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GLUPICKMATRIX() GLUPICKMATRIX() NAME gluPickMatrix - define a picking region C SPECIFICATION void gluPickMatrix( GLdouble x, GLdouble y, GLdouble delX, GLdouble delY, GLint *viewport ) delim $$ 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 gluPickMa- trix 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 effec- tively use the generated pick matrix for picking, first call glLoadI- dentity to load an identity matrix onto the perspective matrix stack. Then call gluPickMatrix, and finally, call a command (such as gluPer- spective) 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_MOD- ELVIEW); /* Draw the scene */ SEE ALSO glGet, glLoadIndentity, glMultMatrix, glRenderMode, gluPerspective GLUPICKMATRIX()
NAME | C SPECIFICATION | PARAMETERS | DESCRIPTION | EXAMPLE | SEE ALSO
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