Define a fog shader with a program that modifies the Cf, Of, or Af values to simulate atmospheric effects.
The purpose of a fog shader is to modify the Cf, Of or Af variables after the surface shader has completed its shading. You can use illuminance statements inside fog shaders.
Globals
| Time (read-only) | The time at which the shading occurs, as a number from 0 (shutter open) to 1 (shutter close). |
| dPdz (read-only) | Floating point step size for volume rendering. |
| P (read-only) | Position of the point on the surface being shaded. In light or shadow shaders, the P variable contains the point on the light source. |
| Ng (read-only) | Geometric normal for the surface. This normal represents the “true” normal of the surface being shaded. For example, with Phong shading, the N variable represents the interpolated normal, while the Ng variable represents the true polygon normal. |
| L (read-only) | Vector from the point on the surface to the light source. The length of this vector represents the distance to the light source. |
| dPds (read-only) | Change in position with respect to the parametric s. |
| Pz (read-only) | Z component of the point being shaded. |
| I (read-only) | Direction from the eye to the point being shaded. This may or may not be a normalized vector. |
| Of | Final opacity for the surface. A value of {1,1,0} will be opaque in red/green, but let through blue light from behind. See opacity vs. alpha . |
| Eye (read-only) | Position of the eye. |
| dPdt (read-only) | Change in position with respect to the parametric t. |
| Cf | Final color for the surface. The vector represents the RGB color . |
| t (read-only) | Parametric t (sometimes called v) coordinate of the surface being shaded. |
| N (read-only) | Shading normal for the surface. |
| Cl | Light color. |
| s (read-only) | Parametric s (sometimes called u) coordinate of the surface being shaded. |
| Af | Final alpha for the surface. This is the value which is placed in the alpha channel of the output image. See opacity vs. alpha . |