1991-2006 Silicon Graphics, Inc. gluPickMatrix 3G gluPickMatrix define a picking region void gluPickMatrix GLdouble x GLdouble y GLdouble delX GLdouble delY GLint * viewport 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). 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 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. 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 */ gluPerspective, glGet, glLoadIdentity, glMultMatrix, glRenderMode Copyright 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.