Cocos2dx 使用Shader使精灵变灰

使用方法：

auto spr = Sprite::create("spr.png");
auto program = CCGLProgram::createWithFilenames("gray.vsh", "gray.fsh"); //装配一个shader文件
program->link();
program->updateUniforms();

spr->setShaderProgram(program);

this->addChild(spr);

gray.vsh:

attribute vec4 a_position;  //内置的默认坐标
attribute vec2 a_texCoord;  //内置的默认纹理坐标
attribute vec4 a_color;     //内置的默认颜色


varying vec4 v_fragmentColor;
varying vec2 v_texCoord;

void main()
{
    gl_Position = CC_PMatrix * a_position;
    v_fragmentColor = a_color;
    v_texCoord = a_texCoord;
}

gray.fsh:

varying vec4 v_fragmentColor;
varying vec2 v_texCoord;

void main(void)
{
     vec4 c = texture2D(CC_Texture0, v_texCoord);
     gl_FragColor.xyz = vec3(0.2126*c.r + 0.7152*c.g + 0.0722*c.b);
     gl_FragColor.w = c.w;
}

原理比较简单，gl_FragColor是shader的内建变量，表示当前片段的颜色，代码中是把从采样器中（CC_Texture0）拿到的颜色值进行一个变灰处理后，最后得到的颜色值再赋值给gl_FragColor