> For the complete documentation index, see [llms.txt](https://docs.flatredball.com/flatredball/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.flatredball.com/flatredball/api/microsoft-xna-framework/graphics/renderstate/referencealpha.md).

# 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.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://docs.flatredball.com/flatredball/api/microsoft-xna-framework/graphics/renderstate/referencealpha.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.