Glu.PickMatrix (gb.opengl.glu)
Static Sub PickMatrix ( X As Float, Y As Float, DelX As Float, DelY As Float, Viewport As Integer[] )
Define a picking region.
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 Gl.GetIntegerv call).
Description
Glu.PickMatrix 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
Glu.PickMatrix to
restrict drawing to a small region around the cursor.
Then,
enter selection mode (with
Gl.RenderMode) 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
Glu.PickMatrix is multiplied by the current matrix just
as if Gl.MultMatrix is called with the generated matrix.
To effectively use the generated pick matrix for picking,
first call
Gl.LoadIdentity to load an identity matrix onto the
perspective matrix stack.
Then call
Glu.PickMatrix,
and, finally, call a command (such as
Glu.Perspective)
to multiply the perspective matrix by the pick matrix.
When using
Glu.PickMatrix 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
See original documentation on OpenGL website