Multitouch Game Loop Input Processing

21 Jan 2011 19:37
Last Modified
13 Jan 2013 18:13

There are multiple potential sources of input for an XNA game component, such as keyboard, gamepad, mouse, Surface multitouch, .NET 4 Touch, etc. Dealing with multpile approaches to gathering input in the Update loop of each component can become complex, and adding support for a new input type further adds to this complexity.

I divided my input handling into two different categories:

  1. Controller-based input such as keyboard and gamepad.
  2. Manipulation-based input such as mouse, Surface multitouch, and .NET 4 touch.

For the latter, I wanted to abstract input handling such that a given game component only had to deal with a custom Manipulator type. In this way, I would be free to change or add input source(s) without affecting the implementation in a game component.

Clearly, different input sources provide different types and degrees of information. Surface multitouch Contacts for example, provide information on size, orientation, type etc, whereas a mouse only provides position. In many cases only position information is necessary, however additional properties can easily be added to the Manipulator type and supported by a game component if available. In this case I decided to sub-class my Manipulator type to the following:

  1. Mouse and finger-touch
  2. Surface Tag contacts
  3. Surface blob contacts

In order to deal with multitouch manipulations, I could process input using my previosuly-discussed Manipulation classes and processor.

The following video demonstrates the use of multiple input sources:

Video 1. Input processing from multiple sources.

Since a mouse can only deliver single-touch input, when demonstrating mouse input in Video 1 I switch the pivot type to "Tracked" in order to be able to demonstrate rotation and scaling, as shown in Figure 1.

Manipulation Input

Figure 1. Input processing from multiple sources.

Of course, it is unlikely that a scenario mixing both Mouse and Surface input would ever be used in practice, however it serves to illustrate how a game component can handle input in a consistent way, without being aware of the input source. For example, the buttons on the left of the screen are "pressed" using either Surface v1 Contact or a mouse-click, however the buttons only tracking Manipulator state.

A useful application of this approach is the ability to write XNA applications which work with both Surface v1 multitouch input and .NET 4 multitouch (and mouse for single-touch if multi-touch hardware is not available) without any code changes, i.e. multi-platform targetting.

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