glClipPlane

The glClipPlane function specifies a plane against which all geometry is clipped.

void glClipPlane(
  GLenum plane,  const GLdouble *equation);

Parameters

• plane
  The clipping plane that 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
  The address of an array of four double-precision floating-point values. These values are interpreted as a plane equation.

Remarks

Geometry is always clipped against the boundaries of a six-plane frustum in x, y, and z. The glClipPlane function 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.

The glClipPlane function specifies a half-space using a four-component plane equation. When you call glClipPlane, 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.

Use the glEnable and glDisable functions to enable and disable clipping planes. Call clipping planes 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.

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

The following functions retrieve information related to glClipPlane:

glGetClipPlane

glIsEnabled with argument GL_CLIP_PLANEi

Error Codes

The following are the error codes generated and their conditions.

Requirements

**  Windows NT/2000:** Requires Windows NT 3.5 or later.
**  Windows 95/98:** Requires Windows 95 or later. Available as a redistributable for Windows 95.
**  Header:** Declared in Gl.h.
**  Library:** Use Opengl32.lib.

See Also

glBegin, glDisable, glEnable, glEnd, glGetClipPlane, glIsEnabled