gluPickMatrix(3G) OpenGL Reference 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 GLUAUTOLOADMATRIX. If GLUAUTOLOADMATRIX 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 */
Page 1
gluPickMatrix(3G) OpenGL Reference gluPickMatrix(3G)
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
glGet, glLoadIndentity, glMultMatrix, glRenderMode, gluPerspective
Page 2