text: 
  #if __has_include(<GPUImage/GPUImageFramework.h>)
  #import <GPUImage/GPUImageFilter.h>
  #else
  #import "GPUImageFilter.h"
  #endif
  
  extern NSString *const kGPUImageNearbyTexelSamplingVertexShaderString;
  
  @interface GPUImage3x3TextureSamplingFilter : GPUImageFilter
  {
      GLint texelWidthUniform, texelHeightUniform;
      
      CGFloat texelWidth, texelHeight;
      BOOL hasOverriddenImageSizeFactor;
  }
  
  // The texel width and height determines how far out to sample from this texel. By default, this is the normalized width of a pixel, but this can be overridden for different effects.
  @property(readwrite, nonatomic) CGFloat texelWidth; 
  @property(readwrite, nonatomic) CGFloat texelHeight; 
  
  
  @end
  