Use of Maya Attributes

Besides the Mai-Tai Globals dialog box, Mai-Tai gets much of its rendering options from Maya itself. It is important to understand which Maya attributes Mai-Tai uses and which it ignores.

Cameras

Projections

To decide whether to use an orthographic or perspective projection, Mai-Tai looks at the Orthographic box under Orthographic Views.

If it's an orthographic projection, Mai-Tai also uses Orthographic Width field to determine how large the image plane should be.

For perspective projections, Mai-Tai uses all of the following when choosing the field of view:

Camera Attributes: Angle of View, Focal Length, Camera Scale, Near Clip Plane
Film Back: Horizontal and Vertical Film Aperture, Film Aspect Ratio, Film Fit, Film Fit Offset, Horizontal and Vertical Film Offsets

For choosing the actual resolution, Mai-Tai looks at Film Fit, and Horizontal and Vertical Film Apertures.

Clipping

For setting clipping planes, Mai-Tai uses the Near Clip Plane and Far Clip Plane under Camera Attributes. If the Auto Render Clip Plane box is checked, the values are ignored and the extreme values of 0.001 and 10000 are used instead.

Motion Blur

Mai-Tai asks each camera if the motion of the camera should cause motion blur. Regardless of the answer, the camera's Shutter Angle (under Special Effects) is exported to control the amount of any kind of motion blur.

Depth of Field

Under Depth Of Field, if the Depth Of Field box itself is checked, Mai-Tai exports a RenderMan RiDepthOfField command and passes it the values of Focal Distance, F Stop, and Focus Region Scale.

Lights

All lights

Mai-Tai exports all of the Maya light types: ambient, directional, point, and spot. These lights have some things in common. The following attributes are exported to RenderMan regardless of the type: Intensity, Color, and Shadow Color.

In addition, Mai-Tai pays attention to which objects each light illuminates. Lights are "switched off" when exporting a primitive that is ignored by that light.

Ambient

Mai-Tai exports the Ambient Shade attribute by creating two RenderMan light sources, one ambient and one point. This attribute is unique to Maya ambient lights.

Non-ambient lights

All of Maya's non-ambient lights carry a decay rate. Mai-Tai exports this to RenderMan shaders that mimic the Maya lights.

Depth maps

Maya's non-ambient lights may all have depth maps. Mai-Tai examines the Use Depth Map Shadows check box to determine whether to make a shadow pass for each light. If it is checked, the Dmap Resolution, Near Clipping Plane and Far Clipping Plane are used.

Point lights may generate up to six depth maps, each one with a 90 degree field of view pointing in the directions of cube faces. The user may elect to skip some of these depth maps by unchecking Use X+ Dmap, Use X- Dmap, Use Y+ Dmap, Use Y- Dmap, Use Z+ Dmap, and Use Z- Dmap. This should be done when the user knows that no shadow will be cast in one or more of those directions.

Spot lights may also generate six depth maps, but more commonly, only one depth map is generated which matches the spot light's cone angle. To do this, check Use Only Single Dmap.

Directional lights always generate one depth map. Mai-Tai picks up the width from Dmap Width Focus.

When naming depth map files, Mai-Tai honors Dmap Name and Dmap Frame Ext.

Spot lights

Maya's spot lights have the most controls. Mai-Tai exports the Cone Angle, Penumbra Angle, and Dropoff. It also exports all of the Barn Door and Decay Region information. However, these special effects are currently unimplemented in the RenderMan shaders that come with Mai-Tai.

Primitives

All primitives

Mai-Tai exports Maya primitives of type Nurbs, Polygon, and NurbCurve. The following attributes are common to all of these primitives: Casts Shadows, Motion Blur, and Double Sided.

When generating shadow passes, Mai-Tai will only export primitives that are marked to cast shadows.

A primitive can only undergo transformational and/or deformational motion blur if the Motion Blur box is checked.

If backface culling is enabled in the Mai-Tai Globals, then primitives that are not marked as Double Sided will be selected for backface culling.

Shaders

Included with Mai-Tai are three RenderMan shaders to mimic Maya's lambert, blinn, and phong shaders. This section describes which parameters of these shaders are exported by Mai-Tai and which of those are actually implemented by the RenderMan shaders.

All shaders

For all three of the shaders, Mai-Tai exports the Diffuse Coefficient, Transparency color, Ambient color, Incandescence, Translucence, and Glow Intensity. Of these, the Transparency and Glow Intensity are currently unsupported by the shaders that come with Mai-Tai.

Blinn and Phong

For the blinn and phong shaders, Mai-Tai also exports the Specular Color and Reflectivity. Reflectivity is unsupported by the shaders.

Blinn takes Eccentricity and Specular Roll Off. Both are implemented by the shader.

Phong take Cos Power. It too is implemented.

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