US 5,313,568 AGranted

Three dimensional computer graphics employing ray tracing to compute form factors in radiosity

AssigneeHewlett-Packard Company

InventorsJohn R. Wallace, Kells A. Elmquist, Eric A. Haines

Life of this patent

Estimating the term…

Loading patent…

Abstract

A method for rendering a three-dimensional image on a computer graphics display device involving the steps of providing a data base defining at least the geometry and reflectivity of light emitters and object in the scene and approximating surfaces of each object in the scene as patches in three dimensional space. Each patch is approximated as one or more elements defined by vertices. A source of irradiated light in the scene is selected and defined as a light source. Then, for each vertex, a form factor representing the fraction of light energy that arrives at the vertex from the source is determined by ray tracing from the vertex to the source. Radiosity is then determined at each vertex based on the form factors determined for each vertex. This process is repeated a selected number of times using a different light source each time. In this manner a plurality of radiosities are determined that collectively indicate the global illumination of the scene. The scene is then displayed based upon these radiosities.

Claims25

Dependent claims

A method of rendering, in a computer, and displaying on a computer graphice display device, a realistic three dimensional image of a scene, including realistic shading of objects in the scene by light emitters illuminating the scene, said method comprising the steps of:

a) creating a geometric model of a scene to be rendered and storing data representative of said geometric model as a database in the computer, said data including at least the geometry and surface reflectivity of the light emitters and the objects in the scene to be rendered;
b) approximating surfaces of each object in the scene as patches in three dimensional space, each patch being approximated as one or more elements defined by vertices;
c) selecting from the database a source of irradiated light in the scene, the selected source defining a light source, the light source being either one of the light emitters or an object that reflects light emitted by one of the light emitters;
d) determining, for each vertex, by ray tracing from the vertex to the light source, a form factor that represents the fraction of energy leaving the light source and arriving at the vertex;
e) determining radiosity at each vertex based upon the form factors determined from step (d);
f) repeating steps (c)-(e) a selected number of times, each time for a different light source, to obtain a plurality of radiosities collectively indicating global illumination of the scene;
and,
g) controlling the computer graphics display device to display the three dimensional image of the scene based upon the radiosities determined from step (f).

5 more elements

A method of rendering, in a computer, and displaying on a computer graphics display device, a realistic three dimensional image of a scene, including realistic shading of objects in the scene by light emitters illuminating the scene, said method comprising the steps of:

a) creating a geometric model of a scene to be rendered and storing data representative of said geometric model as a database in the computer, said data including at least the geometry and surface reflectivity of light emitters and objects in the scene;
b) approximating surfaces of each object in the scene as patches in three dimensional space, each patch being approximated as one or more elements defined by vertices;
c) selecting from the database a source of irradiated light in the scene, the selected source of irradiated light being either one of the light emitters or a surface that reflects light emitted by one of the light emitters, the selected source defining a light source comprising a source surface having an area, said source surface comprising a plurality of sample points;
d) performing the following steps for each vertex:
i) determining, for the vertex, individual form factors for each of a selected number of sample points, each individual form factor being determined by ray tracing from the vertex to that sample point;
and
ii) summing the individual form factors and dividing by the selected number of sample points to produce a total form factor for the vertex;
e) determining radiosity at each vertex based upon the form factors determined in step (d) for each vertex;
f) repeating steps (c)-(e) a selected number of times, each successive time the light source being redefined to be another source of irradiated light in the scene that provides the greatest energy output in the scene when the previously defined light source is disregarded, thereby obtaining a plurality of radiosities collectively indicating global illumination of the scene;
and
g) controlling the computer graphics display device to display the three dimensional image of the scene based upon the radiosities determined from step (f).

8 more elements

a) creating a geometric model of a scene to be rendered and storing data representative of said geometric model as a database in the computer, said data including at least the geometry and surface reflectivity of light emitters and objects in the scene;
b) approximating surfaces of each object in the scene as patches in three dimensional space, each patch being approximated as one or more elements defined by vertices;
c) selecting a source of irradiated light in the scene, the selected source of irradiated light being either one of the light emitters or a surface that reflects light emitted by one of the light emitters, the selected source defining a light source comprising a source surface having an area, said source surface comprising a plurality of sample points;
d) performing the following steps for each vertex:
i) determining, for the vertex, individual form factors for each of a selected number of sample points, each individual form factor being determined by ray tracing from the vertex to that sample point, the individual form factor determined for each sample point having a magnitude, said magnitude being zero if, while ray tracing from the vertex to that sample point, the ray intersects an object in the scene before reaching the sample point, the number of sample points for which individual form factors are determined being independently selected from vertex to vertex;
and
ii) summing the individual form factors and dividing by the selected number of sample points to produce a total form factor for the vertex, the total form factor being computed according to a relationship of the form:
##EQU12## where:
F is the total form factor which specifies the fraction of energy leaving the source surface and arriving at the vertex;
n is the number of sample points on the source surface;
i represents one of the n sample points on the source surface (for i=1 to n);
.beta..sub.i controls the magnitude of the individual form factor for sample point i and equals 0 if, while ray tracing from the vertex to sample point i, the ray intersects an object in the scene before reaching the sample point, and equals 1 if the ray does not intersect an object;
.theta..sub.1i is the angle between a surface normal of the source surface at the sample point i and the ray cast from the vertex to the sample point i during ray tracing;
.theta..sub.2i is the angle between the surface normal of the patch at the vertex and the ray cast from the vertex to the sample point i during ray tracing;
r.sub.i is the distance between the sample point i and the vertex;
and
A is the area of the source surface;
e) determining radiosity at each vertex based upon the form factors determined in step (d) for each vertex;
f) repeating steps (c)-(e) a selected number of times, each successive time the light source being redefined to be another source of irradiated light in the scene that provides the greatest energy output in the scene when the previously defined light source is disregarded, thereby obtaining a plurality of radiosities collectively indicating global illumination of the scene;
and
g) controlling the computer graphics display device to display the three dimensional image of the scene based upon the radiosities determined from step (f),
at least one of the light sources being defined according to the relationship:
F=[cos .theta..sub.v ( cos .theta..sub.s).sup.n ]/[a.sub.1 +a.sub.2 r+a.sub.3 r.sup.2 ]
where:
F=the form factor;
.theta..sub.v =the angle between a surface normal at a vertex and a ray cast from the vertex to a point on the light source;
.theta..sub.s =the angle between a surface normal at the point on the light source and a ray cast from the vertex to the point on the light source;
n=a distribution characteristic of the light source;
r=the distance between the light source and a vertex;
and
a.sub.1, a.sub.2 and a.sub.3 =constants representing attenuation behavior of irradiated light.

28 more elements

Dependencies are inferred from the claim text.