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Text File  |  2002-10-03  |  7.9 KB  |  163 lines
  1.  
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  4. ffffggggllllFFFFrrrruuuussssttttuuuummmm((((3333GGGG))))                 OOOOppppeeeennnnGGGGLLLL RRRReeeeffffeeeerrrreeeennnncccceeee                 ffffggggllllFFFFrrrruuuussssttttuuuummmm((((3333GGGG))))
  5.  
  6.  
  7.  
  8. NNNNAAAAMMMMEEEE
  9.      ffffggggllllFFFFrrrruuuussssttttuuuummmm - multiply the current matrix by a perspective matrix
  10.  
  11.  
  12. FFFFOOOORRRRTTTTRRRRAAAANNNN SSSSPPPPEEEECCCCIIIIFFFFIIIICCCCAAAATTTTIIIIOOOONNNN
  13.      SUBROUTINE ffffggggllllFFFFrrrruuuussssttttuuuummmm( REAL*4 _l_e_f_t,
  14.                             REAL*4 _r_i_g_h_t,
  15.                             REAL*4 _b_o_t_t_o_m,
  16.                             REAL*4 _t_o_p,
  17.                             REAL*4 _n_e_a_r,
  18.                             REAL*4 _f_a_r )
  19.  
  20.  
  21. PPPPAAAARRRRAAAAMMMMEEEETTTTEEEERRRRSSSS
  22.      _l_e_f_t, _r_i_g_h_t Specify the coordinates for the left and right vertical
  23.                  clipping planes.
  24.  
  25.      _b_o_t_t_o_m, _t_o_p Specify the coordinates for the bottom and top horizontal
  26.                  clipping planes.
  27.  
  28.      _n_e_a_r, _f_a_r   Specify the distances to the near and far depth clipping
  29.                  planes.  Both distances must be positive.
  30.  
  31. DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
  32.      ffffggggllllFFFFrrrruuuussssttttuuuummmm describes a perspective matrix that produces a perspective
  33.      projection.  The current matrix (see ffffggggllllMMMMaaaattttrrrriiiixxxxMMMMooooddddeeee) is multiplied by this
  34.      matrix and the result replaces the current matrix, as if ffffggggllllMMMMuuuullllttttMMMMaaaattttrrrriiiixxxx
  35.      were called with the following matrix as its argument:
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  41.                   |                                             |
  42.  
  43.                   |                                             |
  44.  
  45.                   |                                             |
  46.  
  47.                   |                2 near____________                             |
  48.                                                 0         A        0
  49.                   |          right - left                             |
  50.  
  51.                   |                                             |
  52.                                                 2 near____________
  53.                   |          0                        B        0   |
  54.                                            top - bottom
  55.                   |                                             |
  56.  
  57.                   |          0               0          C        D   |
  58.  
  59.                   |                                            |
  60.                            0              0        -1       0
  61.  
  62.  
  63.                                                  right + left____________
  64.                                  A =
  65.                                      right - left
  66.  
  67.  
  68.                                                  top + bottom____________
  69.                                  B =
  70.                                      top - bottom
  71.  
  72.  
  73.                                                  far + near__________
  74.                                   C = -
  75.                                        far - near
  76.  
  77.  
  78.                                                  2 far near__________
  79.                                   D = -
  80.                                        far - near
  81.  
  82.  
  83.      Typically, the matrix mode is GGGGLLLL____PPPPRRRROOOOJJJJEEEECCCCTTTTIIIIOOOONNNN, and (_l_e_f_t, _b_o_t_t_o_m, -_n_e_a_r)
  84.      and (_r_i_g_h_t, _t_o_p,  -_n_e_a_r) specify the points on the near clipping plane
  85.      that are mapped to the lower left and upper right corners of the window,
  86.  
  87.  
  88.  
  89.                                                                         PPPPaaaaggggeeee 1111
  90.  
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  96. ffffggggllllFFFFrrrruuuussssttttuuuummmm((((3333GGGG))))                 OOOOppppeeeennnnGGGGLLLL RRRReeeeffffeeeerrrreeeennnncccceeee                 ffffggggllllFFFFrrrruuuussssttttuuuummmm((((3333GGGG))))
  97.  
  98.  
  99.  
  100.      assuming that the eye is located at (0, 0, 0).  -_f_a_r specifies the
  101.      location of the far clipping plane.  Both _n_e_a_r and _f_a_r must be positive.
  102.  
  103.      Use ffffggggllllPPPPuuuusssshhhhMMMMaaaattttrrrriiiixxxx and ffffggggllllPPPPooooppppMMMMaaaattttrrrriiiixxxx to save and restore the current matrix
  104.      stack.
  105.  
  106. NNNNOOOOTTTTEEEESSSS
  107.      Depth buffer precision is affected by the values specified for _n_e_a_r and
  108.      _f_a_r.  The greater the ratio of _f_a_r to _n_e_a_r is, the less effective the
  109.      depth buffer will be at distinguishing between surfaces that are near
  110.      each other.  If
  111.  
  112.                                              far____
  113.                                      r =
  114.                                          near
  115.  
  116.  
  117.      roughly log (r) bits of depth buffer precision are lost.  Because r
  118.                 2
  119.      approaches infinity as _n_e_a_r approaches 0, _n_e_a_r must never be set to 0.
  120.  
  121. EEEERRRRRRRROOOORRRRSSSS
  122.      GGGGLLLL____IIIINNNNVVVVAAAALLLLIIIIDDDD____VVVVAAAALLLLUUUUEEEE is generated if _n_e_a_r or _f_a_r is not positive, or if _l_e_f_t
  123.      = _r_i_g_h_t, or _b_o_t_t_o_m = _t_o_p.
  124.  
  125.      GGGGLLLL____IIIINNNNVVVVAAAALLLLIIIIDDDD____OOOOPPPPEEEERRRRAAAATTTTIIIIOOOONNNN is generated if ffffggggllllFFFFrrrruuuussssttttuuuummmm is executed between the
  126.      execution of ffffggggllllBBBBeeeeggggiiiinnnn and the corresponding execution of ffffggggllllEEEEnnnndddd.
  127.  
  128. AAAASSSSSSSSOOOOCCCCIIIIAAAATTTTEEEEDDDD GGGGEEEETTTTSSSS
  129.      ffffggggllllGGGGeeeetttt with argument GGGGLLLL____MMMMAAAATTTTRRRRIIIIXXXX____MMMMOOOODDDDEEEE
  130.      ffffggggllllGGGGeeeetttt with argument GGGGLLLL____MMMMOOOODDDDEEEELLLLVVVVIIIIEEEEWWWW____MMMMAAAATTTTRRRRIIIIXXXX
  131.      ffffggggllllGGGGeeeetttt with argument GGGGLLLL____PPPPRRRROOOOJJJJEEEECCCCTTTTIIIIOOOONNNN____MMMMAAAATTTTRRRRIIIIXXXX
  132.      ffffggggllllGGGGeeeetttt with argument GGGGLLLL____TTTTEEEEXXXXTTTTUUUURRRREEEE____MMMMAAAATTTTRRRRIIIIXXXX
  133.      ffffggggllllGGGGeeeetttt with argument GGGGLLLL____CCCCOOOOLLLLOOOORRRR____MMMMAAAATTTTRRRRIIIIXXXX
  134.  
  135.  
  136. SSSSEEEEEEEE AAAALLLLSSSSOOOO
  137.      ffffggggllllOOOOrrrrtttthhhhoooo, ffffggggllllMMMMaaaattttrrrriiiixxxxMMMMooooddddeeee, ffffggggllllMMMMuuuullllttttMMMMaaaattttrrrriiiixxxx, ffffggggllllPPPPuuuusssshhhhMMMMaaaattttrrrriiiixxxx, ffffggggllllVVVViiiieeeewwwwppppoooorrrrtttt
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  159.                                                                         PPPPaaaaggggeeee 2222
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