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Table of Contents
gluPickMatrix - define a picking region
void gluPickMatrix(
GLdouble x,
GLdouble y,
GLdouble delX,
GLdouble delY,
GLint *viewport )
eqn not supported
- 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);
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);
glGet(3G)
, glLoadIndentity(3G)
,
glMultMatrix(3G)
, glRenderMode(3G)
, gluPerspective(3G)
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