gluPickMatrix()gluPickMatrix()NAMEgluPickMatrix - define a picking region
SYNOPSIS
void gluPickMatrix(
GLdouble x,
GLdouble y,
GLdouble delX,
GLdouble delY,
GLint *viewport );
PARAMETERS
Specify the center of a picking region in window coordinates. Specify
the width and height, respectively, of the picking region in window
coordinates. Specifies the current viewport (as from a glGetIntegerv()
call).
DESCRIPTIONgluPickMatrix() 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 cur‐
sor. 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.
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.
EXAMPLE
When rendering a scene as follows: glMatrixMode(GL_PROJECTION); glLoad‐
Identity(); gluPerspective(...); glMatrixMode(GL_MODELVIEW); /* Draw
the scene */
a portion of the viewport can be selected as a pick region like this:
glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluPickMatrix(x, y,
width, height, viewport); gluPerspective(...); glMatrixMode(GL_MOD‐
ELVIEW); /* Draw the scene */
SEE ALSOglGet(3), glLoadIndentity(3), glMultMatrix(3), glRenderMode(3), gluPer‐
spective(3)gluPickMatrix()