NAME

DoGlbRendMaxObjs − Create a studio attribute object that defines the maximum number of objects per spatial subdivision for global ray tracing

SYNOPSIS

C:

DtObject DoGlbRendMaxObjs(maxobjs)
DtInt maxobjs;

FORTRAN:

INTEGER∗4 DOGRMO(MAXOBJ)
INTEGER∗4 MAXOBJ

DESCRIPTION

DoGlbRendMaxObjs creates a studio attribute object that defines the maximum number of objects per spatial subdivision for global ray tracing.  The parameter maxobjs specifies the maximum number of geometric entities allowed per spatial subdivision prior to ray tracing. 

DoGlbRendMaxObjs affects only renderers that use ray tracing.  The rendering style is set with DvSetRendStyle <DVSRS>. 

Ray tracing is the process of determining which objects in the scene are in the path of an arbitrary vector (ray) in space.  Ray casting is used in the generation of global shading effects like shadows, object-to-object reflections, and transparency. 

Many renderers use a ray tracing algorithm based on spatial subdivisions to facilitate the ray tracing process in complex scenes containing many geometric entities.  A preprocessing step is performed on the scene to collect information about all geometric entities in the environment and then to perform a regular binary subdivision of all space containing geometric entities. 

The subdivision creates a three-dimensional grid of boxes; i.e, the first level subdivision creates 8 equal boxes placed 2 wide by 2 high by 2 deep.  The second level subdivision, if fully subdivided, creates 64 boxes, and so on.  Each box can contain 0 or more geometric entities with more boxes wherever the density of geometric entities is higher. 

In Doré, the amount of spatial subdivision performed is controlled by these factors (the latter two factors have user-defined control):

The number, density, and distribution of geometric entities in the scene. 

The maximum number of geometric entries allowed per spatial subdivision, using DoGlbRendMaxObjs. 

The maximum number of subdivisions allowed, using DoGlbRendMaxSub <DOGRMS>. 

DoGlbRendMaxObjs determines the maximum number of geometric entities that a box may contain without being further subdivided.  For example, if the maximum number is set to 2, then boxes containing 2 and fewer entities will not be subdivided further; boxes containing more than 2 will be subdivided.  Often a given area of space will always contain more than the maximum number of geometric entities; i.e., if 5 geometric entities intersect at a given point, then the area of space containing that point will never contain less than 5 geometric entities. 

DoGlbRendMaxSub <DOGRMS> indicates how many levels to subdivide before subdivision of that branch is terminated; i.e., it indicates when to stop subdividing regardless of the number of geometric entities per box. 

DEFAULTS

The default value for DoGlbRendMaxObjs is 1. 

SEE ALSO

DoGlbRendMaxSub(3D), DoGlbRendRayLevel(3D)
 

September 02, 1992