OpenGL-ES-滤镜-色温片元着色器

//纹理坐标

varying lowp vec2 varyingCoord;

//纹理

uniform sampler2D textureMap;

//色温

uniform lowp float temperature;

//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 source = texture2D(textureMap,textureCoordinate);

//源颜色RGB转换为YIQ颜色

mediump vec3 yiq = RGB2YIQ * source.rgb;

clamp(x,minVal,maxVal):裁剪

1.x与minVal比较，取较大值；

2.上一步得到的结果与maxVal比较，取较小值；

yiq.b：b ->指yiq中的第三个值，而不是其b值

yiq.b = clamp(yiq.b,-0.5226,0.5226);

//YIQ颜色转RGB颜色

lowp vec3 rgb = YIQ2RGB * yiq;

色温计算:

warmR:色温h过滤器--warmFilter

if r<0.5 -->2.0*r*warmR;

if r>= 0.5-->1.0-2.0*(1.0-r)*(1.0-warmR);

lowp float A = (rgb.r <0.5? (2.0* rgb.r * warmFilter.r) : (1.0-2.0* (1.0- rgb.r) * (1.0- warmFilter.r)));

lowp float B = (rgb.g <0.5? (2.0* rgb.g * warmFilter.g) : (1.0-2.0* (1.0- rgb.g) * (1.0- warmFilter.g)));

lowp float C = (rgb.b <0.5? (2.0* rgb.b * warmFilter.b) : (1.0-2.0* (1.0- rgb.b) * (1.0- warmFilter.b)));

//组件新的颜色值

lowp vec3 color =vec3(A,B,C);

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(rgb,color，temperature),source.a);

}