| Extracted from Pike v7.8 release 866 at 2016-04-05.

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GL

# Method GL.glFrustum()

Method glFrustum

  `void glFrustum(float left, float right, float bottom, float top, float zNear, float zFar)`

Description

  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:

  .sp 5 .ce .EQ down 130 {left ( ~~ matrix { ccol { {{2 ~ "zNear"} over {"right" - "left"}} above 0 above 0 above 0 } ccol { 0 above {{2 ~ "zNear"} over {"top" - "bottom"}} ~ above 0 above 0 } ccol { A ~~~~ above B ~~~~ above C ~~~~ above -1 ~~~~} ccol { 0 above 0 above D above 0} } ~~~ right )} .EN .sp .ce .EQ down 130 {A ~=~ {"right" + "left"} over {"right" - "left"}} .EN .sp .ce .EQ down 130 {B ~=~ {"top" + "bottom"} over {"top" - "bottom"}} .EN .sp .ce .EQ down 130 {C ~=~ -{{"zFar" + "zNear"} over {"zFar" - "zNear"}}} .EN .sp .ce .EQ down 130 {D ~=~ -{{2 ~ "zFar" ~ "zNear"} over {"zFar" - "zNear"}}} .EN .sp

  Typically, the matrix mode is GL_PROJECTION , and (left, bottom, -zNear) and (right, top, -zNear) 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). -zFar specifies the location of the far clipping plane. Both zNear and zFar must be positive.

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

Parameter `left`

  Specify the coordinates for the left and right vertical clipping planes.

Parameter `bottom`

  Specify the coordinates for the bottom and top horizontal clipping planes.

Parameter `zNear`

  Specify the distances to the near and far depth clipping planes. Both distances must be positive.

Throws

  GL_INVALID_VALUE is generated if zNear or zFar is not positive.

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