title: About the meaning of glInvalidateFramebuffer
body: <p>I have a question about the general use of glInvalidateFramebuffer:</p>
  
  <p>As far as I know, the purpose of glInvalidateFramebuffer is to "skip the store of framebuffer contents that are no longer needed". Its main purpose on tile based gpus is to get rid of depth and stencil contents if only color is needed after rendering. I do not understand why this is necessary. As far as I know if I render to an FBO then all of this data is stored in that FBO. Now if I do something with only the color contents or nothing with that FBO in a subsequent draw, why is the depth/stencil data accessed at all? It is supposedly stored somewhere and that eats bandwidth, but as far as I can tell it is already in FBOs GPU memory as the result of the render so when does that supposed expensive additional store operation happen?</p>
  
  <p>There are supposedly expensive preservaton steps for FBO attachments but why are those necessary if the data is already in Gpu memory as result of the render?</p>
  
  <p>Regards</p>