dielectric_material node

In this scene, the bowl is created using the dielectric_material shader. This shader is commonly used for dielectric media such as glass, water, and other liquids.

Sample workflow for dielectric_material

1. Open the Hypershade editor. Under the Create tab, select Create mental ray Nodes. Click on dielectric_material under the Materials section to create the shader.
2. In the shader’s Attribute Editor, change Index of Refraction to 1.65. This is the index of refraction for a typical glass material.
3. Click on the dielectric_material1SG node. In the Attribute Editor, expand the mental ray section. Since photons are used in this scene (for caustics and global illumination, and so on), a photon shader needs to be added to the shader group. Under the Custom Shaders section, click

   

   for the Photon Shader attribute and select dielectric_material_photon (under the Photonic Materials section). This is the corresponding photon shader for the dielectric_material shader.
4. In the Attribute Editor, change the Index of Refraction for the dielectric_material_photon to also be 1.65. In this scenario, we wish to simulate both the appearance of glass and the caustic effect of glass. Therefore, the Index of Refraction for the dielectric_material and dielectric_material_photon shaders are set to identical values.

dgs_material node

The stand of the bowl is created using the dgs_material shader. This shader is commonly used to simulate glossy materials such as metals, mirrors, glossy paint and plastic, and so on.

Sample workflow for dgs_material

1. Open the Hypershade editor. Under the Create tab, select Create mental ray Nodes. Click on dgs_material under the Materials section to create the shader.
2. Click on the dgs_material1SG node. In the Attribute Editor, expand the mental ray section. Since photons are used in this scene (for caustics and global illumination, and so on), a photon shader needs to be added to the shader group. Under the custom shaders section, click for the Photon Shader attribute and select dgs_material_photon (under the Photonic Materials section). This is the corresponding photon shader for the dielectric_material shader.

Subsurface scattering node

The grapes in this scene are created using the subsurface scattering node. Subsurface scattering is usually used to create materials that scatter or absorb light internally (rather than reflect light at the surface). Using subsurface scattering, the grapes in the scene appear translucent and glowing.

mental ray for Maya includes several subsurface scattering nodes, for example, misss_physical, misss_fast_shader, misss_skin_specular, and so on.

misss_physical simulates subsurface scattering in the most realistic and physically accurate way. Alternatively, misss_fast_* provides a reasonable simulation of subsurface scattering, but allows for more efficient rendering and is easier to set up.

Sample workflow for misss_fast_simple_maya shader

1. Open the Hypershade editor. Under the Create tab, select Create mental ray Nodes. Click on misss_fast_simple_maya under the Materials section to create the shader.
2. Since subsurface scattering involves the bouncing of light near the surface, a lightmap must be attached to the shader. In the Hypershade editor, click misss_fast_lmap_maya under the Light Maps section to create the lightmap shader.
3. Click on the misss_fast_lmap_maya shader node. In the Attribute Editor, expand the Lightmap Write section and click for the Lightmap attribute to create a texture node.
4. In texture node’s Attribute Editor, check Writeable. Change the Filter Size Width and Filter Size Height to your render size. Change File Size Depth to 32 bits. Enter a file name in the Image Name attribute.
5. Click on the misss_fast_simple_maya material and map the misss_fast_lmap_maya shader to its Lightmap section.
6. Increase the number of samples in the Lightmap section to create a smoother effect. Increasing the number of samples would create more scattering and increase the intensity of the light gather effect. The scene thus has more glow.
7. Tweak the values under Algorithm control for better results.
   TipBeginning in Maya 8.5, you can also get the look of subsurface scattering in your scene by tuning the scatter attributes available in the mental ray section of the Anisotropic, Blinn, Lambert, OceanShader, Phong and PhongE surface material nodes. For more information regarding these scatter attributes, see Scattering and Work with Scattering.

   

Scene settings

1. Caustics should be incorporated in a scene that includes dielectric material. In the Render Settings window ( Window > Rendering Editors > Render Settings), select mental ray as your renderer. Under the mental ray tabs, Features tab, select Caustics under Rendering Features to enable the algorithm.
2. To incorporate caustics in the scene, the spotlight in the scene should emit photons. Expand the Caustic and Global Illumination section of the spotlight’s Attribute Editor. Check the Emit Photons section.
3. To brighten the scene, increase the Photon Intensity and the Exponent value in the spotlight’s attribute editor. If you only increase the photon intensity, this may significantly increase your rendering time. Lowering the exponent value allow you to brighten your caustics without increasing rendering time.
4. If you notice blobby caustics on the walls of your Cornell box, tweak the Filter type and Filter Size sections in your Render Settings window.