title: Read pixels from a WebGL texture
body: <p>I have a WebGLTexture object. How do I get pixels of that texture (similar to WebGL's readPixels, but for a texture)?</p>
  
  <p>One idea I have is to create a canvas and a WebGL context with preserveDrawingBuffer=true, and render my texture on this canvas so that it shows 2D flat, and then use readPixels. Is this approach reasonable? Does anyone have a sample code for this?</p>