This reference page is linked to from the following overview topics: Principal Light Classes.

Detailed Description

See also:: Class RenderData, Class LightRayTraversal, Class ObjLightDesc, Class ShadeContext, Class Color, Class Point3.

Description:: This class has a method Illuminate() used to determine the color and direction of the light striking the point sc.P() and a method to get the position of the light. It also has two public data members that determine if the diffuse and specular colors of objects are affected.

Data Members:: BOOL affectDiffuse;

This data member is available in release 2.0 and later only.

If TRUE the light affects the diffuse color; otherwise it does not.

BOOL affectSpecular;

This data member is available in release 2.0 and later only.

If TRUE the light affects the specular color; otherwise it does not.

BOOL ambientOnly;

This data member is available in release 3.0 and later only.

If TRUE the light affects the ambient color only; otherwise it does not.

DWORD extra;

This data member is available in release 3.0 and later only.

This is not currently used and is available for use in the future.

#include <imtl.h>

Inheritance diagram for LightDesc:

[legend]

List of all members.

Public Member Functions
	LightDesc ()
virtual BOOL	Illuminate (ShadeContext &sc, Point3 &normal, Color &color, Point3 &dir, float &dot_nl, float &diffuseCoef)
virtual Point3	LightPosition ()
virtual CoreExport void	DeleteThis ()
Public Attributes
BOOL	affectDiffuse
BOOL	affectSpecular
BOOL	ambientOnly
DWORD	extra

Constructor & Destructor Documentation

LightDesc ( ) [inline]

Remarks:: Constructor. The affectDiffuse and affectSpecular data members are set to TRUE.

{ affectDiffuse = affectSpecular = TRUE; ambientOnly = FALSE; }

Member Function Documentation

virtual BOOL Illuminate	(	ShadeContext &	sc,
		Point3 &	normal,
		Color &	color,
		Point3 &	dir,
		float &	dot_nl,
		float &	diffuseCoef
	)		`[inline, virtual]`

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Remarks:: This method is called to determine the color and direction of illumination from the light that is hitting the point (sc.P()).

Parameters:

ShadeContext& sc

Describes the properties of the point to shade. The point itself is sc.P().

Point3& normal

The normal to the surface in camera space.

Color& color

The color that is returned. This is the brightness of light striking the point (sc.P())

Point3 &dir

The direction that the light is coming from.

float &dot_nl

This provides a bit of optimization as most lights will have to calculate this quantity. This is the dot product between the light vector and the normal to the surface.

float &diffuseCoef

This parameter should be set by the Illuminate function. The default value is the same as dot_nl. It will be used by shading functions instead of dot_nl to compute the diffuse illumination of the surface. The built-in lights use the new "Contrast" parameter (which has a range of [0..100]) to compute the diffuseCoef from the dot_nl by the Contrast function:

            // precomputed:
            float a = contrast/200.0f + 0.5f;                 // so "a" varies from .5 to 1.0
            kA = (2.0f-1.0f/a);
            kB = 1.0f-kA;
            
            // called by Illuminate() to compute diffuseCoef from dot_nl.
            float ContrastFunc(float nl)
            {
            // the "Bias" function described in Graphics Gems IV, pp. 401ff
                return (contrast==0.0f)? nl : nl/(kA*nl+kB);
            }

Returns:: Returns FALSE if the hitpoint is outside the effective range of the light or if the normal of the surface faces away from the light. This is a hint to the material that the light did not calculate its illumination because it is assumed it wasn't going to be used. If TRUE the point is being illuminated.