Texture Shaders - bump mapping

This section shows how to use bump maps on mental ray shaders.

This is a little more complex, compared to other shaders, because the base shaders do bump mapping with a shader called mib_passthrough_bumpmap, which is intended to be called in a shader list before the material shader is called. The shader modifies the normal in the state so that the material shader works with the modified normal. However, shader lists in materials are not supported yet in mental ray for Maya.

The work around is to use the mib_color_mix shader to call the mib_passthrough_bumpmap shader before the material shader is called.

References:

See mental ray User Manual, Chapter 3.2.

mental ray Shaders Guide, Chapter 1.2.

Rendering with mental ray, Chapter 4, Appendix C.

Step 1. Getting Ready
Make sure the mental ray for Maya plug-in is loaded.

· Windows > Settings/Preferences > Plug-in Manager...

· Find Mayatomr and check loaded

Open textureShaders_bump_start.ma.

This scene has a sphere, a plane and a spot light. Note that the spot light uses mental ray light shader – a physical light with very high intensity.

textureShaders_bump_start.ma

Step 2. Floor

• Let's assign a dgs_material to the floor
• Select the shading engine of the floor, floorSG.
• From the Attribute Editor of floorSG, open mental ray section.
• Go to Custom Shaders section.
• Click the map button next to Material Shader.
• From the Create Render Node bar, choose mental ray tab.
• Select dgs_material from the Materials section.
• Rename dgs_material1 to floorMat.
• Check the connection between the shader and the shading engine. Material shaders are connected to shading engine's miMaterialShader by default.
• Change the parameters of floorMat.

Step 3. Ball

• Assign another dgs_material to the ball
• Create a dgs_material from Hypershade > Create mental ray Nodes > Materials.
• Rename it to ballMat.
• Connect ballMat to ballSG.miMaterialShader – CTRL+MMB drag ballMat to ballSG.
• Adjust the shader parameters.
• Render with mental ray.

Dgs_materials

Step 4. mib_passthrough_bump_map

Now we are going to add a bump map to the ball.

• Create a mib_passthrough_bump_map shader from Hypershade > Create mental ray Nodes > Textures.
• Select mib_passthrough_bump_map1 node and open the Attribute Editor.
• First, we have to set Bump Effects section:
• Set factor to 8.
• Create a bump_basis node from Hypershade > Create mental ray Nodes > Textures.
• Connect mib_bump_basis1.u to mib_passthrough_bump_map1.u, mib_bump_basis1.v to mib_passthrough_bump_map1.v,
• MMB drag mib_bump_basis1 to mib_passthrough_bump_map1.
• From the Connection Editor:
• Select U from the left pane, U from the right pane.
• Select V from the left pane, V from the right pane.
• Second, we need to adjust the Texture Coordinates section.
• Only coord needs to be adjusted, and the rest can be left untouched for now.
• We are going to connect mib_texture_vector.outValue to mib_texture_remap.input, and mib_texture_remap.outValue to mib_passthrough_bump_map1.coord.
• See mental ray User Manual, Chapter 3.2 Coordinate Systems, and mental ray Shaders Guide, Chapter 1.2 Texture Space Mapping, for more details.
• Create a mib_texture_vector node from Hypershade > Create mental ray Nodes > Textures.
• Set selspace to 1, meaning object space.
• Create a mib_texture_remap node from Hypershade > Create mental ray Nodes > Textures.
• MMB drag mib_texture_vector1 to mib_texture_remap1, and select input .
• MMB drag mib_texture_remap1 to mib_passthrough_bump_map1, and select coord .
• Finally, we can assign a file texture for bump mapping.
• Select mib_passthrough_bump_map1 and open its Attribute Editor again.
• In the mental ray Texture section, click the map button next to tex.
• This button creates a mental ray file texture node, and opens its Attribute Editor.
• From the Attribute Editor of mentalrayTexture1, choose a file for bump mapping.
• In this scene, we use carbon_raport.rla in sourceimages directory.

Step 6. Using mib_color_mix to use shader list

• Create a mib_color_mix node from Hypershade > Create mental ray Nodes > Data Conversion.
• Connect mib_passthrough_bump_map1 to mib_color_mix1.color_base.
• Open mib_color_mix1 attribute editor
• MMB drag mib_passthrough_bump_map1 to color_base attribute of mib_color_mix1,
• Open mib_color_mix1 Attribute Editor
• Set num to 1 , as we have only one input.
• Set mode_0 to 1 to set compositing mode to mix.
• Set weight_0 to 1 to set weight of color_base to 1.
• Connect mib_color_mix1.outValue to ballMat.specular
• Select ballMat and open the Attribute Editor.
• MMB drag mib_color_mix1 to specular attribute of ballMat.

Step 7. Finish
Now all the connections are made.

Select mib_color_mix1 node and check input output connection.
Render with mental ray.

The bump map is applied to dgs_material.
If you do not see the bumps, check the shading network connections in textureShaders_bump_finish.ma.

dgs_material with bump.

textureShaders_bump_finish.ma

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