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| #import "GPUImageFilter.h" | ||
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| @interface GPUImageHueFilter : GPUImageFilter | ||
| { | ||
| GLfloat hueAdjustUniform; | ||
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| } | ||
| @property (nonatomic, readwrite) CGFloat hue; | ||
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| @end |
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| #import "GPUImageHueFilter.h" | ||
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| // Adapted from http://stackoverflow.com/questions/9234724/how-to-change-hue-of-a-texture-with-glsl - see for code and discussion | ||
| NSString *const kGPUImageHueFragmentShaderString = SHADER_STRING | ||
| ( | ||
| precision highp float; | ||
| varying highp vec2 textureCoordinate; | ||
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| uniform sampler2D inputImageTexture; | ||
| uniform mediump float hueAdjust; | ||
| const highp vec4 kRGBToYPrime = vec4 (0.299, 0.587, 0.114, 0.0); | ||
| const highp vec4 kRGBToI = vec4 (0.595716, -0.274453, -0.321263, 0.0); | ||
| const highp vec4 kRGBToQ = vec4 (0.211456, -0.522591, 0.31135, 0.0); | ||
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| const highp vec4 kYIQToR = vec4 (1.0, 0.9563, 0.6210, 0.0); | ||
| const highp vec4 kYIQToG = vec4 (1.0, -0.2721, -0.6474, 0.0); | ||
| const highp vec4 kYIQToB = vec4 (1.0, -1.1070, 1.7046, 0.0); | ||
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| void main () | ||
| { | ||
| // Sample the input pixel | ||
| highp vec4 color = texture2D(inputImageTexture, textureCoordinate); | ||
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| // Convert to YIQ | ||
| highp float YPrime = dot (color, kRGBToYPrime); | ||
| highp float I = dot (color, kRGBToI); | ||
| highp float Q = dot (color, kRGBToQ); | ||
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| // Calculate the hue and chroma | ||
| highp float hue = atan (Q, I); | ||
| highp float chroma = sqrt (I * I + Q * Q); | ||
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| // Make the user's adjustments | ||
| hue += (-hueAdjust); //why negative rotation? | ||
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| // Convert back to YIQ | ||
| Q = chroma * sin (hue); | ||
| I = chroma * cos (hue); | ||
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| // Convert back to RGB | ||
| highp vec4 yIQ = vec4 (YPrime, I, Q, 0.0); | ||
| color.r = dot (yIQ, kYIQToR); | ||
| color.g = dot (yIQ, kYIQToG); | ||
| color.b = dot (yIQ, kYIQToB); | ||
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| // Save the result | ||
| gl_FragColor = color; | ||
| } | ||
| ); | ||
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| @implementation GPUImageHueFilter | ||
| @synthesize hue; | ||
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| -(id) init { | ||
| if(! (self = [super initWithFragmentShaderFromString:kGPUImageHueFragmentShaderString]) ){ | ||
| return nil; | ||
| } | ||
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| hueAdjustUniform = [filterProgram uniformIndex:@"hueAdjust"]; | ||
| self.hue = 90; | ||
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| return self; | ||
| } | ||
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| -(void) setHue:(CGFloat)newHue { | ||
| hue = fmodf(newHue, 360.0); | ||
| [GPUImageOpenGLESContext useImageProcessingContext]; | ||
| [filterProgram use]; | ||
| glUniform1f(hueAdjustUniform, hue); | ||
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| } | ||
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| @end |