LibertyBSD_xenocara/xenocara/doc/gl-docs/GLU/pickmatrix.3gl

'\" e
'\"! eqn | mmdoc
'\"macro stdmacro
.ds Vn Version 1.2
.ds Dt 6 March 1997
.ds Re Release 1.2.0
.ds Dp May 02 11:53
.ds Dm 37 pickmatri
.ds Xs 64359 5 pickmatrix.gl
.TH GLUPICKMATRIX 3G
.SH NAME
.B "gluPickMatrix
\- define a picking region

.SH C SPECIFICATION
void \f3gluPickMatrix\fP(
GLdouble \fIx\fP,
.nf
.ta \w'\f3void \fPgluPickMatrix( 'u
	GLdouble \fIy\fP,
	GLdouble \fIdelX\fP,
	GLdouble \fIdelY\fP,
	GLint \fI*viewport\fP )
.fi

.EQ
delim $$
.EN
.SH PARAMETERS
.TP \w'\f2x\fP\ \f2y\fP\ \ 'u 
\f2x\fP, \f2y\fP
Specify the center of a picking region in window coordinates.
.TP
\f2delX\fP, \f2delY\fP
Specify the width and height, respectively, of the picking region in window 
coordinates.
.TP
\f2viewport\fP
Specifies the current viewport (as from a \f3glGetIntegerv\fP call).
.SH DESCRIPTION
\%\f3gluPickMatrix\fP 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 \%\f3gluPickMatrix\fP to
restrict drawing to a small region around the cursor.
Then,
enter selection mode (with \f3glRenderMode\fP) and rerender the scene.
All primitives that would have been drawn near
the cursor are identified and stored in the selection buffer.
.P
The matrix created by \%\f3gluPickMatrix\fP is multiplied by the current matrix just
as if \f3glMultMatrix\fP is called with the generated matrix.
To effectively use the generated pick matrix for picking,
first call \f3glLoadIdentity\fP to load an identity matrix onto the
perspective matrix stack.
Then call \%\f3gluPickMatrix\fP,
and finally, call a command (such as \%\f3gluPerspective\fP)
to multiply the perspective matrix by the pick matrix.
.P
When using \%\f3gluPickMatrix\fP to pick NURBS, be careful to turn off the NURBS 
property
\%\f3GLU_AUTO_LOAD_MATRIX\fP.  If \%\f3GLU_AUTO_LOAD_MATRIX\fP 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.
.bp
.SH EXAMPLE
When rendering a scene as follows:
.sp
.Ex
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(...);
glMatrixMode(GL_MODELVIEW);
/* Draw the scene */
.Ee
.sp
a portion of the viewport can be selected as a pick region like this:
.sp
.Ex
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPickMatrix(x, y, width, height, viewport);
gluPerspective(...);
glMatrixMode(GL_MODELVIEW);
/* Draw the scene */
.Ee
.SH SEE ALSO
\f3glGet(3G)\fP,
\f3glLoadIndentity(3G)\fP, 
\f3glMultMatrix(3G)\fP, 
\f3glRenderMode(3G)\fP,
\%\f3gluPerspective(3G)\fP