OpenGL-ES-滤镜-饱和度片元着色器

//纹理坐标

varying lowp vec2 varyingCoord;

//纹理

uniform sampler2D textureMap;

//饱和度

uniform lowp float saturation;

//色温过滤器

const lowp vec3  warmFilter = vec3(0.93,0.54,0);

//RGBtoYIQ

const mediump mat3 RGB2YIQ = mat3(0.299, 0.587, 0.114, 0.596, -0.274, -0.322, 0.212, -0.523, 0.311);

//YIQtoRGB

const mediump mat3 YIQ2RGB = mat3(1.0, 0.956, 0.621, 1.0, -0.272, -0.647, 1.0, -1.105, 1.702);

//亮度加权

const mediump vec3 lumanaceWeight = vec3(0.2125,0.7154,0.0721);

void main(){

    //读取每个像素点的颜色值

    lowp vec4 soource = texture2D(textureMap,varyingCoord);

    //dot(v1,v2) 向量点乘

    //亮度 = RGB值 * 亮度加权

    lowp float luminace = dot(soource.rgb,lumanaceWeight);

    //将亮度标量转换为vec3 向量

    lowp vec3 color = vec3(luminace,0,0);

    /*

     mix(x,y,a)：将颜色与颜色/纹理与纹理/纹理与颜色通过线性方程式混合

     方程式：x.(1-a)+y.a --> vec3向量颜色

     vec4(vec3,w);-->vec4向量

     */

    gl_FragColor  = vec4(mix(color,soource.rgb,saturation),soource.w);

}