Wednesday, August 19, 2009

Virtual Texturing part 2

A picture, or well in this case a movie, is worth more than a thousand words:


On top of the screen you can see (pages A/B) how many pages are used (A), and how many there are in memory (B).
The FPS / Ms should really be ignored..

Internally the OpenGL library for C# i'm working with (OpenTK, and i don't have the source-code) or a broken driver is forcing my app to sync to my monitor's refresh rate (60hz), and my recording software is seriously interfering with the timing of that syncing.

Update: putting a timer around the rendering code (and not relying on OpenTK's timer which is always synchronized to the monitors' refresh rate) showed that i was actually rendering around 4000-5000fps (0.2-0.3ms) instead of just 60fps ;)

Other than that there hasn't been any real performance optimalisations yet and i'm doing some things the quick & dirty way (readbacks are not async, page uploads are not async either, and should probably be spread out over multiple frames etc. etc.).
I'm basically just doing whatever i can to get things working like i want instead of trying to use the most optimal OpenGL api mechanisms at the moment.

Next to that there are still some artifacts there, i mean next to the usual video compression artifacts, which i'm trying to track down at the moment.
Just look at 0:30 to 0:32 in the bottom-left corner of the video.
It's weird that the page loading artifacts are there, because at the moment i'm uploading all the required pages before i use them.

The virtual texture is a mere 8192x8192 at the moment and completely in memory (no reading from disk at the moment).
Any larger texture would have to be loaded from disk, my system would probably not like loading a 16384x16384 texture in memory ;)

Filtering is trilinear, Bilinear would obviously be faster and would stress the system less as there are fewer pages to be required to be used per frame.
Seams between pages are more visible with bilinear filtering, but surprisingly hard to spot using trilinear filtering.. in fact, i haven't been able to spot a single one so far!

Next steps would be to fix all the artifacts, start reading back from disk, and optimizing everything.

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