urrent time for the next frame.
    then = time;

    // Animate the rotation
    modelYRotationRadians += -0.7 * deltaTime;
    modelXRotationRadians += -0.4 * deltaTime;

    webglUtils.resizeCanvasToDisplaySize(gl.canvas);

    gl.enable(gl.CULL_FACE);
    gl.enable(gl.DEPTH_TEST);

    {
      // render to our targetTexture by binding the framebuffer
      gl.bindFramebuffer(gl.FRAMEBUFFER, fb);

      // render cube with our 3x2 texture
      gl.bindTexture(gl.TEXTURE_2D, texture);

      // Tell WebGL