XNA & EXTENSION METHODS 2

Continuing with the topic of how to use the handy functionality provided by "Extension Methods" with our XNA-based creations, for this article we are going to need the "FuelCell" tutorial (remember that you shall find this tuto -along with the "TopDownShooter" one- in the help file under the "What's New In This Release" section).

Ok. In the chapter called "Finishing Touches" of the FuelCell' s tutorial, you'll find the following method at the very end of the "FuelCellGame.cs" file:

private Rectangle GetTitleSafeArea(Viewport viewport)
{
Rectangle retval = new Rectangle(viewport.X, viewport.Y, viewport.Width, viewport.Height);

#if XBOX
retval = viewport.TitleSafeArea;
#endif

return retval;
}

If you remember my last article on the subject, you'll be anticipating by now that the Viewport struct could be "extended" so as to retrieve its "unsafe" area with one method call.

If so, you guessed it right! We can use Extension Methods to declare an operation called, say "GetFullArea", and give it the proper implementation.

Not only can we pass again a parameter by reference (using the "out" reserved word) -like we did in Part 1 of this series- but also in this particular case, since we're dealing with a struct, we can afford to implement an overloaded method that locally declares, creates and returns an instance of a Rectangle (I know what you're thinking, but unfortunately, there are no "Extension Properties" in C#, so we need to get the rectangle from a method call).

Using Extension Methods, our solution should look like the following:

using System;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;

namespace MyNamespace.Math
{
public static class MathExtensions
{
public static void GetFullArea(this Viewport viewport, out Rectangle area)
{
area = new Rectangle(viewport.X, viewport.Y, viewport.Width, viewport.Height);
}

public static Rectangle GetFullArea(this Viewport viewport)
{
return new Rectangle(viewport.X, viewport.Y, viewport.Width, viewport.Height);
}
}
}

Now, the GetTitleSafeArea(...) method could be re-implemented like this:

private Rectangle GetTitleSafeArea(Viewport viewport)
{
Rectangle retval;

#if XBOX
retval = viewport.TitleSafeArea;
#else
viewport.GetFullArea(out retval);
#endif

return retval;
}

Or also like this:

private Rectangle GetTitleSafeArea(Viewport viewport)
{
#if XBOX
return viewport.TitleSafeArea;
#else
return viewport.GetFullArea();
#endif
}

Remember two important things:

• You'll have to add the proper "Using" statement in the file that will use the extension method (in my example: "MyNamespace.Math"), and
• You'll have to manually add a reference to the "System.Core" assembly in your project.

This technique can be used to get, say -among other things, a Vector2 containing the width and height of the Viewport (as well as for the display and the client area). I leave it as an exercise for you to try (you'll see it's actually quite easy to implement).

I hope you find this article useful.

'till next time,
~Pete