3D Material Parameters
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Dialog Box: 3D Material Properties [ 3D Display Parameters dialog]

In the 3D Display mode the material properties of objects determine the way the objects interact with the light sources.

The color observed at a given point is a resultant of the light source and the material properties; that is, the RGB coefficients of the Ambient , Diffuse and Specular components of the light source(s) are multiplied by the specified colors of the objects, and by the material coefficients in this dialog, then the results are limited to the range 0.0-1.0. See Lighting Equation for details. In SHAPE, there is only one light source, color white, which has rays coming from a constant direction (parallel rays), rather than from a single point.

Ambient light has no direction or origin and is considered to bathe all objects uniformly. Having a significant ambient component causes non-illuminated parts of objects to be other than black. It thus "softens" the illumination in a somewhat similar way to the Darkest Shade and Darkness Angle parameters (Shading dialog) in the Standard display mode.

Diffuse color is usually the main component of the appearance of objects. The intensity of the color is dependent on the angle between the light ray and the normal to the surface in question.

Specular reflection only occurs when the normal to the surface in question is close to bisecting the angle between the incident light and the vector from the point on the surface to the eye. It produces bright highlights on a curved surface. The larger the Shininess coefficient, the smaller will be the bright specular highlight on a curved surface. The shininess coefficient has a maximum of 128 because of computational restrictions, but values on the order of 5-30 are usually realistic.

In SHAPE, specular reflection is always white, that is it does not depend on the color of the object, only the color of the light source (which is white). Specular reflection does not currently work well for crystal faces and mirror planes because faces at the reflection angle will give an essentially solid white appearance, rather than a bright spot. This is because the angle is calculated for the corners of the face, and interpolated for each point in the interior of the face. In order to produce bright-spot highlights on flat surfaces, it would be necessary to subdivide the surface on a fine grid, and use point light sources rather than parallel illumination.

Emission is similar to ambient, except that there is no dependence on the color of any light source. A high value of emission can make an object look like is is glowing.

These material properties are specified separately for cylindrical edges and symmetry axes, and for crystal faces and mirror planes.