In my Metal app for macOS, I have a situation where I only want to display the render results every so often. I want to complete the rendering pass every frame, and save the drawable texture image to a file, but I only want to display the render every sixteenth frame or so. I tried just skipping commandBuffer.present(drawable) when I don't want to display, but it is not working. It just stops displaying new frames once I do that. After skipping one call to commandBuffer.present(), it just doesn't display any new frames. It does continue to run, however.
Why would that happen? Once I commit a command buffer, is it required for it to be presented?
If I can't get this to work, then I will try to render into an offscreen buffer for these frames I don't want displayed. But it would be extra work and require more memory for the offscreen render buffer, so I'd rather just be able to use my regular onscreen render buffer if possible.
Thanks!
It's not required that a command buffer present a drawable. I think the issue is that, once you've obtained the drawable, it's not returned to the pool maintained by the CAMetalLayer (or, indirectly, MTKView) that provided it until it is presented.
Do not render to a drawable's texture if you don't plan on presenting. Rendering to an off-screen texture is the right approach. In fact, if you always render first to an off-screen texture and then, only for the frames you want to display, copy that to a drawable's texture, then you can leave the framebufferOnly property of the CAMetalLayer with its default true value. In that case, there's a decent chance that you won't increase the memory required (because the drawable's texture is really just part of the screen's backing store).