Programming WPF, 2nd Edition

Textures

Because DiffuseMaterial, SpecularMaterial, and EmissiveMaterial are based on brushes, we need not be limited to plain colors for our surfaces. We are free to paint 3D objects with gradient brushes, bitmaps, or drawings. We can even use any part of a user interface as a brush with which to paint a 3D object. An image or pattern used to paint a 3D surface is often referred to as a texture.

To use a textured material, we must tell WPF exactly how the brush should be positioned on the surface. With a solid color, this is a nonissue—the entire surface is of uniform color. But with a bitmap, we need to specify exactly where the image is projected onto the surface.

MeshGeometry3D provides the TextureCoordinates property for exactly this purpose. For each 3D point in the Positions, you can specify a 2D texture coordinate. Example 17-17 defines a simple square surface with four points, joined together with two triangles.

Example 17-17. MeshGeometry3D with TextureCoordinates

<MeshGeometry3D Positions="−1,1,0  1,1,0  −1,−1,0,  1,−1,0"
                Normals="0,0,1  0,0,1  0,0,1  0,0,1"
                TextureCoordinates="0,0  1,0  0,1  1,1"
                TriangleIndices="0,2,3  0,3,1" />

Figure 17-26 shows the texture coordinates specified for each corner of the square, and how the TriangleIndices collection joins these together with triangles. Texture coordinates are specified in the coordinate space of the brush's Viewport. As we saw in Chapter 13, by default tile brushes use a mapping mode of RelativeToBoundingBox, which means that their ...