content: package jp.co.cyberagent.android.gpuimage;
  
  import android.opengl.GLES20;
  
  public class GPUImageSobelThresholdFilter extends
  		GPUImage3x3TextureSamplingFilter {
      public static final String SOBEL_THRESHOLD_EDGE_DETECTION = "" +
      		"precision mediump float;\n" +
      		"\n" +
      		"varying vec2 textureCoordinate;\n" +
      		"varying vec2 leftTextureCoordinate;\n" +
      		"varying vec2 rightTextureCoordinate;\n" +
      		"\n" +
      		"varying vec2 topTextureCoordinate;\n" +
      		"varying vec2 topLeftTextureCoordinate;\n" +
      		"varying vec2 topRightTextureCoordinate;\n" +
      		"\n" +
      		"varying vec2 bottomTextureCoordinate;\n" +
      		"varying vec2 bottomLeftTextureCoordinate;\n" +
      		"varying vec2 bottomRightTextureCoordinate;\n" +
      		"\n" +
      		"uniform sampler2D inputImageTexture;\n" +
      		"uniform lowp float threshold;\n" +
      		"\n" +
      		"const highp vec3 W = vec3(0.2125, 0.7154, 0.0721);\n" +
      		"\n" +
      		"void main()\n" +
      		"{\n" +
      		"    float bottomLeftIntensity = texture2D(inputImageTexture, bottomLeftTextureCoordinate).r;\n" +
      		"    float topRightIntensity = texture2D(inputImageTexture, topRightTextureCoordinate).r;\n" +
      		"    float topLeftIntensity = texture2D(inputImageTexture, topLeftTextureCoordinate).r;\n" +
      		"    float bottomRightIntensity = texture2D(inputImageTexture, bottomRightTextureCoordinate).r;\n" +
      		"    float leftIntensity = texture2D(inputImageTexture, leftTextureCoordinate).r;\n" +
      		"    float rightIntensity = texture2D(inputImageTexture, rightTextureCoordinate).r;\n" +
      		"    float bottomIntensity = texture2D(inputImageTexture, bottomTextureCoordinate).r;\n" +
      		"    float topIntensity = texture2D(inputImageTexture, topTextureCoordinate).r;\n" +
      		"    float h = -topLeftIntensity - 2.0 * topIntensity - topRightIntensity + bottomLeftIntensity + 2.0 * bottomIntensity + bottomRightIntensity;\n" +
      		"    float v = -bottomLeftIntensity - 2.0 * leftIntensity - topLeftIntensity + bottomRightIntensity + 2.0 * rightIntensity + topRightIntensity;\n" +
      		"\n" +
      		"    float mag = 1.0 - length(vec2(h, v));\n" +
      		"    mag = step(threshold, mag);\n" +
      		"\n" +
      		"    gl_FragColor = vec4(vec3(mag), 1.0);\n" +
      		"}\n";
  
      private int mUniformThresholdLocation;
      private float mThreshold = 0.9f;
      
      public GPUImageSobelThresholdFilter() {
      	this(0.9f);
      }
      
      public GPUImageSobelThresholdFilter(float threshold) {
      	super(SOBEL_THRESHOLD_EDGE_DETECTION);
      	mThreshold = threshold;
      }
      
      @Override
      public void onInit() {
      	super.onInit();
      	mUniformThresholdLocation = GLES20.glGetUniformLocation(getProgram(), "threshold");
      }
      
      @Override
      public void onInitialized() {
      	super.onInitialized();
      	setThreshold(mThreshold);
      }
      
      public void setThreshold(final float threshold) {
      	mThreshold = threshold;
      	setFloat(mUniformThresholdLocation, threshold);
      }
  }
  