glsl计算sprite的亮度饱和度对比度

//glsl计算sprite的亮度饱和度对比度
#ifdef GL_ES
precision mediump float;
#endif
uniform sampler2D u_texture;
varying vec2 v_texCoord;
varying vec4 v_fragmentColor;               

void main(void)
{
    vec4 color = texture2D(u_texture, v_texCoord);
    if(color.a >= 0.4)
    {
        vec3 avg = vec3(0.5,0.5,0.5);
        vec3 luncoeff = vec3 (0.2125, 0.7154, 0.0721);
        float T1 = 0.4;
        float T2 = 2.4;
        //计算亮度
        vec3 brtColor = color.rgb * T2;
        float intensityf = dot(brtColor,luncoeff);
        vec3 intensity = vec3(intensityf,intensityf,intensityf);
        //计算饱和度
        vec3 satColor = vec3(mix(intensity, brtColor, .));
        //计算对比度
        vec3 conColor = vec3(mix(avg, satColor, T1));
        gl_FragColor = vec4(conColor.r,conColor.g,conColor.b,color.a);
    }
    else
    {
        gl_FragColor = color;
    }
}