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<STRONG>NAME</STRONG>
<STRONG>gluPickMatrix</STRONG> - define a picking region
<STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>
void <STRONG>gluPickMatrix</STRONG>( GLdouble <EM>x</EM>,
GLdouble <EM>y</EM>,
GLdouble <EM>delX</EM>,
GLdouble <EM>delY</EM>,
GLint *<EM>viewport</EM> )
<STRONG>PARAMETERS</STRONG>
<EM>x</EM>, <EM>y</EM> Specify the center of a picking region in window
coordinates.
<EM>delX</EM>, <EM>delY</EM>
Specify the width and height, respectively, of the
picking region in window coordinates.
<EM>viewport</EM>
Specifies the current viewport (as from a <STRONG>glGetIntegerv</STRONG>
call).
<STRONG>DESCRIPTION</STRONG>
<STRONG>gluPickMatrix</STRONG> 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 <STRONG>gluPickMatrix</STRONG> to restrict
drawing to a small region around the cursor. Then, enter
selection mode (with <STRONG>glRenderMode</STRONG>) 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 <STRONG>gluPickMatrix</STRONG> is multiplied by the
current matrix just as if <STRONG>glMultMatrix</STRONG> is called with the
generated matrix. To effectively use the generated pick
matrix for picking, first call <STRONG>glLoadIdentity</STRONG> to load an
identity matrix onto the perspective matrix stack. Then
call <STRONG>gluPickMatrix</STRONG>, and finally, call a command (such as
<STRONG>gluPerspective</STRONG>) to multiply the perspective matrix by the
pick matrix.
When using <STRONG>gluPickMatrix</STRONG> to pick NURBS, be careful to turn
off the NURBS property <STRONG>GLU_AUTO_LOAD_MATRIX</STRONG>. If
<STRONG>GLU_AUTO_LOAD_MATRIX</STRONG> 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.
<STRONG>EXAMPLE</STRONG>
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 */
<STRONG>SEE</STRONG> <STRONG>ALSO</STRONG>
<STRONG>glGet</STRONG>, <STRONG>glLoadIndentity</STRONG>, <STRONG>glMultMatrix</STRONG>, <STRONG>glRenderMode</STRONG>,
<STRONG>gluPerspective</STRONG>
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