uniform sampler2D displacementMap;
uniform highp float displacementSize;
uniform highp vec4 displacementUV;

varying highp vec2 displacementUVOut;

void vertex() {
    displacementUVOut = mix(displacementUV.xy, displacementUV.zw, tCoord2);
}

void fragment() {
    highp vec4 displacementSample = texture2D(displacementMap, displacementUVOut);
    highp vec2 displacementValue = (displacementSample.xy - vec2(128.0 / 255.0)) / (1.0 - 128.0 / 255.0);
    COLOR = zTexture(UV + displacementValue * TEXTURE_PIXEL_SIZE * displacementSize * vec2(1.0, -1.0));
    COLOR.a *= displacementSample.a;
}