于vertexAttribPointer 
                // Draw fullscreen Square 
                gl.bindBuffer(gl.ARRAY_BUFFER, this.squareVertexPositionBuffer); 
                gl.vertexAttribPointer(cc.VERTEX_ATTRIB_POSITION, 2, gl.FLOAT, false, 0, 0); 
                gl.bindBuffer(gl.ARRAY_BUFFER, this.squareVertexTextureBuffer); 
                gl.vertexAttribPointer(cc.VERTEX_ATTRIB_TEX_COORDS, 2, gl.FLOAT, false, 0, 0); 
                gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4); 
                gl.activeTexture(gl.TEXTURE0); 
                gl.bindTexture(gl.TEXTURE_2D, null); 
                gl.activeTexture(gl.TEXTURE1); 
                gl.bindTexture(gl.TEXTURE_2D, null);        //使用完必须置为空，否则影响其他node 
                gl.bindBuffer(gl.ARRAY_BUFFER, null); 
            }.bind(this); 
        } 
    }, 
    initGL:function() { 
        var tex1 = cc.textureCache.addImage("res2/item_2.png"); 
        var tex2 = cc.textureCache.addImage("res2/item_3.png"); 
        this.tex1 = tex1; 
        this.tex2 = tex2; 
        // 
        // Square 
        // 
        var squareVertexPositionBuffer = this.squareVertexPositionBuffer = gl.createBuffer(); 
        gl.bindBuffer(gl.ARRAY_BUFFER, squareVertexPositionBuffer); 
        var vertices = [ 
            128,  128, 
            0,    128, 
            128,  0, 
            0,    0 
        ]; 
        gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW); 
        var squareVertexTextureBuffer = this.squareVertexTextureBuffer = gl.createBuffer(); 
        gl.bindBuffer(gl.ARRAY_BUFFER, squareVertexTextureBuffer); 
        var texcoords = [ 
            0, 0, 
            1, 0, 
            0, 1, 
            1, 1 
        ]; 
        gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(texcoords), gl.STATIC_DRAW); 
        gl.bindBuffer(gl.ARRAY_BUFFER, null); 
    } 
});