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glClipPlane

Chapter 3

glClipPlane

glClipPlane: specify a plane against which all geometry is clipped.

C Speciﬁcation

void glClipPlane(

GLenum plane,

const GLdouble *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 double-precision ﬂoating-point

values. These values are interpreted as a plane equation.

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 glGetIntegerv with argument

GL_MAX_CLIP_PLANES. All implementations support at least six such clipping planes.

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, equation is transformed by the inverse of the modelview matrix

and stored in the resulting eye coordinates. Subsequent changes to the modelview

matrix have no effect on the stored plane-equation components. If the dot product of the

eye coordinates of a vertex with the stored plane equation components is positive or zero,

the vertex is \f2in\f1 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.

• GL_INVALID_OPERATION is generated if glClipPlane is executed between the

execution of glBegin and the corresponding execution of glEnd.

HP b2600 Reference Guide

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