Fill 2D area bound by vertices in XNA

Question

I'm learning XNA by doing and, as the title states, I'm trying to see if there's a way to fill a 2D area that is defined by a collection of vertices on a plane. I want to fill with a color, not a file-based texture.

For an example, take a rounded rectangle whose vertices are defined by four quarter-circle triangle fans. The vertices are defined by building a collection of triangles, but the triangles may not be adjacent.

Additionally, I would like to fill it with more than a single color -- i.e. divide the bound area into four vertical bands and have each a different color. You don't have to provide me the code, pointing me towards resources will help a great deal. I can be handy with Google (which I did try first, but have failed miserably).

This is as much an exploration into "what's appropriate for XNA" as it is the implementation of it. Being pretty new to XNA, I'm wanting to also learn what should and shouldn't be done on top of what can and can't be done.

Answer 1

Not too much but here's a start:

The color fill is accomplished by using a shader. Reimer's XNA Tutorials on pixel shaders is a great resource on the topic.

You need to calculate the geometry and build up vertex buffers to hold it. Note that all vector geometry in XNA is in 3D, but using a camera fixed to a plane will simulate 2D.

To add different colors to different triangles you basically need to group geometry into separate vertex buffers. Then, using a shader with a color parameter, for each buffer, set the appropriate color before passing the buffer to the graphics device. Alternatively, you can use a vertex format containing color information, which basically let you assign a color to each vertex.