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[MANTA] Re: Asynchronous i/o in manta and conventional gui's


Chronological Thread 
  • From: Abe Stephens <abe@sci.utah.edu>
  • To: "'manta@sci.utah.edu'" <manta@sci.utah.edu>
  • Subject: [MANTA] Re: Asynchronous i/o in manta and conventional gui's
  • Date: Mon, 13 Jun 2005 15:36:43 -0700
[This thread started on a subset of the manta list, but it might be interesting to a wider audience.]

Maybe my disconnect here is that manta really has its own control loop which is separate from the gui toolkit's. The question is, how does the gui toolkit (or whatever is reading the frames) know how often to load a new frame from where ever the renderer leaves it?

It seems like what we really want is for the readiness of a new image to be treated as a message event type inside of the gui framework, just as a keystroke would be. I doubt this functionality is available inside glut, does anyone know if it is available in other toolkits?

Steven G. Parker wrote:

I think one side effect of the implementation is that manta's rendering loop iterates continuously. This is fine for benchmarking but we will certainly not want to continuously render the same image over and over for most applications.


For animating scenes, you do want it to update continuously. Also, if you stop the rendering there can be noticable latency in waking the threads back up when you want to start again. Nevertheless, there is a way in Manta - called an IdleMode. The idea is that you can register a component to do something when nothing is changing, like putting the workers to sleep. This capability needs a little more work but I think it is the right way to do it.

Would we ever want to render the exact same image twice in a row? Eventually the animation would end--or at least not need to be displayed.

Imagine a mechanical part that spins continuously, even though the animation could go on forever, if it is moved out of view of the camera, there is no longer a reason to keep refreshing the image.

In a shared environment, after I stop moving my camera, all of the processor time should be devoted to rendering frames for your camera.

Do we have an explicit model for control in Manta? If not, I would propose that manta work through a queue of transactions. These might alter the state of one channel pipeline or some global variable. The most basic assumption we can make is that transactions in the global queue, require all pipes to refresh, and transactions in the local queue only require a specific pipe to refresh. After all of the global and local queues are idle, the engine can stop rendering and wait for more input.

Abe




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