Glu.PickMatrix (gb.opengl.glu)

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