The gluPickMatrix function defines a picking region.
void gluPickMatrix(
GLdouble x,
GLdouble y,
GLdouble width,
GLdouble height,
GLint viewport[4]
);
The gluPickMatrix function creates a projection matrix you can use to restrict drawing to a small region of the viewport.
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 were called with the generated 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, any NURBS surface rendered is subdivided differently with the pick matrix from how it was subdivided without the pick matrix.
When rendering a scene as follows:
glMatrixMode(GL_PROJECTION);
glLoadIdentity( );
gluPerspective(. . .);
glMatrixMode(GL_MODELVIEW);
/* Draw the scene */
the following code selects a portion of the viewport:
glMatrixMode(GL_PROJECTION);
glLoadIdentity( );
gluPickMatrix(x, y, width, height, viewport);
gluPerspective(. . .);
glMatrixMode(GL_MODELVIEW);
/* Draw the scene */
Windows NT: Use version 3.5 and later.
Windows: Use Windows 95 and later.
Windows CE: Unsupported.
Header: Declared in glu.h.
Import Library: Link with glu32.lib.
glGetIntegerv, glLoadIdentity, glMultMatrix, glRenderMode, gluPerspective