        varying vec2 texCoord;
        void main() {
            gl_Position = vec4(vPosition.xy, 0.0, 1.0);
            texCoord = vPosition.xy * 2.0;
        }`;
    const program = wtu.setupProgram(gl, [vs, wtu.simpleTextureFragmentShader]);
    gl.useProgram(program);

    const black = [  0,   0,   0, 255];
    const red   = [255,   0,   0, 255];
    const green = [  0, 255,   0, 255];
    const blue  = [  0,   0, 255, 255];
    const data = new Uint8Array([...black, ...red, ...green, ...blue]);

    f