Building Layered Shading Networks 

Use Slim to Create Layered Shaders, with a Unique Shader Space for Each Layer.

Introduction  - Building a Layered Shader with Slim

The layered shader is a powerful tool for constructing Slim Shading networks. The layered shader allows you to layer several different surface models over each other (i.e. blinn over metal over plastic, etc) using a variety of different compositing blends. 

In this tutorial, we will walk through the process of creating a layered shader by building a shading network of a Slim beach ball. 

1. First we'll add the stripes to the ball, as the first layer. 

2. Next we'll add a second layer to the image of Slim on top of the stripes, using a second layer. We'll apply the image using a planar-Z projection.

3. When we're done, we'll have something like the image on the right. 

 
The Slim Beach Ball.

Creating a Layered Shader

1 -  Open the Tutorial Scene 

For this tutorial, open the following scene file : 
mtor/ scenes/ layered_shader/ball.ma

(Where are the scene files?)

In this scene we have a ball and a MTOR coordinate system. We'll use the coordinate system to position a planar-Z projection on the ball.

The Maya scene.

2 - Render the Scene

You should get a gray ball. This is the gray shader is the default color of the ball, just waiting for a new layered shader.

The ball with a default shader.

 

3 - Create a Layer Shader

Next we'll create a layer shader and build the first layer.

Create a new Slim palette.
RenderMan-> Slim-> New Palette

Next create a layered shader.
File-> Create Appearance-> Layer

Open the layer in the appearance editor by double-clicking it in the palette. Next add a layer by clicking on the "Add Layer" button. ( ) 

Now connect a Matte shading model to the new layer by clicking on the pull down menu (  ) and selecting "Matte."

Create a new palette and a new layer.

Create a layered shader and attach a Matte 

4 - Construct a Layer for the Stripes

Open the matte in the Appearance editor, by clicking on the "Matte" connection. ( )  

With the Matte open,  we'll connect an image file to the SurfaceColor parameter. There we'll add a stripe texture. We can connect an image file by switching the parameter's provider from "internal" ( )  to "connection" (  ) and then selecting "ImageFile" from the color pull-down menu 
(). 

Connect an ImageFile to the Matte's surface color.

With the ImageFile now open, open the file picker by clicking on the file picker icon ( ) and select "stripes.tif" from the images directory.

Next we must convert the texture. From the texture menu ( )  select: Convert-> Convert Textures. This provides us with the proper syntax needed to convert the image. For this image the syntax is [txmake images/stripes.tif].

Now we'll attach an ST manifold to the ImageFile, applying our texture to the natural parameterization of the object. To create the connection, select ST from the manifold pull-down menu.( ) 

 

Select and convert a striped texture

5 - Render the Ball with New Stripes

It should be similar to the example on the right. Try rendering the nodes to make the colored icons appear, if you haven't done so already. To do that, select the nodes by dragging a lasso around them (Red boxes will appear around selected nodes), and type "r" (for render icons).

Now render from the RenderMan menu, like we did above. You should get an image similar to the one on the right, a ball with stripes.

This completes the first layer.

The shading network so far

The first layer completed

5 - Add a New Layer

We've successfully added the stripes. Now we'll project an image of Slim onto the ball.

For the next step we'll add a second layer. We'll use the second layer to project an image of Slim over the stripes.

To add a new layer, open the Layer in the appearance editor and clicking the add layer button ( ).  Then from the connection menu ( ) connect another Matte. We'll use this matte to create a planar-Z projection. Your setup should resemble the image.

Notice the "Over" pull-down menu, which provides a variety of different blends. In our case, the default "over" is fine. 

Add a new layer and connect a matte

6 - Construct the Second Layer

To start building the second layer, open the new Matte in the appearance editor.

With the Matte open, add a new ImageFile to the SurfaceColor parameter from the color pull-down menu ( ) like we did above.

With the ImageFile now open, open the file picker by clicking on the file picker icon ( ) and select "slim.tif" from the images directory.

Next we must convert the texture. From the texture menu 
( ) select: Convert-> Convert Textures. This automatically provides us with the proper syntax needed to convert the image, in the case the syntax is [txmake images/stripes.tif].

Finally, connect a Projection manifold from the pull-down menu ( ).

Select and convert the texture, slim.tif, and connect a projection.

The default settings are basically all we need for a planar-Z projection. However, we could also create other types of projections (spherical, box, cylindrical, etc.) by changing the settings.

Next, we must complete the projection by attaching a SurfacePoint manifold to the Projection. This allows us to define a coordinate system for the projection. 

You can connect one from the Manifold pull-down menu. We'll use the SurfacePoint to define where the projection is placed in the scene, by filling in the name of a coordinate system.

Connect a SurfacePoint manifold

With the SurfacePoint open, enter the name of the coordinate system into the Space parameter (see image on the right). We want to call our coordinate system "SlimShape", so we'll enter that, we'll also add a little syntax that will make things easier. So we enter: 
[coordsys SlimShape] 

Next we need to rename our coordinate system in the scene. It has its default name. Generally it's a good idea to rename coordinate systems to something more sensible. Select the coordinate system in Maya and rename its shape node to "SlimShape" like the image shows. 

Notice that the SurfacePoint requires the shape name and not the object name. 

Enter the name of the coordinate system

Rename the coordinate system in the scene

7 - The Second Layer so Far - Needs Transparency

Take a look at the shading network in the graph editor, like we did above. We can see the second layer.

However, if you render the swatch of the layer, the top node in the hierarchy, we can see that the second layer completely covers the first layer. 

To fix that we'll add transparency to the second layer, so the stripes of the beach ball are visible. Then we'll be finished with the shader.

The shading network with two layers

The second layer lacks transparency

8 - Adding Transparency to the Second Layer

Open the open the top node of the second layer (the matte) in the appearance editor.

Connect a FloatToColor to the SurfaceOpacity like we did above (by switching the provider from internal to connection and then selecting FloatToColor from the pull-down menu).

Add a FloatToColor to the Matte's opacity

Connect an ImageFile float

Notice that we're using the alpha channel of the original texture. The Channel parameter determines which channel we take from the image (R, G, B, luminance, or alpha, to name a few). By using the ImageFile Float (as opposed to the ImageFile Color), we can select any channel we want. 

Now remember to convert the texture to a file format PRMan can read. From the texture menu select: 
Convert-> Convert Textures. 

Finally, connect the first projection manifold from the pull-down menu. In this case our original projection was called "Projection_0" and we can select that from the bottom of the manifold pull-down menu. 

By sharing the projection node we can control the placement of both images (defining color and alpha transparency) with a single projection and coordinate system. 

Import the image and connect it to the first projection

9 - The Final Shading Network

When we render the scene we see the texture of Slim placed over the stripes of the beach ball.

 
The final shading network with two layers

A rendering of the final shader

10 - Exercise: Adding a Third and Fourth Layer

As an exercise, try adding another layer, with its own manifold. 

In the image here, a metal has been laid on top of the first two layers and a fractal has been used to modify the opacity. 

There's many different effects that can be created using layered shaders.
Have fun! 

An example of additional layers