GLUPICKMATRIX(3G) UNIX Programmer's 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 coor-
dinates.
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 primi-
tives that would have been drawn near the cursor are identi-
fied 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 sur-
face rendered is subdivided differently with the pick matrix
than the way it was subdivided without the pick matrix.
MirBSD #10-current Printed 2021-12-07 1
GLUPICKMATRIX(3G) UNIX Programmer's Manual GLUPICKMATRIX(3G)
EXAMPLE
When rendering a scene as follows:
glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluPerspec-
tive(...); 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); gluPerspec-
tive(...); glMatrixMode(GL_MODELVIEW); /* Draw the scene */
SEE ALSO
glGet(3G), glLoadIndentity(3G), glMultMatrix(3G),
glRenderMode(3G), gluPerspective(3G)
MirBSD #10-current Printed 2021-12-07 2