Updating with Variable or Fixed Timing

Article
09/29/2011

Demonstrates how to set up the runtime to call your Update method using variable or fixed timing.

There are two techniques for setting how often your Update method is called. Variable timing means to call Update as soon as other work finishes; this implies that it is up to a game developer to ensure that your render loop happens quickly enough so that Update will be called often enough to exceed your minimum frame rate. Fixed timing means that Update is called each time a fixed interval of time has passed. Fixed timing guarantees that Update will be called, however, so you may drop frames if the previous work needs to be interrupted to call Update.

Complete Sample

The code in this topic shows you the technique. You can download a complete code sample for this topic, including full source code and any additional supporting files required by the sample.

Download AppModelDemo_Sample.zip.

Updating with Variable Timing

To use a variable time step

Create a class that derives from Game.
Set IsFixedTimeStep to false.

This causes the Update method to be called as often as possible, instead of being called on a fixed interval.
```
this.IsFixedTimeStep = false;
```

Updating with Fixed Timing

To use a fixed time step

Create a class that derives from Game.
Set IsFixedTimeStep to true.
```
this.IsFixedTimeStep = true;
```
This causes the Update method to be called each time the fixed time interval has passed.
Set TargetElapsedTime to a fixed interval of time.

This example sets the time between calls to 16 milliseconds.
```
this.TargetElapsedTime = new TimeSpan(0, 0, 0, 0, 16);    // Update() is called every 16 milliseconds
```