referencealpha

Introduction

The ReferenceAlpha is a value that is used to test whether a pixel should be drawn according to its alpha value. The default value for this is 0. This is used in combination with the AlphaFunction property.

Usage

The following code results in all pixels being drawn:

FlatRedBallServices.GraphicsDevice.RenderState.AlphaFunction = CompareFunction.GreaterEqual;
FlatRedBallServices.GraphicsDevice.RenderState.ReferenceAlpha = 0;

In the code above, any alpha value greater than 0 will be drawn. In the following code, only alpha values greater than 128 (out of 255) will be drawn:

FlatRedBallServices.GraphicsDevice.RenderState.AlphaFunction = CompareFunction.GreaterEqual;
FlatRedBallServices.GraphicsDevice.RenderState.ReferenceAlpha = 128;

FlatRedBall XNA uses an alpha range of 0 to 1 (inclusive). This gets converted to a 0 to 255 range, so you may need to perform some math to convert between the two systems.