Getting elapsed time between updates in wxWidgets

Question

I am builing an interactive application using the latest wxWidgets(3.0.1) and OpenGL(3.3) on Windows. I have gotten to the point where I have a wxGLcanvas rendering onto a wxPanel and it works fine. The rendering is done in the paint event for that GLcanvas. However, I now want to perform simulations with an accurate delta time between updates.

So essentially I would like some sort of functionality that would allow me to have a method like

void Update(float dt)
{
  // Update simulation with accurate time-step
}

I have come across timers but I'm not sure how I could incorporate it into my application to get an accurate dt. Some have mentioned creating a separate thread for that panel to update independently from the rest of the application. Is this an option and roughly how is it implemented if that is the case?

score 0 · Answer 1 · answered Aug 26 '14 at 01:24

Timer precision should be good enough to achieve at least ~50 FPS, so they should be good enough for your purpose. You need to use a timer to get regular calls to your timer event handler which can then use a more accurate method (as timers are not guaranteed to be perfectly regular) to determine whether an updated is needed, e.g. using wxDateTime::UNow(), and queue a Refresh() in this case.

Notice that you still will not be able to guarantee regular window refreshes using normal GUI frameworks.

ravenspoint · Answer 2 · 2014-08-26T12:48:57.093

0

What operating system are you using? There is no way in Windows to guarantee an accurate time for an event. Unix, however is a real time operating system ( RTOS ) and it is possible to guarantee event times.

What range of delta times do you care about? The distinction between RTOS's and Windows only matters for times less than 2 to 3 milliseconds ( unless windows becomes ridiculously overloaded ) Since any worthwhile 3D scene will take more that 3 milliseconds to render, this is probably a non-issue!

Of most significance in this kind of question is the response time of human vision. Watching a dynamic diagram such as a plot, people are unaware of any refresh rate faster than 300 ms. If you want to attempt a video realistic effect, you might need a refresh rate approaching 25 ms - but then your problem will not be the accuracy of your timer, but the speed of your scene rendering. So, once again, this is a non-issue.

edited Aug 26 '14 at 12:48

answered Aug 26 '14 at 12:43

ravenspoint

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I'm using windows. Ive edited the question to display ths OS in question – John Aug 26 '14 at 13:16
I'd like to have rougly a 16-17 ms between updates so 60fps essentially – John Aug 26 '14 at 13:19
Can you render your scene in 16 ms? – ravenspoint Aug 26 '14 at 13:48
Yeah I can.. Is it a matter of creating a timer and calling timer.Start(16) ?? – John Aug 26 '14 at 15:40
Yes. Your timer event handler will be called every 16 ms +/- 5 ms. http://stackoverflow.com/a/571935/16582 – ravenspoint Aug 26 '14 at 15:43
So in the timer event handler I could call update like this Update((float)(16/1000)). – John Aug 26 '14 at 17:45
Yes, I suppose. ( Note that the integer division will pass 0 to the update method - you would be better to just use a constant.) – ravenspoint Aug 26 '14 at 17:54

Getting elapsed time between updates in wxWidgets

2 Answers2