glFrustum(3gl)

1GLFRUSTUM(3G)                                                    GLFRUSTUM(3G)
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NAME

6       glFrustum - multiply the current matrix by a perspective matrix
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C SPECIFICATION

10       void glFrustum( GLdouble left,
11                       GLdouble right,
12                       GLdouble bottom,
13                       GLdouble top,
14                       GLdouble near_val,
15                       GLdouble far_val )
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PARAMETERS

19       left, right Specify  the  coordinates  for  the left and right vertical
20                   clipping planes.
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22       bottom, top Specify the coordinates for the bottom and  top  horizontal
23                   clipping planes.
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25       near_val, far_val
26                   Specify  the  distances  to the near and far depth clipping
27                   planes.  Both distances must be positive.
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DESCRIPTION

30       glFrustum describes a perspective matrix that  produces  a  perspective
31       projection.   The  current  matrix  (see glMatrixMode) is multiplied by
32       this  matrix  and  the  result  replaces  the  current  matrix,  as  if
33       glMultMatrix were called with the following matrix as its argument:
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37                            ⎡⎣r_2i_ng_eh_at_r−__l_ve_af_lt_      0     A  0⎤⎦
38                                  0     t_2o_np_e−_ab_ro__t_vt_ao_lm_ B  0
39                                  0          0     C  D
40                                  0          0     −1 0
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42                                    A=rr_ii_gg_hh_tt_+−_ll_ee_ff_tt_
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45                                    B=tt_oo_pp_+−_bb_oo_tt_tt_oo_mm_
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48                                 C=−ff_aa_rr____vv_aa_ll_+−_nn_ee_aa_rr____vv_aa_ll_
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51                                 D=−2f_fa_ar_r___v_va_al_l−_nn_ee_aa_rr____vv_aa_ll_
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55       Typically,  the  matrix  mode  is  GL_PROJECTION,  and  (left,  bottom,
56       -near_val) and (right, top,  -near_val) specify the points on the  near
57       clipping  plane  that are mapped to the lower left and upper right cor‐
58       ners of the window, assuming that the eye is  located  at  (0,  0,  0).
59       -far_val  specifies  the  location  of  the  far  clipping plane.  Both
60       near_val and far_val must be positive.
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62       Use glPushMatrix and glPopMatrix to save and restore the current matrix
63       stack.
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NOTES

66       Depth buffer precision is affected by the values specified for near_val
67       and far_val.  The greater the ratio of far_val to near_val is, the less
68       effective  the  depth buffer will be at distinguishing between surfaces
69       that are near each other.  If
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71                                     r=n_fe_aa_rr____vv_aa_ll_
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73       roughly log2(r) bits of depth buffer precision  are  lost.   Because  r
74       approaches  infinity  as  near_val approaches 0, near_val must never be
75       set to 0.
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ERRORS

78       GL_INVALID_VALUE is generated if near_val or far_val is  not  positive,
79       or if left = right, or bottom = top.
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81       GL_INVALID_OPERATION  is generated if glFrustum is executed between the
82       execution of glBegin and the corresponding execution of glEnd.
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ASSOCIATED GETS

85       glGet with argument GL_MATRIX_MODE
86       glGet with argument GL_MODELVIEW_MATRIX
87       glGet with argument GL_PROJECTION_MATRIX
88       glGet with argument GL_TEXTURE_MATRIX
89       glGet with argument GL_COLOR_MATRIX
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