R"#(
precision highp float;
varying vec2 v_texcoord; // is in 0-1
uniform sampler2D tex;
uniform sampler2D texMatte;

void main() {
    gl_FragColor = texture2D(tex, v_texcoord) * texture2D(texMatte, v_texcoord)[0]; // I know it only uses R, but matte should be black/white anyways.
}
)#"
