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Manual Reference Pages  - GLFRUSTUM (3G)

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glFrustum - multiply the current matrix by a perspective matrix

CONTENTS

C Specification
Parameters
Description
Notes
Errors
Associated Gets
See Also

void glFrustum( GLdouble left,

              GLdouble right,
              GLdouble bottom,
              GLdouble top,
              GLdouble near_val,
              GLdouble far_val )

left, right	Specify the coordinates for the left and right vertical clipping planes.
bottom, top	Specify the coordinates for the bottom and top horizontal clipping planes.
near_val, far_val	Specify the distances to the near and far depth clipping planes. Both distances must be positive.

 glFrustum describes a perspective matrix that produces a perspective projection. The current matrix (see  glMatrixMode) is multiplied by this matrix and the result replaces the current matrix, as if  glMultMatrix were called with the following matrix as its argument:

down150[ down165matrix ( 2 near_val / right - left 0 0 0 0 2 near_val / top - bottom 0 0 A B C -1 0 0 D 0 ) ]

down130A = right + left / right - left

down130B = top + bottom / top - bottom

down130C = -far_val + near_val / far_val - near_val

down130D = - 2 far_val near_val / far_val - near_val

Typically, the matrix mode is  GL_PROJECTION, and (left, bottom, -near_val) and (right, top, -near_val) specify the points on the near clipping plane that are mapped to the lower left and upper right corners of the window, assuming that the eye is located at (0, 0, 0). -far_val specifies the location of the far clipping plane. Both near_val and far_val must be positive.

Use  glPushMatrix and  glPopMatrix to save and restore the current matrix stack.

Depth buffer precision is affected by the values specified for near_val and far_val. The greater the ratio of far_val to near_val is, the less effective the depth buffer will be at distinguishing between surfaces that are near each other. If

r = far_val / near_val

roughly log ₂(r) bits of depth buffer precision are lost. Because r approaches infinity as near_val approaches 0, near_val must never be set to 0.

 GL_INVALID_VALUE is generated if near_val or far_val is not positive, or if left = right, or bottom = top.

 GL_INVALID_OPERATION is generated if  glFrustum is executed between the execution of  glBegin and the corresponding execution of  glEnd.

 glGet with argument  GL_MATRIX_MODE
 glGet with argument  GL_MODELVIEW_MATRIX
 glGet with argument  GL_PROJECTION_MATRIX
 glGet with argument  GL_TEXTURE_MATRIX
 glGet with argument  GL_COLOR_MATRIX

 glOrtho(3G),  glMatrixMode(3G),  glMultMatrix(3G),  glPushMatrix(3G),  glViewport(3G)

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