The lighting module maintains a stack of current lights, the ambient light level, and a material.
When using the lighting module directly, each element of input data to the lighting module (the D3DLIGHTINGELEMENT structure) contains a direction vector and a position (for positional light sources such as point lights and spotlights).
Two lighting models—monochromatic and RGB—are supported. The color fields are always placed after the D3DLIGHTINGELEMENT structure in the D3DLIGHTDATA structure.
The monochromatic lighting model (sometimes also called the "ramp" lighting model) uses the gray component of each light to calculate a single shade value. The RGB lighting model produces more realistic results, using the full color content of light sources and materials to calculate the lit colors.
For materials with no specular component, the shade is the diffuse component of the light intensity and ranges from 0 (ambient light only) to 1 (full intensity light). For materials with a specular component, the shade combines both the specular and diffuse components of the light according to the following equation:
This shade value is designed to work with precalculated ramps of colors (either in the hardware's color-lookup table or in lookup tables implemented in software). These precalculated ramps are divided into two sections. A ramp of the material's diffuse color takes up the first three-quarters of the precalculated ramp; this ranges from the ambient color to the maximum diffuse color. A ramp ranging from the maximum diffuse color to the maximum specular color of the material takes up the last quarter of the precalculated ramp. For rendering, the shade value should be scaled by the size of the ramp and used as an index to look up the color required.
A packed RGB color is defined as the following:
#define RGB_MAKE (red, green, blue) \
((red) << 16) | \
((green) << 8) | \
(blue))
A packed RGBA color is defined as the following:
#define RGBA_MAKE(red, green, blue, alpha) \
(((alpha) << 24) | \
((red) << 16) | \
((green) << 8) | \
(blue))
Colors in Direct3D are defined as follows:
typedef unsigned long D3DCOLOR;
The type of the light must be one of the members of the D3DLIGHTTYPE enumerated type: D3DLIGHT_DIRECTIONAL, D3DLIGHT_POINT, D3DLIGHT_PARALLELPOINT, D3DLIGHT_SPOT, or D3DLIGHT_GLSPOT. This enumerated type is part of the D3DLIGHT structure. Another member of this structure is a D3DCOLORVALUE structure, which specifies the color of the light. The values given for the red, green, and blue light components typically range from 0 to 1. The value for the ramp lighting model is based on the following equation:
Each of the color values can fall outside of the 0 to 1 range, allowing the use of advanced lighting effects (such as dark lights). The direction vectors in the D3DLIGHT structure describe the direction from the model to the light source. This vector should be normalized for directional lights. All vectors should be given in world coordinates; these vectors are transformed into model coordinates by using the current world matrix, allowing the efficient lighting of models without the need to transform the vectors into world coordinates. For point lights and spotlights, the range parameter gives the effective range of the light source. Vertices that are outside this range will not be affected by the light. The intensity of the light is modified by a quadratic attenuation factor, where d is the distance from the vertex being lit to the light, as shown in the following equation:
The remaining members of the D3DLIGHT structure (dvTheta and dvPhi) are used for spotlights to define the angles of the umbra and penumbra cones, respectively. The falloff factor (dvFalloff) is applied between the umbra and penumbra cones of the spotlight.
There are two types of methods for the lighting module, those that set the state of the lighting module, and those that use the lighting module directly to act on a set of points.
Like the transformation module, the lighting module can also be called directly. The D3DLIGHTDATA structure is used for all the direct lighting functions.