Using GraphicsDevice.Viewport.Project with a small farPlaneDistance

Question

I am using "GraphicsDevice.Viewport.Project()" to create a "3D" waypoint system like so;

I have a farPlaneDistance of 5000 in my camera;

objProjectionMatrix = Matrix.CreatePerspectiveFieldOfView(MathHelper.ToRadians(45.0f), flAspectRatio, 1.0f, 5000.0f);

Obviously when the waypoint is farther than 5000, it cant find it within the viewport and bugs out. Is there another way to display waypoints on screen (within a 3D world) without using GraphicsDevice.Viewport.Project()?

Or, is increasing my z buffer out to 100,000 not that big of an issue (i find this hard to believe)?

Learning as I go, Thanks in advance!

Linuxx

Answer 1

The problem with a large farPlaneDistance is floating point errors. This can cause things to draw in the wrong order because multiple verts are getting are falling withing the values that a float can re-present.

I recommend doing something like the below to lock the object a certain distance from the camera if it is too far away.

var location = Vector3.Subtract(object.Vector3, camera.Vector3);
if (location.length > 5000) {
    location.normalize();
    location.Multiply(5000)
    object.Vector3 = Vector3.Addition(camera.Vector3 + location);
}

Another common solution is to use point sprites but they are not supported in XNA 4.0.