Timer?

There are two main approaches to timers:

• Polling, where you continuously check whether the time period has passed. You can use System.Diagnostics.Stopwatch or System.DateTime.Now to create such a timer.
• Event-based, where you register an event handler to be called at some future time. You can use System.Threading.Timer to register such a callback.

First, you need to decide what kind of accuracy you need:

• Stopwatch provides sub-millisecond precision, but may drift over larger time spans.
• DateTime.Now and Threading.Timer are stable over larger time spans, but lose accuracy under tens of milliseconds.

Use a Stopwatch for accurate measurements over a few seconds. Use DateTime.Now as a wall clock (for example, to measure total gameplay time). Use Threading.Timer to schedule an event to be fired in the future (just take care that the event is fired in a new thread, so don't write OpenGL code directly inside the handler).

Am I right in thinking Stopwatch is syncronous and Timer calls an asyncronous thread aswell? Or can stopwatch be used to invoke a separate thread on a delegate?

The 2.0 BCL provides three event-based and two polling-based timer implementations.

Event-based:

• System.Windows.Forms.Timer: objarni covered this one. Just stay away (it won't even work with the GameWindow).
• System.Timers.Timer: accurate, asynchronous (the event is raised in a background thread). Appears to be relatively heavy, but has more features than other timers.
• System.Threading.Timer: accurate, lightweight, asynchronous (the event is raised in a ThreadPool thread).

Verdict: use System.Threading.Timer, unless you need more features (in that case, check out System.Timers.Timer). Avoid System.Windows.Forms.Timer, unless you are writing a GUI application.

Polling-based:

• System.Diagnostics.Stopwatch: Accurate, precise, suitable for short time-periods.
• System.DateTime.Now: stable over large time-periods.

Verdict: use Stopwatch if you need sub-second precision; use DateTime.Now otherwise.

You can use "e.Time" in GameWindow.UpdateFrame and RenderFrame to get the elapsed period since the last UpdateFrame/RenderFrame event respectively. This is based on Stopwatch, hence accurate, but don't use it to measure large time spans.

If I recall correctly, CheatCat wanted a timer to control animation. Solution: use e.Time from UpdateFrame event:

protected override void UpdateFrame(FrameEventArgs e)
{
    // Simple jump calculation
    if (Keyboard[Key.Up])
        Player.Velocity = new Vector(0, 20, 0);  // 20 m / s, direction: up
 
    // Simple movement calculation. Can get numerically unstable over time,
    // though it's generally not a problem in practice.
    Player.Velocity += Gravity * e.Time;     // Gravity is defined as Vector(0, -10, 0) m / s^2
    Player.Position += Player.Velocity * e.Time;
}

By playing around with the values, you can get nice results with very little work.