IOS – OPenGL ES 调节图像饱和度 GPUImageSaturationFilter

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//@Author:猿说编程
//@Blog(个人博客地址): www.codersrc.com
//@File:IOS – OPenGL ES 调节图像饱和度 GPUImageSaturationFilter
//@Time:2022/03/12 07:30
//@Motto:不积跬步无以至千里，不积小流无以成江海，程序人生的精彩需要坚持不懈地积累！
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#if TARGET_IPHONE_SIMULATOR || TARGET_OS_IPHONE
NSString *const kGPUImageSaturationFragmentShaderString = SHADER_STRING
(
 varying highp vec2 textureCoordinate;

 uniform sampler2D inputImageTexture;
 uniform lowp float saturation;

 // Values from "Graphics Shaders: Theory and Practice" by Bailey and Cunningham
 const mediump vec3 luminanceWeighting = vec3(0.2125, 0.7154, 0.0721);

 void main()
 {
    lowp vec4 textureColor = texture2D(inputImageTexture, textureCoordinate);
    lowp float luminance = dot(textureColor.rgb, luminanceWeighting);
    lowp vec3 greyScaleColor = vec3(luminance);

    gl_FragColor = vec4(mix(greyScaleColor, textureColor.rgb, saturation), textureColor.w);

 }
);
#else
NSString *const kGPUImageSaturationFragmentShaderString = SHADER_STRING
(
 varying vec2 textureCoordinate;

 uniform sampler2D inputImageTexture;
 uniform float saturation;

 // Values from "Graphics Shaders: Theory and Practice" by Bailey and Cunningham
 const vec3 luminanceWeighting = vec3(0.2125, 0.7154, 0.0721);

 void main()
 {
     vec4 textureColor = texture2D(inputImageTexture, textureCoordinate);
     float luminance = dot(textureColor.rgb, luminanceWeighting);
     vec3 greyScaleColor = vec3(luminance);

     gl_FragColor = vec4(mix(greyScaleColor, textureColor.rgb, saturation), textureColor.w);

 }
 );
#endif