GlSobelEdgeDetectionShader.java

package com.af.experiments.FxCameraApp.shaders;

public class GlSobelEdgeDetectionShader extends GlShaderGroup {

    protected String mShaderName = "edges";

    @Override
    public String getName() {
        return mShaderName;
    }

    private static final String FRAGMENT_SHADER =
            "precision mediump float;\n" +

                    "uniform lowp sampler2D sTexture;\n" +

                    "varying vec2 textureCoordinate;\n" +
                    "varying vec2 leftTextureCoordinate;\n" +
                    "varying vec2 rightTextureCoordinate;\n" +

                    "varying vec2 topTextureCoordinate;\n" +
                    "varying vec2 topLeftTextureCoordinate;\n" +
                    "varying vec2 topRightTextureCoordinate;\n" +

                    "varying vec2 bottomTextureCoordinate;\n" +
                    "varying vec2 bottomLeftTextureCoordinate;\n" +
                    "varying vec2 bottomRightTextureCoordinate;\n" +

                    "void main() {\n" +
                    "float bottomLeftIntensity = texture2D(sTexture, bottomLeftTextureCoordinate).r;" +
                    "float topRightIntensity = texture2D(sTexture, topRightTextureCoordinate).r;" +
                    "float topLeftIntensity = texture2D(sTexture, topLeftTextureCoordinate).r;" +
                    "float bottomRightIntensity = texture2D(sTexture, bottomRightTextureCoordinate).r;" +
                    "float leftIntensity = texture2D(sTexture, leftTextureCoordinate).r;" +
                    "float rightIntensity = texture2D(sTexture, rightTextureCoordinate).r;" +
                    "float bottomIntensity = texture2D(sTexture, bottomTextureCoordinate).r;" +
                    "float topIntensity = texture2D(sTexture, topTextureCoordinate).r;" +

                    "float h = -topLeftIntensity - 2.0 * topIntensity - topRightIntensity + bottomLeftIntensity + 2.0 * bottomIntensity + bottomRightIntensity;" +
                    "float v = -bottomLeftIntensity - 2.0 * leftIntensity - topLeftIntensity + bottomRightIntensity + 2.0 * rightIntensity + topRightIntensity;" +

                    "float mag = length(vec2(h, v));" +
                    "gl_FragColor = vec4(vec3(mag), 1.0);" +
                    "}";

    public GlSobelEdgeDetectionShader() {
        this(FRAGMENT_SHADER);
    }

    protected GlSobelEdgeDetectionShader(final String fragmentShaderSource) {
        super(new GlGrayScaleShader(), new GlThreex3TextureSamplingShader(fragmentShaderSource));
    }

}