13.2 3D Texture Volume Rendering

Using 3D textures for volume rendering is the most desirable method. The slices can be oriented perpendicular to the viewer's line of sight, and close-up views can be rendered with spherical ``shell slices'' to avoid aliasing in the parts of the image that where sampled far from the direction of view.

 

Here are the steps for rendering a volume using 2D textures:

1. Load the volume data into a 3D texture. This is done once for a particular data volume.
2. Choose the number of slices, based on the criteria in Section 13.5. Usually this matches the texel dimensions of the volume data cube.
3. Find the desired viewpoint and view direction
4. Compute a series of polygons that cut through the data perpendicular to the direction of view. Use texture coordinate generation to texture the slice properly with respect to the 3D texture data.
5. Use the texture transform matrix to set the desired orientation the textured images on the slices.
6. Render each slice as a textured polygon, from back to front. A blend operation is performed at each slice; the type of blend depends on the desired effect. See the blend equation descriptions in Section 13.4 for details.
7. As the viewpoint and direction of view changes, recompute the data slice positions and update the texture transformation matrix as necessary.