AutoCAD 2008 User's
Guide > Create Realistic
Images and Graphics > Render 3D Objects
for Realism > Basics of
Rendering >
Material Adjustments
Adding materials to objects greatly increases the realism of a model.
In the context of rendering, materials describe how an object reflects or transmits light. Within a material, maps can simulate textures, bump effects, reflections, or refractions.
From the Advanced Render Settings palette, you can turn materials on or off, turn material filtering on or off, and affect how the surfaces of an object are rendered.
Materials that you’ve created and attached to objects in the model are normally turned on when you start the rendering process. If you turn them off, all the objects in the model assume the characteristics of the GLOBAL material.
You can control whether texture filtering, pixel averaging used in anti-aliasing, occurs when the model is rendered.
When texture filtering is turned on, the renderer uses a pyramidal filtering methods, which applies filtering as a function of distance.
There is a slight rendering cost when texture filtering is active. Pyramidal filtering requires memory allocation equal to approximately 133% of the size of a texture map. Compared to the detail and realism provided by texture mapped materials, rendering performance is not impacted that much.
When texture filtering is turned off, no anti-aliasing occurs to texture maps when the renderer processes the model.
Since you have no control over the direction that faces, normals are pointing, you may encounter a model that has flipped normals. The back sides of faces are invisible to the renderer. This means that the face appears to be missing when viewed from the back. Objects are usually created with the surface normals facing outward, but it is possible to create objects with the faces flipped or to import complex geometry in which the face normals are not properly unified.
When Force 2-Sided is active, both sides of faces are raytraced as shaded. While this incurs a slight increase in rendering time, it is often faster than trying to fix multiple instances of flipped faces.
