public class ShaderBatch extends SpriteBatch {

    static final String vertexShader = "attribute vec4 " + ShaderProgram.POSITION_ATTRIBUTE + ";\n" //
        + "attribute vec4 " + ShaderProgram.COLOR_ATTRIBUTE + ";\n" //
        + "attribute vec2 " + ShaderProgram.TEXCOORD_ATTRIBUTE + "0;\n" //
        + "uniform mat4 u_projTrans;\n" //
        + "varying vec4 v_color;\n" //
        + "varying vec2 v_texCoords;\n" //
        + "\n" //
        + "void main()\n" //
        + "{\n" //
        + "   v_color = " + ShaderProgram.COLOR_ATTRIBUTE + ";\n" //
        + "   v_texCoords = " + ShaderProgram.TEXCOORD_ATTRIBUTE + "0;\n" //
        + "   gl_Position =  u_projTrans * " + ShaderProgram.POSITION_ATTRIBUTE + ";\n" //
        + "}\n";

    static final String fragmentShader = "#ifdef GL_ES\n" //
        + "#define LOWP lowp\n" //
        + "precision mediump float;\n" //
        + "#else\n" //
        + "#define LOWP \n" //
        + "#endif\n" //
        + "varying LOWP vec4 v_color;\n" //
        + "varying vec2 v_texCoords;\n" //
        + "uniform sampler2D u_texture;\n" //
        + "uniform float brightness;\n" //
        + "uniform float contrast;\n" //
        + "void main()\n"//
        + "{\n" //
        + "  vec4 color = v_color * texture2D(u_texture, v_texCoords);\n"
        + "  color.rgb /= color.a;\n" //ignore alpha
        + "  color.rgb = ((color.rgb - 0.5) * max(contrast, 0.0)) + 0.5;\n" //apply contrast
        + "  color.rgb += brightness;\n" //apply brightness
        + "  color.rgb *= color.a;\n" //return alpha
        + "  gl_FragColor = color;\n"
        + "}";

    ShaderProgram shader;
    public final boolean isCompiled;
    public final String log;

    protected int brightnessLoc=-1, contrastLoc=-1;

    //ideally use getters/setters here...
    public float brightness=0f;
    public float contrast=1f;

    public ShaderBatch(int size) {
        super(size);

        if (Gdx.graphics.isGL20Available()) {
            ShaderProgram.pedantic = false;
            shader = new ShaderProgram(vertexShader, fragmentShader);
            isCompiled = shader.isCompiled();
            log = shader.getLog();
            if (isCompiled) {
                setShader(shader);
                begin();
                brightnessLoc = shader.getUniformLocation("brightness");
                contrastLoc = shader.getUniformLocation("contrast");
                end();
            }
        } else {
            isCompiled = false;
            log = "Shaders not supported in GL11";
        }
    }

    public void begin() {
        super.begin();
        if (brightnessLoc!=-1 && shader!=null)
            shader.setUniformf(brightnessLoc, brightness);
        if (contrastLoc!=-1 && shader!=null)
            shader.setUniformf(contrastLoc, contrast);
    }
}