gluPickMatrix man page on RedHat
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GLUPICKMATRIX(3G) OpenGL Manual GLUPICKMATRIX(3G)
NAME
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.
delX, 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 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);
glLoadIdentity();
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_MODELVIEW);
/* Draw the scene */
SEE ALSO
gluPerspective(), glGet(), glLoadIdentity(), glMultMatrix(),
glRenderMode()
COPYRIGHT
Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed
under the SGI Free Software B License. For details, see
http://oss.sgi.com/projects/FreeB/.
AUTHORS
opengl.org
opengl.org 03/16/2013 GLUPICKMATRIX(3G)
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