1GLUPICKMATRIX(3G)                                            GLUPICKMATRIX(3G)
2
3
4

NAME

6       gluPickMatrix - define a picking region
7
8

C SPECIFICATION

10       void gluPickMatrix( GLdouble x,
11                           GLdouble y,
12                           GLdouble delX,
13                           GLdouble delY,
14                           GLint *viewport )
15
16

PARAMETERS

18       x, y Specify the center of a picking region in window coordinates.
19
20       delX, delY
21            Specify  the width and height, respectively, of the picking region
22            in window coordinates.
23
24       viewport
25            Specifies the current viewport (as from a glGetIntegerv call).
26

DESCRIPTION

28       gluPickMatrix creates a projection matrix that can be used to  restrict
29       drawing to a small region of the viewport.  This is typically useful to
30       determine  what  objects  are  being  drawn  near  the   cursor.    Use
31       gluPickMatrix  to restrict drawing to a small region around the cursor.
32       Then, enter selection mode (with glRenderMode) and rerender the  scene.
33       All  primitives  that would have been drawn near the cursor are identi‐
34       fied and stored in the selection buffer.
35
36       The matrix created by gluPickMatrix is multiplied by the current matrix
37       just as if glMultMatrix is called with the generated matrix.  To effec‐
38       tively use the generated pick matrix for picking, first  call  glLoadI‐
39       dentity  to  load an identity matrix onto the perspective matrix stack.
40       Then  call  gluPickMatrix,  and  finally,  call  a  command  (such   as
41       gluPerspective) to multiply the perspective matrix by the pick matrix.
42
43       When  using  gluPickMatrix  to  pick  NURBS, be careful to turn off the
44       NURBS property GLU_AUTO_LOAD_MATRIX.  If  GLU_AUTO_LOAD_MATRIX  is  not
45       turned  off,  then any NURBS surface rendered is subdivided differently
46       with the pick matrix than the way it was subdivided  without  the  pick
47       matrix.
48

EXAMPLE

50       When rendering a scene as follows:
51
52       glMatrixMode(GL_PROJECTION);   glLoadIdentity();   gluPerspective(...);
53       glMatrixMode(GL_MODELVIEW); /* Draw the scene */
54
55       a portion of the viewport can be selected as a pick region like this:
56
57       glMatrixMode(GL_PROJECTION);  glLoadIdentity();   gluPickMatrix(x,   y,
58       width,  height,  viewport);  gluPerspective(...);  glMatrixMode(GL_MOD‐
59       ELVIEW); /* Draw the scene */
60

SEE ALSO

62       glGet(3G),  glLoadIndentity(3G),  glMultMatrix(3G),   glRenderMode(3G),
63       gluPerspective(3G)
64
65
66
67
68                                                             GLUPICKMATRIX(3G)