glupickmatrix(3g) [osx man page]

GLUPICKMATRIX(3G)														 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 iden-
       tified 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 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 */

       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

																 GLUPICKMATRIX(3G)

Check Out this Related Man Page

GLUPERSPECTIVE(3G)														GLUPERSPECTIVE(3G)

NAME

       gluPerspective - set up a perspective projection matrix

C SPECIFICATION

       void gluPerspective( GLdouble fovy,
			    GLdouble aspect,
			    GLdouble zNear,
			    GLdouble zFar )

PARAMETERS

       fovy    Specifies the field of view angle, in degrees, in the y direction.

       aspect  Specifies  the  aspect ratio that determines the field of view in the x direction.  The aspect ratio is the ratio of x (width) to y
	       (height).

       zNear   Specifies the distance from the viewer to the near clipping plane (always positive).

       zFar    Specifies the distance from the viewer to the far clipping plane (always positive).

DESCRIPTION

       gluPerspective specifies a viewing frustum into the world coordinate system.  In general, the aspect ratio in gluPerspective  should  match
       the  aspect  ratio of the associated viewport. For example, aspect = 2.0 means the viewer's angle of view is twice as wide in x as it is in
       y.  If the viewport is twice as wide as it is tall, it displays the image without distortion.

       The matrix generated by gluPerspective is multipled by the current matrix, just as if glMultMatrix were called with the	generated  matrix.
       To load the perspective matrix onto the current matrix stack instead, precede the call to gluPerspective with a call to glLoadIdentity.

       Given f defined as follows:

								 f  = cotangent(fovy/2)

       The generated matrix is
	     f
	------------	   0		  0		 0
	   aspect

	    0		   f		  0		 0

				      zFar+zNear    2*zFar*zNear
	    0		   0	      ----------    ------------
				      zNear-zFar     zNear-zFar

	    0		   0		  -1		 0

NOTES

       Depth  buffer precision is affected by the values specified for zNear and zFar.	The greater the ratio of zFar to zNear is, the less effec-
       tive the depth buffer will be at distinguishing between surfaces that are near each other.  If

								     r = zFar/zNear

       roughly log2(r) bits of depth buffer precision are lost.  Because r approaches infinity as zNear approaches 0, zNear must never be  set	to
       0.

SEE ALSO

       glFrustum, glLoadIdentity, glMultMatrix, gluOrtho2D

																GLUPERSPECTIVE(3G)

Linux and UNIX Man Pages

glupickmatrix(3g) [osx man page]

Check Out this Related Man Page