GPUImage – 色阶 GPUImageLevelsFilter

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//@Author:猿说编程
//@Blog(个人博客地址): www.codersrc.com
//@File:GPUImage – 色阶 GPUImageLevelsFilter
//@Time:2022/03/28 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 kGPUImageLevelsFragmentShaderString = SHADER_STRING
(
 varying highp vec2 textureCoordinate;

 uniform sampler2D inputImageTexture;
 uniform mediump vec3 levelMinimum;
 uniform mediump vec3 levelMiddle;
 uniform mediump vec3 levelMaximum;
 uniform mediump vec3 minOutput;
 uniform mediump vec3 maxOutput;

 void main()
 {
     mediump vec4 textureColor = texture2D(inputImageTexture, textureCoordinate);

     gl_FragColor = vec4(LevelsControl(textureColor.rgb, levelMinimum, levelMiddle, levelMaximum, minOutput, maxOutput), textureColor.a);
 }
);
#else
NSString *const kGPUImageLevelsFragmentShaderString = SHADER_STRING
(
 varying vec2 textureCoordinate;

 uniform sampler2D inputImageTexture;
 uniform vec3 levelMinimum;
 uniform vec3 levelMiddle;
 uniform vec3 levelMaximum;
 uniform vec3 minOutput;
 uniform vec3 maxOutput;

 void main()
 {
     vec4 textureColor = texture2D(inputImageTexture, textureCoordinate);

     gl_FragColor = vec4(LevelsControl(textureColor.rgb, levelMinimum, levelMiddle, levelMaximum, minOutput, maxOutput), textureColor.a);
 }
);
#endif