Phong MAT

Summary

The Phong MAT creates a material using the Phong Shading model. It has support for textures, reflections, bumps, cone lights, rim lights, alpha maps and more. You can output its GLSL shader into two DATs for further adaptation in a GLSL MAT by using the Output Shader parameter.

Phong Shading models three types of reflected light:

• Ambient - Ambient is considered light that does not come from any particular direction and is therefore constant across the surface. In the physical world, ambient light is created from the reflection of light off surfaces in the environment.
• Diffuse - Diffuse models the light reflected by matte surfaces. This light is reflected equally in all directions, therefore the position of the observer does not effect the percieved illumination.
• Specular - Specular models the light reflected by glossy surfaces. This light is reflected mainly in the direction of the reflected ray and is attenuated by the 'shiny-ness' of an object. Since the light reflected from the surface is mainly in the direction of the reflected ray, the position of the observer determines the specular highlight on the surface.

NOTE: We see the color of an object because of the color of light that the material reflects.

Phong Shading produces very nice specular highlights, although it is still an approximation and not physically accurate. Contrasting with the Gouraud shading model that calculates the lighting at each vertex and interpolates the value across the polygon, Phong calculates the lighting at each pixel.

To see how all of the different parts are summed together by looking at the Phong Lighting Equation article.

phongMAT_Class

Parameters - RGB Page

Parameters - Alpha Page

Note: Simply applying alpha to an object does not make it transparent. For more information refer to the Transparency article.

Parameters - Multi-Texturing Page

On the Multi-texturing page of the Phong material, you can have up to 4 texture maps and choose any of the 8 possible texture coordinates for each map. By default the texture maps are multiplied together, but there is a field for a custom GLSL code that can be used. Here's how that works:

The 4 texture maps are referred to in the parameter by t0, t1, t2 and t3 respectively. So the default equation if all 4 texture maps are used is: t0 * t1 * t2 * t3. You can use and constants and other math operators, so for example t0 + (t1 * 0.5) is valid. If they refer to a map that doesn't exist, the shader won't compile correctly (e.g. using t3 when it isn't set or the TOP doesn't exist).

They can also refer to specific components of the texture using .r .g .b and .a. So for example if you want to do t0 over t1, the expression would be:

t0 + (t1 * (1.0 - t0.a))				

The output from your expression must be a vec4, so for example:

 t0.rgb + t1.rgb // Error				
 vec4(t0.rgb + t1.rgb, 1.0)  // Works				

The alpha from the result of these maps is used.

Parameters - Rim Page

Other rim lights have the same parameters, internal parameter names just have a different number instead of 1.

Parameters - Advanced Page

Parameters - Deform Page

Refer to the Deform Article for more information on doing deforms in TouchDesigner.

Parameters - Common Page

Blending

Blending is summing the color value of the pixel being drawn and the pixel currently present in the Color-Buffer. Blending is typically used to simulate Transparency. The blending equation is: Final Pixel Value = (Source Blend * Source Color) + (Dest Blend * Destination Color)

Depth Test

Depth-Testing is comparing the depth value of the pixel being drawn with the pixel currently in the Frame-Buffer. A pixel that is determined to be in-front of the pixel currently in the Frame-Buffer will be drawn over it. Pixels that are determined to be behind the pixel currently in the Frame-Buffer will not be drawn. Depth-Testing allows geometry in a 3D scene to occlude geometry behind it, and be occluded by geometry in-front of it regardless of the order the geometry was drawn.

For a more detailed description of Depth-Testing, refer to the Depth-Test article.

Alpha Test

Alpha-testing allows you to choose to draw or not draw a pixel based on its alpha value.

Wire Frame

The wire-frame feature will render the geometry as wire-frame, using the actual primitive type used in the render. What this means is surfaces like Metaballs, NURBs and Beziers will become a wire-frame of the triangles/triangle-strips used to render them (since these types of primitives can't be natively rendered in OpenGL).

Cull Face

The cull face parameter will cull faces from the render output. This can be used as an optimization or sometimes to remove artifacts. See Back-Face Culling for more infomation.

Polygon Depth Offset

This feature pushes the polygons back into space a tiny fraction. This is useful when you are rendering two polygons directly on-top of each other and are experiencing Z-Fighting. Refer to Polygon Depth Offset for more information. This is also an important feature when doing shadows.

Info CHOP Channels

Extra Information for the Phong MAT can be accessed via an Info CHOP.

Common MAT Info Channels

Common Operator Info Channels

• total_cooks - Number of times the operator has cooked since the process started.

• cook_time - Duration of the last cook in milliseconds.

• cook_frame - Frame number when this operator was last cooked relative to the component timeline.

• cook_abs_frame - Frame number when this operator was last cooked relative to the absolute time.

• cook_start_time - Time in milliseconds at which the operator started cooking in the frame it was cooked.

• cook_end_time - Time in milliseconds at which the operator finished cooking in the frame it was cooked.

• cooked_this_frame - 1 if operator was cooked this frame.

• warnings - Number of warnings in this operator if any.

• errors - Number of errors in this operator if any.

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