gluPickMatrix: define a picking region.
C Specification |
gluPickMatrix creates a projection matrix that can be used to
restrict drawing to a small region of the viewport. This is typically useful
to determine what objects are being drawn near the cursor. Use
gluPickMatrix to restrict drawing to a small region around the
cursor. Then, enter selection mode (with glRenderMode) and rerender the scene.
All primitives that would have been drawn near the cursor are identified and
stored in the selection buffer.
- x, y
- Specify the center of a picking region in window coordinates.
- delX, delY
- Specify the width and height, respectively, of the picking region in
- Specifies the current viewport (as from a glGetIntegerv call).
The matrix created by gluPickMatrix is multiplied by the current
matrix just as if glMultMatrix is
called with the generated matrix. To effectively use the generated pick
matrix for picking, first call glLoadIdentity to load an identity
matrix onto the perspective matrix stack. Then call gluPickMatrix,
and finally, call a command (such as gluPerspective) to multiply the
perspective matrix by the pick matrix.
When using gluPickMatrix to pick NURBS, be careful to turn off the
NURBS property GLU_AUTO_LOAD_MATRIX. If
GLU_AUTO_LOAD_MATRIX is not turned off, then any NURBS surface
rendered is subdivided differently with the pick matrix than the way it was
subdivided without the pick matrix.