GPUImageHistogramGenerator.m
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#import "GPUImageHistogramGenerator.h"
NSString *const kGPUImageHistogramGeneratorVertexShaderString = SHADER_STRING
(
attribute vec4 position;
attribute vec4 inputTextureCoordinate;
varying vec2 textureCoordinate;
varying float height;
void main()
{
gl_Position = position;
textureCoordinate = vec2(inputTextureCoordinate.x, 0.5);
height = 1.0 - inputTextureCoordinate.y;
}
);
#if TARGET_IPHONE_SIMULATOR || TARGET_OS_IPHONE
NSString *const kGPUImageHistogramGeneratorFragmentShaderString = SHADER_STRING
(
varying highp vec2 textureCoordinate;
varying highp float height;
uniform sampler2D inputImageTexture;
uniform lowp vec4 backgroundColor;
void main()
{
lowp vec3 colorChannels = texture2D(inputImageTexture, textureCoordinate).rgb;
lowp vec4 heightTest = vec4(step(height, colorChannels), 1.0);
gl_FragColor = mix(backgroundColor, heightTest, heightTest.r + heightTest.g + heightTest.b);
}
);
#else
NSString *const kGPUImageHistogramGeneratorFragmentShaderString = SHADER_STRING
(
varying vec2 textureCoordinate;
varying float height;
uniform sampler2D inputImageTexture;
uniform vec4 backgroundColor;
void main()
{
vec3 colorChannels = texture2D(inputImageTexture, textureCoordinate).rgb;
vec4 heightTest = vec4(step(height, colorChannels), 1.0);
gl_FragColor = mix(backgroundColor, heightTest, heightTest.r + heightTest.g + heightTest.b);
}
);
#endif
@implementation GPUImageHistogramGenerator
#pragma mark -
#pragma mark Initialization and teardown
- (id)init;
{
if (!(self = [super initWithVertexShaderFromString:kGPUImageHistogramGeneratorVertexShaderString fragmentShaderFromString:kGPUImageHistogramGeneratorFragmentShaderString]))
{
return nil;
}
backgroundColorUniform = [filterProgram uniformIndex:@"backgroundColor"];
[self setBackgroundColorRed:0.0 green:0.0 blue:0.0 alpha:0.0];
return self;
}
#pragma mark -
#pragma mark Accessors
- (void)setBackgroundColorRed:(GLfloat)redComponent green:(GLfloat)greenComponent blue:(GLfloat)blueComponent alpha:(GLfloat)alphaComponent;
{
// GLfloat backgroundColor[4];
// backgroundColor[0] = redComponent;
// backgroundColor[1] = greenComponent;
// backgroundColor[2] = blueComponent;
// backgroundColor[3] = alphaComponent;
GPUVector4 backgroundColor = {redComponent, greenComponent, blueComponent, alphaComponent};
[self setVec4:backgroundColor forUniform:backgroundColorUniform program:filterProgram];
}
@end