@Override
    public void onDraw() {
        GLES20.glUniform1f(getHandle("contrast"), contrast);
    }
Changes the contrast of the image.
contrast value ranges from 0.0 to 4.0, with 1.0 as the normal level
dkplayer-sample/src/main/java/xyz/doikki/dkplayer/widget/render/gl2/filter/GlContrastFilter.java