r2D u_tex0;
void main() {
    gl_FragColor = texture2D(u_tex0, vec2(0));
}
`;

const prog = wtu.loadProgram(gl, VS, FS);
gl.useProgram(prog);

(() => {
    const MIPS = 3;
    const SIZE = 10;

    const immutTex = gl.createTexture();
    immutTex.name = "immutTex";
    immutTex.immutable = true;
    gl.bindTexture(gl.TEXTURE_2D, immutTex);
    gl.texStorage2D(gl.TEXTURE_2D, MIPS, gl.RGBA8, SIZE, SIZE);

    const mutTex = gl.createTexture();
    mutTex.name = "mutTex";
    mutTex.immutable = false;
    gl.