Add constant latency to graphical output in XNA 4

does anyone know of an easy way to add a constant latency (about 30 ms) to the graphical output of an XNA 4 application?

I want to keep my graphical output in sync with a real-time buffered audio stream which inherently has a 开发者_开发技巧constant latency.

Thanks for any ideas on this!

Max

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If you really need to delay your graphics, then what you could do is render your game to a cycling series of render-targets. So on frame n you display the frame you rendered at frame n-2. This will only work for small latencies, and requires a large amount of additional graphics memory and a small amount of extra GPU time.

A far better method is not to delay the graphical output at all, but delay the audio that is being used to generate the graphical output. Either by buffering it or having two read positions in your audio buffer. The "audio" read being X ms (the latency) ahead of the "game" read.

So if your computer's audio hardware has 100ms of latency (not uncommon), and your graphics hardware has a latency of 16ms: As you are feeding the sample at 100ms into the audio system, you are feeding the audio sample at 16ms into the your graphics calculation. At the same time, the audio from 0ms is hitting the speakers, and the matching graphic is hitting the screen.

Obviously this won't work if the thing generating the graphical output is also generating the audio. But the general principal of both these methods is that you have to buffer the input somewhere along your graphics chain, in order to introduce a delay that corresponds to the one you are experiencing for audio. Where along that chain it is easiest to insert a buffer is up to you.

For latencies of <100ms, I wouldn't worry about it for most games. You only really care about this kind of latency for audio programs and rhythm games.

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I might not understand the question, but couldn't you keep track of how many times update is called and mod 2? 60fps mod 2 is 30...