gluPickMatrix function

The gluPickMatrix function defines a picking region.

Syntax


void WINAPI gluPickMatrix(
   GLdouble x,
   GLdouble y,
   GLdouble height,
   GLdouble width,
   GLint    viewport[4]
);

Parameters

x

The x window coordinate of a picking region.

y

The y window coordinate of a picking region.

height

The height of the picking region in window coordinates.

width

The width of the picking region in window coordinates.

viewport

The current viewport (as from a glGetIntegerv call).

Return value

This function does not return a value.

Remarks

The gluPickMatrix function creates a projection matrix you can use to restrict drawing to a small region of the viewport.

  1. Use gluPickMatrix to restrict drawing to a small region around the cursor.
  2. Enter selection mode (with glRenderMode), and then 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 were called with the generated matrix.

  1. Call glLoadIdentity to load an identity matrix onto the perspective matrix stack.
  2. Call gluPickMatrix.
  3. Call a function (such as gluPerspective) to multiply the perspective matrix by the pick matrix.

When using gluPickMatrix to pick Non-Uniform Rational B-Spline (NURBS), be careful to turn off the NURBS property, GLU_AUTO_LOAD_MATRIX. If GLU_AUTO_LOAD_MATRIX is not turned off, any NURBS surface rendered is subdivided differently with the pick matrix from how it was subdivided without the pick matrix.

Examples

When rendering a scene as follows:


glMatrixMode(GL_PROJECTION);  
glLoadIdentity( );  
gluPerspective(. . .);  
glMatrixMode(GL_MODELVIEW);  
/* Draw the scene */

the following code selects a portion of the viewport:


glMatrixMode(GL_PROJECTION);  
glLoadIdentity( );  
gluPickMatrix(x, y, width, height, viewport);  
gluPerspective(. . .);  
glMatrixMode(GL_MODELVIEW);  
/* Draw the scene */

Requirements

Minimum supported client

Windows 2000 Professional [desktop apps only]

Minimum supported server

Windows 2000 Server [desktop apps only]

Header

Glu.h

Library

Glu32.lib

DLL

Glu32.dll

See also

glGetIntegerv
glLoadIdentity
glMultMatrix
glRenderMode
gluPerspective

 

 

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