RAT Tutorial: Maya Attributes

Introduction - Maya Attributes
Shaders in Slim can be controlled from Maya by linking shader parameters to Maya Attributes. This provides a direct connection from Maya to practically any shader parameter desired. This high level of integration allows you to link any animated parameter, defined by a Maya curve, to drive any shader parameters. The implementation required is straightforward, requiring just a snippet of tcl, a very non-intimidating tidbit. Once understood, this technique is invaluable to getting the most out of MTOR, for it allows you to truly immerse your shaders in a Maya scene. In this lesson we'll explore some of the possibilities of driving shader parameters with Maya Attributes. For this tutorial you'll want to be familiar with Maya concepts like Arbitrary Variables and creating Set Driven Keys.
In this Lesson We'll use a arbitrary Maya Attribute to animate shader parameters in Slim. To demonstrate this we'll turn a light on and off.
On In this scene we'll use one Maya attribute to control the intensity of the light (centered in the bulb), the surface glow of the bulb shader, and the intensity of the "fake" glow around the light itself.	Off The same Maya Attribute will be used to increase the intensity of the blue lighting in the background.
On	Off
Driving Shader Parameters with Maya Attributes 1 - Open the Maya Scene
For this tutorial, open the scene: */mtor/scenes/mayaAttr/light_bulb.ma* (Where are the scene files?) Looking at the scene, We see a bare bulb hanging in the middle of the room. Now let's turn it on and off . . .	The Maya Scene
2 - Select the Bulb Light
Next select the light source inside the light bulb geometry. It is called "bulb." An arbitrary variable has been attached to the bulb called "OnOff". This variable has been animated in this scene. If you play through the animation the light will go on and then flash off. This "OnOff" attribute is used to drive the intensity of this light as well, using Maya's set driven key.
An Arbitrary Attribute has been used to drive the Intensity of the Light in the Maya Scene
3 - Render the Scene
When the scene is rendered, we get something like this…however now none of the parameters will animate. So we need to link the parameters of these shader to the Maya "On Off" attribute.	The Scene Rendered
4 - The Palette
In this palette we'll drive the following aspects of these parameters. 1) Bulb: The surface shader of the light bulb. The incandescence will be animated. 2) Bulb Glow: This creates a fake glow around the light. This glow will be animated. 3) Bulb Light: This illuminates the scene. The intensity will be animated. 4) Blue Light: When the main light is turned off, these will turn on. The intensity will also be animated, but in the inverse.
5 - Animate the Light Intensity
To connect the attribute to a parameter, open the "bulb_light" light shader in the attribute window. Switch the KI, intensity, provider to "expression," so you have an orange provider (as seen in the image on the right). Now enter the following: [mattr "bulbShape.OnOff" $f] That's it! Now this parameter is driven by the Maya Attribute To explain . . . mattr - Stands for Maya Attribute "bulbShape.OnOff" - is our arbitrary attribute. $f - Is important, as it says to return this value every frame.	[mattr "bulbShape.OnOff" $f]
6 - Set the Other Parameters
We can animated multiple parameters with a single Maya Attribute. We'll demonstrate that now. Be sure to switch the provider from Internal to Expression.

Bulb: Animate the incandescence with: [mattr "bulbShape.OnOff" $f]

Bulb Glow: For the bulb glow open the shader and go to the CombineColors connected to the Opacity. Animate the bulb of the glow with: [mattr "bulbShape.OnOff" $f]

Blue Light: Now we'll get a little tricky. We'll animate the lights so they increase in intensity as the other parameters decrease. We can do this by creating a slightly more complex expression: *.135 (1-[mattr "bulbShape.OnOff" $f])**
7 - Render with the Light Out
The "OnOff" parameter is at zero at frame fifty. Go to frame 50 and render. You should see your parameters are now driven by the "OnOff" attribute. You could animate the sequence for extra kicks.	Frame 50, with "OnOff" at zero.

Maya Attributes

In this Lesson