glFrustum — multiply the current matrix by a perspective matrix
void glFrustum( | GLdouble | left, |
GLdouble | right, | |
GLdouble | bottom, | |
GLdouble | top, | |
GLdouble | nearVal, | |
GLdouble | farVal) ; |
left
, right
Specify the coordinates for the left and right vertical clipping planes.
bottom
, top
Specify the coordinates for the bottom and top horizontal clipping planes.
nearVal
, farVal
Specify the distances to the near and far depth clipping planes. Both distances must be positive.
glFrustum
describes a perspective matrix that produces a perspective projection.
The current matrix (see glMatrixMode) is multiplied by this matrix
and the result replaces the current matrix, as if
glMultMatrix were called with the following matrix
as its argument:
Typically, the matrix mode is GL_PROJECTION
, and
nearVal
and farVal
must be positive.
Use glPushMatrix and glPopMatrix to save and restore the current matrix stack.
Depth buffer precision is affected by the values specified for
nearVal
and farVal
.
The greater the ratio of farVal
to nearVal
is,
the less effective the depth buffer will be at distinguishing between
surfaces that are near each other.
If
roughly
nearVal
approaches 0,
nearVal
must never be set to 0.
GL_INVALID_VALUE
is generated if nearVal
or farVal
is not
positive, or if left
= right
, or bottom
= top
,
or near
= far
.
GL_INVALID_OPERATION
is generated if glFrustum
is executed between the execution of glBegin
and the corresponding execution of glEnd.
glGet with argument GL_MATRIX_MODE
glGet with argument GL_MODELVIEW_MATRIX
glGet with argument GL_PROJECTION_MATRIX
glGet with argument GL_TEXTURE_MATRIX
glGet with argument GL_COLOR_MATRIX
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