Displaying pre-distorted webcam images

"lazydodo" wrote:
I'd say measure how long the warping shader takes , no need to sink a pile of time and money in custom lenses if you're saving your self a only few microseconds. If it run in the milliseconds sure it's worth a shot but i'd be really surprised if that was the case.

Well, you might say that, but on my (slow) laptop, turning on the image warp caused a drop of 2-3 fps (out of something that was about 15-21 to start with.)

That means compared to running without warp, 20 fps became about 17.

20 fps = 50 milliseconds per frame
17 fps = 58.8 milliseconds per frame.

My system is way too slow to be representative, but an extra 8 milliseconds of rendering time (or about 15%) is pretty big.
Now, rendering time isn't equal to latency, but unless your rendering engine has some creative workarounds in it, the overall latency consists of:
input hardware latency + input processing latency + Rendering latency + Screen output latency.

So... an extra 15% rendering time is a definite, and substantial increase in latency.

(of course, if other hardware is more efficient at calculating the warping it might be less than that, and also if you render at 60 fps, it would imply you could render at 69 fps without the warping, but also that the warp process itself adds about 2.5 milliseconds to the rendering of each frame.)

So... It would seem the image warp (unless it's vastly more efficient on newer hardware), would only start to become insignificant once you reach about 240 fps or so... But at those kinds of speeds the entire rendering process itself starts to look like an insignificant fraction of overall latency.)