Environment Shaders

This section shows a basic workflow to use environment shaders.

References:

mental ray User Manual, Chapter 3.12.

mental ray Shaders Guide, Chapter 1.3.

Rendering with mental ray, Chapter 4.7, Appendix C

Where to find environment shaders
Material shaders appear in the Hypershade > Create mental ray Nodes > Environments.

The following environment shaders are shipped with Maya:

• mib_lookup_background
• mib_lookup_cube1
• mib_lookup_cube6
• mib_lookup_cylindrical
• mib_lookup_spherical

Default behavior

The proper connection for an environment shader is:

• from environmentShader.message to shadingEngine.miEnvironmentShader.
• from environmentShader.message to cameraShape.miEnvironmentShader.

Ctrl+drag from a material shader to a shading engine to make the above connection.

Image based lighting (under Image Based Lighting in the mental ray Render Globals) feature introduced in mental ray for maya 6.0 works in a similar way to mib_lookup_spherical, but with more features and simpler workflow.
In this section, we explore the workflow for setting environment mapping using mib_lookup_spherical.

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 the template scene we will use for this section: environment_start.ma.

Render with mental ray.

environment_start.ma

As shown in the image, the two spheres on the left are reflective.
The reflection is achieved by using mib_reflect. Please read sampleCompositing.html if you are not familiar with this shader.
Environment mapping would not be applied unless the material is reflective.

Step 2. Local environment map

First, let's try a local environment map, which applies to a given material (or shading engine) only.
If the ray leaving an object with the material does not intersect anything, the color from the environment shader is returned.

• Open the Attribute Editor of red_SG.
  In the mental ray section, you can find Environment Shader.
  An environment shader connected to this port is applied to objects with this shading engine only.
• Click the map button next to Environment Shader and select mib_lookup_spherical. Rename the shader to "red_env".
• Open the Attribute Editor of red_env.
  tex is the image to use for this shader. Click the map button. The button creates a mentalrayTexture node, and connects to the shader.
  Rename the texture node as red_tex.
• From the Attribute Editor of the texture node red_tex, choose an image file to use. Choose checker.iff for example.
  
  

Now Render with mental ray.

The checker is sphere mapped to the red sphere.

Local environment map

· reflect attribute of mib_reflect shader decides the contribution from the reflection. Decreasing the value means less contribution from the environment.

· Turn on notrace of red_reflect to disable any other reflection than the environment.

Render again, and notice the sphere has a less obvious checker pattern, and no reflection of the red ball.

Local environment map

Notice also that the yellow and the blue balls are not affected by the environment shader of the red ball, except the reflection of the red ball on it.

Step 3. Global environment map

Another way of using an environment shader is to connect it to a camera shape.
Environment shader connected in this way is used by a primary ray that did not hit anything.
It's similar to image plane in Maya. (mib_lookup_background is closer to image plane.)
If an object has reflective material, the environment shader affects the reflection, as long as the material does not have its own environment shader.

• Create a mib_lookup_spherical, and name it "camera_env" .
• Create a new mentalrayTexture node for the shader by clicking the button next to tex.
• Then choose a image, carbon_raport.rla in sourceimages directory for example.
• Ctrl Drag and drop camera_env to perspShape . Check the connection from camera_env.message to perspShape.miEnvirionmentShader.
  
  

Render.

Local and global environment map

• Notice that the background is filled with camera_tex. As camera_env is connected to perspShape, the global environment shader only affects rays originated from the persp camera. If render from different camera, the background is black.
• Now the ball in the middle has reflection from the environment. For an environment mapping to affect a material, the material should be reflective. The yellow sphere as mib_reflect connected to the material shader (yellow_phong), whereas the blue sphere has a phong shader only.
• The red sphere on the left, in the other hand, has its own environment shader, and is not using the global environment map at all. Instead, the local environment mapping overrides the global one.

environment_finish.ma shows the final state of this tutorial.