HP c3700 - Workstation, Reference Manual, Page: 323 / 486

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gluPickMatrix
Chapter 14
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gluPickMatrix
gluPickMatrix
: define a picking region.
C Specification
void gluPickMatrix(
GLdouble x,
GLdouble y,
GLdouble delX,
GLdouble delY,
GLint *viewport)
Parameters
x, y Specify the center of a picking region in window coordinates.
xdelX, delY Specify the width and height, respectively, of the picking region in
window coordinates.
viewport Specifies the current viewport (as from a glGetIntegerv call).
Description
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 re-render the scene. All
primitives that would have been drawn near the cursor are identified and stored in the
selection buffer.
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.
See Also
glGet,
glLoadIdentity,
glMultMatrix,
glRenderMode,
gluPerspective