glClipPlane

王朝百科·作者佚名 2010-03-06

glClipPlane

NAME

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. Up to GL_MAX_CLIP_PLANES planes can be specified, where GL_MAX_CLIP_PLANES is at least six in all implementations. 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 in with respect to that clipping plane. Otherwise, it is out.

Clipping planes are enabled and disabled with glEnable and glDisable, and called with the argument GL_CLIP_PLANEi, where i is the plane number.

By default, all clipping planes are 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 called between a call to glBegin and the corresponding call to glEnd.

ASSOCIATED GETS

glGetClipPlane

glIsEnabled with argument GL_CLIP_PLANEi