I'm writing an application for a touch table using WPF and C#. (And, I'm not terribly familiar with WPF. At all.) We suspect we're not getting the framerate we're "requesting" from the API so I'm trying to write my own FPS calculator. I'm aware of the math to calculate it based on the internal clock, I just don't know how to access a timer within the Windows/WPF API.
What library/commands do I need to get access to a timer?
Although you could use a DispatcherTimer (which marshalls its ticks onto the ui thread, causing relativity problems), or a System.Threading.Timer (which might throw an exception if you try to touch any UI controls), i'd recommend you just use the WPF profiling tools :)
I think you're looking for the StopWatch. Just initialize it and reset it with each start of your iteration. At the end of an iteration, do your calculation.
First of all, are you aware that Microsoft provides a free diagnostic tool that will tell you the frame rate at which WPF is updating the screen? I guess if you're not convinced you're getting the framerate you're asking for, then perhaps you might not trust it, but I've found it to be a reliable tool. It's called Perforator, and it's part of the WPF Performance Suite, which you can get by following the instructions here: http://msdn.microsoft.com/library/aa969767
That's probably simpler than writing your own.
Also, how exactly are you "requesting" a frame rate? What API are you using? Are you using the Timeline's DesiredFrameRate property? If so, this is more commonly used to reduce the frame rate than increase it. (The docs also talk about increasing the frame rate to avoid tearing, but that doesn't really make sense - tearing is caused by presenting frames out of sync with the monitor, and isn't an artifact of slow frame rates. In any case, on Vista or Windows 7, you won't get tearing with the DWM enabled.) It's only a hint, and WPF does not promise to match the suggested frame rate.
As for the measurement technique, there are a number of ways you could go. If you're just trying to work out whether the frame rate is in the right ballpark, you could just increment a counter once per frame (which you'd typically do in an event handler for CompositionTarget.Rendering), and set up a DispatcherTimer to fire once a second, and have it show the value in the UI, and then reset the counter. It'll be somewhat rough and ready as DispatcherTimer isn't totally accurate, but it'll show you whether you've got 15fps when you were expecting 30fps, for example.
If you're trying to get a more precise view (e.g., you want to try to work out whether frames are being rendered constantly, or if you seem to be getting lost frames from time to time), then that gets a bit more complex. But I'll wait to see if Perforator does the trick for you before making more suggestions.
You want to either wrap the win32 timing calls you'd normally call (such as QueryPerformanceCounter), by using p/Invoke, or use something in .NET that already wraps them.
You could use DateTime.Ticks, but it's probably not high enough resolution. The Stopwatch class uses QueryPerformanceCounter under the covers.
If you want something that's reusable on a lot of systems, rather than a simple diagnostic, be warned about processor related issues w/ QPC and Stopwatch. See this question: Can the .NET Stopwatch class be THIS terrible?
