18.2. Radiosity Rendering

Relevant to Blender v2.31

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 an Emit material property greater than zero are required, since these will be the light sources.

You can build the test scene shown in Figure 18-1, it is rather easy. Just make a big cube for the room, give different materials to the side walls, add a cube and a stretched cube within it, and add a plane with a non-zero Emit value next to the roof, to simulate the area light (Figure 18-2).

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 'emitters' on Blender console! If this is zero nothing interesting can happen. You need at least one emitting patch to have light and hence a solution.

Figure 18-2. Set-up for Radiosity test.

When assigning materials be sure that all of them have the Radio toggle on to enable the Shader Panel of the Material subcontext buttons (Figure 18-3).

Figure 18-3. 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 sub-context of the Shading Context. The Panels, shown in Figure 18-4, are two: Radio Rendering which governs Radiosity when used as a rendering tool (present case) and Radio Tool, which governs Radiosity as a modelling tool (next section).

Figure 18-4. Radiosity buttons for radiosity rendering.

The buttons define:

Set the Max Iterations: to 100 and turn to the Scene Context and Render Sub-context (F10).

Locate the Radio Tog Button (Figure 18-5) in the Render Panel and set it 'on' to enable Radiosity, then Render! (F12).

Figure 18-5. Enabling Radiosity in the Rendering Buttons.

The rendering will take more time than usual, in the console you will notice a counter going up. The result will be quite poor (Figure 18-6, left) because the automatic radiosity render does not do adaptive refinement!

Select all meshes, one after the other, and in EditMode subdivide them at least three times. The room, which is much bigger than the other meshes, you can even subdivide four times. Set the Max Iterations a bit higher, 300 or more. Try Rendering again (F12). This time the rendering will take even longer but the results will be much nicer, with soft shadows and colour leakage (Figure 18-6, right).

Figure 18-6. Radiosity rendering for coarse meshes (left) and fine meshes (right).


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