MirBSD manpage: glFrustum(3)

GLFRUSTUM(3G)       UNIX Programmer's Manual        GLFRUSTUM(3G)


     glFrustum - multiply the current matrix by a perspective


     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 posi-


     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:

            |   ____e__r___a___
            |   right - left        0
            |                                            |
            |        0        ____e__r___a___   A           |
            |        0        top - bottom               |
            |        0              0        B       0   |
                                    0        C           |
                                             -1      0   |
                                                     D   |
                                                     0   |
                           A = t_o_p__t±_b__l_t_o_m_
                       C = -2__r_a_r___v__-__n_e_a_r___v_a_l_
                       D = -far_val - near_val

MirBSD #10-current     Printed 2021-12-07                       1

GLFRUSTUM(3G)       UNIX Programmer's Manual        GLFRUSTUM(3G)

     Typically, the matrix mode is GL_PROJECTION, and (left, bot-
     tom, -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.
                             r = near_val
     roughly log2(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 exe-
     cution 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)

MirBSD #10-current     Printed 2021-12-07                       2

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