Name

glClipPlane — specify a plane against which all geometry is clipped

C Specification

void glClipPlanef(GLenum plane,
 const GLfloat *equation);
 
void glClipPlanex(GLenum plane,
 const GLfixed *equation);
 

Parameters

plane

Specifies which clipping plane is being positioned. Symbolic names of the form GL_CLIP_PLANEi, where i is an integer between 0 and GL_MAX_CLIP_PLANES -1 , are accepted.

equation

Specifies the address of an array of four fixed-point or floating-point values. These are the coefficients of a plane equation in object coordinates: p1, p2, p3, and p4, in that order.

Description

Geometry is always clipped against the boundaries of a six-plane frustum in x, y, and z. glClipPlane allows the specification of additional planes, not necessarily perpendicular to the x, y, or z axis, against which all geometry is clipped. To determine the maximum number of additional clipping planes, call glGet with argument GL_MAX_CLIP_PLANES. All implementations support at least one such clipping plane. Because the resulting clipping region is the intersection of the defined half-spaces, it is always convex.

glClipPlane specifies a half-space using a four-component plane equation. When glClipPlane is called, the coefficients given by equation are transformed by the inverse of the modelview matrix and stored in the resulting eye coordinates. The resulting plane equation is undefined, if the model-view matrix M is singular and it may be inaccurate, if M is poorly conditioned. Subsequent changes to the modelview matrix have no effect on the stored plane-equation coefficients. If the dot product of the eye coordinates of a vertex with the stored plane equation components is positive or zero, the vertex is in with respect to that clipping plane. Otherwise, it is out.

To enable and disable clipping planes, call glEnable and glDisable with the argument GL_CLIP_PLANEi, where i is the plane number.

All clipping planes are initially defined as (0, 0, 0, 0) in eye coordinates and are disabled.

Notes

It is always the case that GL_CLIP_PLANEi = GL_CLIP_PLANE0 + i .

Errors

GL_INVALID_ENUM is generated if plane is not an accepted value.

Associated Gets

glGetClipPlane, glIsEnabled with argument GL_CLIP_PLANEi.

See Also

glGetClipPlane, glGet, glEnable

Copyright

Copyright © 2003-2004 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.