title: pass data between shader programs
body: <p>Ok I'm going to keep this as simple as possible.  I want to pass data between shader programs. I'm using readPixels currently to do that but I feel it may be slowing operations down and I'm exploring faster options.</p>
  
  <p>what my program does:</p>
  
  <ol>
  <li>program1 does my rendering to the canvas.</li>
  <li>program2 does some wonderful operations in it's shaders that I want to pass to program1.</li>
  </ol>
  
  <p>MY QUESTIONS:</p>
  
  <ol>
  <li><strong>is it possible to use the vbo from program2 and pass that to program1 for rendering? From what it sounds like in the link I give below, you can't share data across contexts, meaning the data from one buffer can't be used for another. But maybe I'm missing something.</strong></li>
  <li><strong>I believe the method mentioned in this article would do what I'm looking for by rendering to a canvas and then using texImage2D to update program1 (<a href="https://stackoverflow.com/questions/56063666/copy-framebuffer-data-from-one-webglrenderingcontext-to-another">Copy framebuffer data from one WebGLRenderingContext to another?</a>).  Am I correct? If so, would this be faster than using readPixels?</strong> ( i ask because if using texImage2D is about the same I won't bother ).</li>
  </ol>
  
  <p>thanks in advance to anyone who answers.</p>