gluNurbsProperty

gluNurbsProperty

NAME

gluNurbsProperty -- set a NURBS property

C SPECIFICATION

void gluNurbsProperty(GLUnurbsObj *nobj,

GLenum property,

GLfloat value)

PARAMETERS

nobj

Specifies the NURBS object (created with gluNewNurbsRenderer).

property

Specifies the property to be set. Valid values are GLU_AUTO_LOAD_MATRIX, GLU_CULLING, GLU_DISPLAY_MODE, and GLU_SAMPLING_TOLERANCE.

value

Specifies the value to which to set the indicated property.

DESCRIPTION

gluNurbsProperty is used to control properties stored in a NURBS object. These properties affect the way that a NURBS curve is rendered. The legal values for property are as follows:

GLU_AUTO_LOAD_MATRIX

value is a Boolean value. When set to GL_TRUE, the NURBS code downloads the projection matrix, the modelview matrix, and the viewport from the OpenGL server to compute sampling and culling matrices for each NURBS curve that is rendered. Sampling and culling matrices are required to determine the tesselation of a NURBS surface into line segments or polygons and to cull a NURBS surface if it lies outside of the viewport. If this mode is set to GL_FALSE, then the user needs to provide a projection matrix, a modelview matrix, and a viewport for the NURBS renderer to use to construct sampling and culling matrices. This can be done with the gluLoadSamplingMatrices function. The default for this mode is GL_TRUE. Changing this mode from GL_TRUE to GL_FALSE does not affect the sampling and culling matrices until gluLoadSamplingMatrices is called.

GLU_CULLING

value is a Boolean value that, when set to GL_TRUE, indicates that a NURBS curve should be discarded prior to tessellation if its control points lie outside the current viewport. The default is GL_FALSE (because a NURBS curve cannot fall entirely within the convex hull of its control points).

GLU_DISPLAY_MODE

value defines how a NURBS surface should be rendered. value can be set to GLU_FILL, GLU_OUTLINE_POLYGON, or GLU_OUTLINE_PATCH. When set to GLU_FILL, the surface is rendered as a set of polygons. GLU_OUTLINE_POLYGON instructs the NURBS library to draw only the outlines of the polygons created by tessellation. GLU_OUTLINE_PATCH causes just the outlines of patches and trim curves defined by the user to be drawn. The default value is GLU_FILL.

GLU_SAMPLING_TOLERANCE

Specifies the maximum length, in pixels to use when the sampling method is set to GLU_PATH_LENGTH. The NURBS code is conservative when rendering a curve or surface, so the actual length can be somewhat shorter. The default value is 50.0 pixels.