Introduction to the Global Illumination Function of Viz Artist

Introduced in Viz Artist 3.9, Real Time Global Illumination allows you to create Lightmaps and Ambient Occlusion maps that are modifiable in real time. This technique is based on the lightmap functionality widely used in leading game engines. When activating GI, you need to specify the computation settings, and precompute the Global Illumination and Ambient Occlusion maps. In Viz Artist, you find this feature section Scene Settings > Global Illumination. The details of the settings are described below.

Working with Global Illumination

In general, Global Illumination requires two UV sets on any geometry that should be computed with GI: one UV set used for texture mapping, and one UV set used to create Lightmaps. There are two ways to create the Ligtmap UVs to get GI working properly. You can either import an .fbx-file with two UV sets that you have created by yourself. The first UV set must be used for texture mapping, and the second UV set is only used for Lightmaps. Or, you can use the first UV set (UV for texturing), and let the GI system calculate the according UVs for Lightmaps.

Global Illumination has an advanced algorithm that can extract the UV coordinates of your first UV set, and automatically create UVs for the Lightmaps. The better the layout of your unwrapped UVs for texture mapping are, the better the GI system can generate the Lightmaps based on this information. The most efficient way is to create your own UVs for Lightmaps. Here, it is important to have your UV layout in the range from 0 to 1. Also, all UVs for Lightmaps must be unique and non-overlapping, otherwise GI cannot compute all Lightmaps. In general, the layout of the UVs for Lightmaps look different than the layout of UVs for texture mapping. There are several tutorials available online concerning how to create UVs for Lightmaps.

The following is an example of correct UV Layout for Lightmaps. In the image below, you see the UV layout of the second UV channel, which is used for lightmaps only.

Precomputed Lightmaps do not use any memory on your GPU, so the texture memory of Viz is not reduced when having Lightmaps computed. The Lightmaps are not visible on your objects/geometries in the scene tree, as they are applied to the rendering pipeline in the render window.

Global Illumination Settings

Creating a Scene with Global Illumination

First, you need to import a geometry or scene with proper UVs and normals. This can be either just one UV set with unwrapped UV coordinates to be able to do a proper texture mapping and extract the lightmaps from this UV set. You can also import an .fbx-file containing the second UV set, with a layout for lightmaps created in your preferred 3D application. On your imported geometries make sure the normal orientation is facing outwards, flipping the normals with the Expert plug-in leads to wrong computation results. Do not forget to turn Auto Mesh Classification on or off, depending on your existing UV sets.

Next, if your scene is not already modeled or imported with the proper size, you need to set up the real world size of your scene before you do the baking. Then place some lights in your scene. After this, adjust all the parameters described above and run a test bake, to see if you get any error messages concerning UVs or baking. If your render passes look good from the debug views, no error messages appeared, or at least no visual errors are visible, you can start working on the detailed light setup.

All the light setups, color, type, transformation, can be done at any time now, without a need to recompute the whole scene. This is the benefit of working with lightmaps. It is very important to increase the radiosity setting of the lights that light up the whole scenery, using the Light Editor. Be aware that Lightmaps are static maps that react in real time to the GI parameters. They are not dynamically calculated with animations. When you have an object, like the Cornell box example above, and animate the rotation of one of the cubes inside the Cornell box, you see the wrong colors reflected during the rotation. This is because the lightmaps are statically projected onto geometries. When rotating the middle cube of the Cornell Box example, which is receiving a green color from the green wall next to it, it does not turn red when rotating to the other side, because lightmaps are static. The same applies to Ambient Occlusion maps. Whenever you want to animate an object, you should not compute the lightmaps or Ambient Occlusion maps for it, as otherwise the result does not look correct. If an object is hidden in the Scene Tree, it is not calculated with GI.

After setting up all the parameters and running a successful precomputation process, switch to the Indirect Light debug view from the Global Illumination pane, to see how the radiosity intensity of the light affect your scene. Experiment with different lights and radiosity settings to get your desired result. During this process, you should switch between the debug view for Indirect Light and Normal Mode, to see how much GI affects in your scene. Now, you can start refining your scene with adding Substance Shaders to your scene to increase realism. Compared to using regular plain textures, substance's light reflection is aiming a physical correct behavior depending on the shader properties. This is something a regular texture does not do.

If you want to work with plain textures only, this is possible. Be aware that no other material and effect shaders than Substance Shaders are supported in combination with Global Illumination.

To get your light color correctly spread into your scene, you need to apply a material to every geometry and use the eye dropper tool of the material editor to get the correct color from the texture or shader used on the selected geometry. Otherwise, radiosity cannot blend the surface color into the set, since it is not possible to extract the color directly from textures or shaders. Applying a material with color does not influence the Substance Shader, as this material color is only used for the color bleeding of the radiosity.

Limitations

Global Illumination is built to work in conjunction with Physically Based Rendering (PBR) materials, to get the most realistic results. In general, it is common to use Global Illumination in conjunction with Substance shaders. Substance shaders are the only available PBR shaders for Viz Artist. Therefore, any other material shader, such as RTT and others, does not work with Global Illumination. When using a feature which is not supported by Global Illumination, you get an error message in the scene info. Error messages in the scene info are indicated by a red info icon.

The following list are examples of features and/or plug-ins that are not supported in combination with Global Illumination:

• RTT Shaders

• Softmask

• Framemask

• ImageMask

• Fluid Effect

• Water Shader

• Drop Shadow

• Emboss

• Anisotropic Light

• Cartoon Shader

• Gooch Shader

• Lighting Shader

• Normal Map

• Filter Blend

• Filter Blur

• Filter Color Balance

• Filter Radial Blur

• Filter Sepia

• Filter Sharpening

• HDT