Radiosity Rendering

Let's assume you have a scene ready, and that you want to render it with the Radiosity Rendering. The first thing to grasp when doing Radiosity is that no Lamps are necessary, but some meshes with Emit material property greater than zero are, since these will be the light sources.

You can build the test scene shown in , it is rather easy, just make a big cube, the room, give different materials to the side walls, add a cube and a stretched cube within and add a plane with an non-zero Emit value next to the roof, to simulate the area light (Figure 2).

You assign Materials as usual to the input models. The RGB value of the Material defines the Patch colour. The 'Emit' value of a Material defines if a Patch is loaded with energy at the start of the Radiosity simulation. The "Emit" value is multiplied with the area of a Patch to calculate the initial amount of unshot energy.

TipEmitting faces
 

Check the number of "emittors" on Blender console! If this is zero nothing interesting can happen. You need at least 1 emitting patch to have light and hence a solution.

Figure 2. Set-up for Radiosity test.

When assigning materials be sure that all of them have the Radio toggle on to enable the material for Radiosity calculations (Figure 3).

Figure 3. Radiosity enabled material

Please note that the light emission is governed by the direction of the normals of a mesh, so the light emitting plane should have a downward pointing normal and the outer cube (the room) should have the normals pointing inside, (flip them!)

Switch to the Radiosity Buttons . The Button window is shown in (Figure 4).

Figure 4. Radiosity buttons for radiosity rendering.

The Collect Meshes starts the Radiosity Modelling tool, don't use it now.

The neighbouring buttons defines:

Set the Max Iterations: to 100 and turn to the Rendering Buttons Window (F10)

Locate the Radio Tog Button (Figure 5) and press it, then Render! (F12).

Figure 5. Enabling Radiosity in the Rendering Buttons.

The rendering will take some more time than usual, in the console you will notice a counter going on. Result will be quite poor (Figure 6, left) because the automatic radiosity render does not do adaptive refinement!

Select all meshes, one after the other, and, in EditMode subdivide it at least three times. The room, which is much bigger than the others, you can even subdivide four times. Set the Max Iterations a bit higher, 300 or more. Try again the Rendering (F12). This time the rendering will take even longer but the results will be much nicer, with soft shadows and colour leaking (Figure 6, right)

Figure 6. Radiosity rendering for coarse meshes (left) and fine meshes (right).

Note

In the Radiosity Rendering Blender acts as for a normal rendering, this means that textures, Curves, Surfaces and even Dupliframed Objects are handled correctly.