III.6.3 Acoustic Radiance Transfer - first phase
Acoustic radiance transfer is a technique that combines the basic radiosity model and BRDFs. The main difference is that the responses at the surfaces are now spatially discretized and instead of storing a single response at a patch there are several, as can be seen in the illustration below.

- Move the source around to investigate the BRDFs at each patch. Most of them are specularly reflective whereas some others, such as the audience area, have a large diffuse component as well.
- You can change the BRDF's of individual patches by stepping through the patches, and tuning the absorption and diffusion, or by selecting a random BRDF for the patch. The current patch is highlighted.

Patch size: Absorption: Diffusion: BRDF discretization:
Visualize: All energy Unshot energy

The basic radiosity algorithm presented above can be directly applied in this technique as well. The difference lies in the shootEnergy function and how it handles reflections.

Algorithm: Shooting the energy from a patch to all the other patches using BRDFs

This algorithm iterates over all the outgoing reflection angles in the response. It divides the energy to outgoing spatially discretized slots according to the BRDF, that is a function of two angles, incident and reflection angles. In addition, there is a need for a function getAngle that returns the angle in which the former patch sees the latter one. Note that this is not a symmetrical function, and, thus, there is a need to compute this for both possible orders of the patches.

As already mentioned, it is not possible to accurately model specular reflections with this approach that uses spatially discretized BRDFs and responses. Increasing the BRDF discretization to cover those is not possible in practice due to increase in memory requirements. For this reason, the acoustic radiance transfer is best suited for such applications in which the early specular reflections are not essential or it can be used in a hybrid model in which it is combined with some other technique, such as the image-source method.