Question

I’m having problems making smooth animations in GDI+. The problem as I understand it from Googling is that there is some kind of bug with the clock-ticks in .NET on a multi-core processor. Here’s a simplified version of what I’m doing:

class Animation
{
  System.Diagnostics.Stopwatch sw = new Stopwatch();
  float AnimationTime = 1000; //time it takes the animation to complete

  public bool IsComplete
  { get { return sw.ElapsedMilliseconds > AnimationTime; } }

  public void StartAnimation()
  {
     sw.Reset();
     sw.Start();
  }

  public void DoFrame()
  {
     float PercentComplete = (float)sw.ElapsedMilliseconds / AnimationTime;
     //draw the animation based on PercentComplete
  }
}

DoFrame() is called like this:

Animation.Start();
do
{
  Animation.DoFrame();
  Application.DoEvents();
} while (!Animation.IsComplete);

The problem is that the animation is very smooth for about 15 frames then it jerks, it actually goes backward (sw.ElapsedMilliseconds gives a lesser value than the previous query). It’s very annoying and it’s ruining my otherwise smooth animation that looks great even on a Core 2 Duo (despite Microsoft saying this is a multicore bug). I have an i7 and the animation is smooth except for 2-3 frames per second that look “jerky”.

I understand that this is a known issue and Microsoft blames it on the processor, so my question is, does anyone know any kind of solution for this? I tried using a Kalman filter and it sort of works. I was hoping maybe there is an established “correct” solution for this?

Oh b.t.w. I tried using DateTime instead of Stopwatch and got the same results.

I also tried:

double PercentComplete = (double)sw.ElapsedTicks / (double)Stopwatch.Frequency * 1000 / AnimationTime

It gives me the same results.

Answer 1

It probably has to do with the way you call DoFrame(). Using the following windows forms / GDI+ based algorithm you should alway get very smooth animations:

const double desiredFps = 500.0;
long ticks1 = 0;
var interval = Stopwatch.Frequency / desiredFps;
while (true)
{
    Application.DoEvents();
    var ticks2 = Stopwatch.GetTimestamp();
    if (ticks2 >= ticks1 + interval)
    {
        ticks1 = Stopwatch.GetTimestamp();

        // do the drawing here
    }
}