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Text File  |  2002-10-03  |  19.6 KB  |  301 lines
  1.  
  2.  
  3.  
  4. ggggllllBBBBlllleeeennnnddddFFFFuuuunnnncccc((((3333GGGG))))                OOOOppppeeeennnnGGGGLLLL RRRReeeeffffeeeerrrreeeennnncccceeee                ggggllllBBBBlllleeeennnnddddFFFFuuuunnnncccc((((3333GGGG))))
  5.  
  6.  
  7.  
  8. NNNNAAAAMMMMEEEE
  9.      ggggllllBBBBlllleeeennnnddddFFFFuuuunnnncccc - specify pixel arithmetic
  10.  
  11.  
  12. CCCC SSSSPPPPEEEECCCCIIIIFFFFIIIICCCCAAAATTTTIIIIOOOONNNN
  13.      void ggggllllBBBBlllleeeennnnddddFFFFuuuunnnncccc( GLenum _s_f_a_c_t_o_r,
  14.                        GLenum _d_f_a_c_t_o_r )
  15.  
  16.  
  17. PPPPAAAARRRRAAAAMMMMEEEETTTTEEEERRRRSSSS
  18.      _s_f_a_c_t_o_r  Specifies how the red, green, blue, and alpha source blending
  19.               factors are computed.  The following symbolic constants are
  20.               accepted:  GGGGLLLL____ZZZZEEEERRRROOOO, GGGGLLLL____OOOONNNNEEEE, GGGGLLLL____DDDDSSSSTTTT____CCCCOOOOLLLLOOOORRRR,
  21.               GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____DDDDSSSSTTTT____CCCCOOOOLLLLOOOORRRR, GGGGLLLL____SSSSRRRRCCCC____AAAALLLLPPPPHHHHAAAA, GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____SSSSRRRRCCCC____AAAALLLLPPPPHHHHAAAA,
  22.               GGGGLLLL____DDDDSSSSTTTT____AAAALLLLPPPPHHHHAAAA, GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____DDDDSSSSTTTT____AAAALLLLPPPPHHHHAAAA, and GGGGLLLL____SSSSRRRRCCCC____AAAALLLLPPPPHHHHAAAA____SSSSAAAATTTTUUUURRRRAAAATTTTEEEE.
  23.               The initial value is GGGGLLLL____OOOONNNNEEEE.
  24.  
  25.               Additionally, if the GGGGLLLL____AAAARRRRBBBB____iiiimmmmaaaaggggiiiinnnngggg extension is supported, the
  26.               following constants are accepted:  GGGGLLLL____CCCCOOOONNNNSSSSTTTTAAAANNNNTTTT____CCCCOOOOLLLLOOOORRRR,
  27.               GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____CCCCOOOONNNNSSSSTTTTAAAANNNNTTTT____CCCCOOOOLLLLOOOORRRR, GGGGLLLL____CCCCOOOONNNNSSSSTTTTAAAANNNNTTTT____AAAALLLLPPPPHHHHAAAA,
  28.               GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____CCCCOOOONNNNSSSSTTTTAAAANNNNTTTT____AAAALLLLPPPPHHHHAAAA.
  29.  
  30.      _d_f_a_c_t_o_r  Specifies how the red, green, blue, and alpha destination
  31.               blending factors are computed.  Eight symbolic constants are
  32.               accepted:  GGGGLLLL____ZZZZEEEERRRROOOO, GGGGLLLL____OOOONNNNEEEE, GGGGLLLL____SSSSRRRRCCCC____CCCCOOOOLLLLOOOORRRR,
  33.               GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____SSSSRRRRCCCC____CCCCOOOOLLLLOOOORRRR, GGGGLLLL____SSSSRRRRCCCC____AAAALLLLPPPPHHHHAAAA, GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____SSSSRRRRCCCC____AAAALLLLPPPPHHHHAAAA,
  34.               GGGGLLLL____DDDDSSSSTTTT____AAAALLLLPPPPHHHHAAAA, and GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____DDDDSSSSTTTT____AAAALLLLPPPPHHHHAAAA.  The initial value is
  35.               GGGGLLLL____ZZZZEEEERRRROOOO.
  36.  
  37.               Additionally, if the GGGGLLLL____AAAARRRRBBBB____iiiimmmmaaaaggggiiiinnnngggg extension is supported, the
  38.               following constants are accepted:  GGGGLLLL____CCCCOOOONNNNSSSSTTTTAAAANNNNTTTT____CCCCOOOOLLLLOOOORRRR,
  39.               GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____CCCCOOOONNNNSSSSTTTTAAAANNNNTTTT____CCCCOOOOLLLLOOOORRRR, GGGGLLLL____CCCCOOOONNNNSSSSTTTTAAAANNNNTTTT____AAAALLLLPPPPHHHHAAAA,
  40.               GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____CCCCOOOONNNNSSSSTTTTAAAANNNNTTTT____AAAALLLLPPPPHHHHAAAA.
  41.  
  42. DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
  43.      In RGBA mode, pixels can be drawn using a function that blends the
  44.      incoming (source) RGBA values with the RGBA values that are already in
  45.      the frame buffer (the destination values).  Blending is initially
  46.      disabled.  Use ggggllllEEEEnnnnaaaabbbblllleeee and ggggllllDDDDiiiissssaaaabbbblllleeee with argument GGGGLLLL____BBBBLLLLEEEENNNNDDDD to enable
  47.      and disable blending.
  48.  
  49.      ggggllllBBBBlllleeeennnnddddFFFFuuuunnnncccc defines the operation of blending when it is enabled.
  50.      _s_f_a_c_t_o_r specifies which of nine methods is used to scale the source color
  51.      components.  _d_f_a_c_t_o_r specifies which of eight methods is used to scale
  52.      the destination color components.  The eleven possible methods are
  53.      described in the following table.  Each method defines four scale
  54.      factors, one each for red, green, blue, and alpha.
  55.  
  56.      In the table and in subsequent equations, source and destination color
  57.      components are referred to as (R ,G ,B ,A ) and (R ,G ,B ,A ).  The color
  58.                                      s  s  s  s        d  d  d  d
  59.      specified by ggggllllBBBBlllleeeennnnddddCCCCoooolllloooorrrr is referred to as (R ,G ,B ,A ).  They are
  60.                                                    c  c  c  c
  61.      understood to have integer values between 0 and (k ,k ,k ,k ), where
  62.                                                        R  G  B  A
  63.  
  64.  
  65.  
  66.                                                                         PPPPaaaaggggeeee 1111
  67.  
  68.  
  69.  
  70.  
  71.  
  72.  
  73. ggggllllBBBBlllleeeennnnddddFFFFuuuunnnncccc((((3333GGGG))))                OOOOppppeeeennnnGGGGLLLL RRRReeeeffffeeeerrrreeeennnncccceeee                ggggllllBBBBlllleeeennnnddddFFFFuuuunnnncccc((((3333GGGG))))
  74.  
  75.  
  76.  
  77.                                             m
  78.                                              c
  79.                                       k  = 2  -1
  80.                                        c
  81.  
  82.      and (m ,m ,m ,m ) is the number of red, green, blue, and alpha bitplanes.
  83.            R  G  B  A
  84.  
  85.      Source and destination scale factors are referred to as (s ,s ,s ,s ) and
  86.                                                                R  G  B  A
  87.      (d ,d ,d ,d ).  The scale factors described in the table, denoted
  88.        R  G  B  A
  89.      (f ,f ,f ,f ), represent either source or destination factors.  All scale
  90.        R  G  B  A
  91.      factors have range [0, 1].
  92.  
  93.      _________________________________________________________________________
  94.      PPPPaaaarrrraaaammmmeeeetttteeeerrrr                                (f ,  f ,  f ,  f )
  95.                                                 R    G    B    A
  96.      _________________________________________________________________________
  97.      GGGGLLLL____ZZZZEEEERRRROOOO                                      (0, 0, 0, 0)
  98.      GGGGLLLL____OOOONNNNEEEE                                       (1, 1, 1, 1)
  99.      GGGGLLLL____SSSSRRRRCCCC____CCCCOOOOLLLLOOOORRRR                         (R /k , G /k , B /k , A /k )
  100.                                             s  R   s  G   s  B   s  A
  101.      GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____SSSSRRRRCCCC____CCCCOOOOLLLLOOOORRRR        (1, 1, 1, 1) - (R /k , G /k , B /k , A /k )
  102.                                                     s  R   s  G   s  B   s  A
  103.      GGGGLLLL____DDDDSSSSTTTT____CCCCOOOOLLLLOOOORRRR                         (R /k , G /k , B /k , A /k )
  104.                                             d  R   d  G   d  B   d  A
  105.      GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____DDDDSSSSTTTT____CCCCOOOOLLLLOOOORRRR        (1, 1, 1, 1) - (R /k , G /k , B /k , A /k )
  106.                                                     d  R   d  G   d  B   d  A
  107.      GGGGLLLL____SSSSRRRRCCCC____AAAALLLLPPPPHHHHAAAA                         (A /k , A /k , A /k , A /k )
  108.                                             s  A   s  A   s  A   s  A
  109.      GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____SSSSRRRRCCCC____AAAALLLLPPPPHHHHAAAA        (1, 1, 1, 1) - (A /k , A /k , A /k , A /k )
  110.                                                     s  A   s  A   s  A   s  A
  111.      GGGGLLLL____DDDDSSSSTTTT____AAAALLLLPPPPHHHHAAAA                         (A /k , A /k , A /k , A /k )
  112.                                             d  A   d  A   d  A   d  A
  113.      GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____DDDDSSSSTTTT____AAAALLLLPPPPHHHHAAAA        (1, 1, 1, 1) - (A /k , A /k , A /k , A /k )
  114.                                                     d  A   d  A   d  A   d  A
  115.      GGGGLLLL____SSSSRRRRCCCC____AAAALLLLPPPPHHHHAAAA____SSSSAAAATTTTUUUURRRRAAAATTTTEEEE                        (i, i, i, 1)
  116.      GGGGLLLL____CCCCOOOONNNNSSSSTTTTAAAANNNNTTTT____CCCCOOOOLLLLOOOORRRR                            (R  G  B  A
  117.                                                     c, c, c, c)
  118.      GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____CCCCOOOONNNNSSSSTTTTAAAANNNNTTTT____CCCCOOOOLLLLOOOORRRR          (1, 1, 1, 1) - (R  G  B  A
  119.                                                            c, c, c, c)
  120.      GGGGLLLL____CCCCOOOONNNNSSSSTTTTAAAANNNNTTTT____AAAALLLLPPPPHHHHAAAA                            (A  A  A  A
  121.                                                     c, c, c, c)
  122.      GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____CCCCOOOONNNNSSSSTTTTAAAANNNNTTTT____AAAALLLLPPPPHHHHAAAA          (1, 1, 1, 1) - (A  A  A  A
  123.                                                            c, c, c, c)
  124.      _________________________________________________________________________
  125.  
  126.  
  127.      In the table,
  128.  
  129.                i = min(A , k  - A ) / k
  130.                         s   A    d     A
  131.  
  132.      To determine the blended RGBA values of a pixel when drawing in RGBA
  133.      mode, the system uses the following equations:
  134.  
  135.                R  = min(k   R  s  + R  d )
  136.                 d        R,  s  R    d  R
  137.                G  = min(k   G  s  + G  d )
  138.                 d        G,  s  G    d  G
  139.                B  = min(k   B  s  + B  d )
  140.                 d        B,  s  B    d  B
  141.                A  = min(k   A  s  + A  d )
  142.                 d        A,  s  A    d  A
  143.  
  144.      Despite the apparent precision of the above equations, blending
  145.      arithmetic is not exactly specified, because blending operates with
  146.      imprecise integer color values.  However, a blend factor that should be
  147.      equal to 1 is guaranteed not to modify its multiplicand, and a blend
  148.      factor equal to 0 reduces its multiplicand to 0.  For example, when
  149.      _s_f_a_c_t_o_r is GGGGLLLL____SSSSRRRRCCCC____AAAALLLLPPPPHHHHAAAA, _d_f_a_c_t_o_r is GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____SSSSRRRRCCCC____AAAALLLLPPPPHHHHAAAA, and A  is
  150.                                                                       s
  151.      equal to k , the equations reduce to simple replacement:
  152.                A
  153.  
  154.  
  155.  
  156.  
  157.  
  158.  
  159.  
  160.                                                                         PPPPaaaaggggeeee 2222
  161.  
  162.  
  163.  
  164.  
  165.  
  166.  
  167. ggggllllBBBBlllleeeennnnddddFFFFuuuunnnncccc((((3333GGGG))))                OOOOppppeeeennnnGGGGLLLL RRRReeeeffffeeeerrrreeeennnncccceeee                ggggllllBBBBlllleeeennnnddddFFFFuuuunnnncccc((((3333GGGG))))
  168.  
  169.  
  170.  
  171.                R  = R
  172.                 d    s
  173.                G  = G
  174.                 d    s
  175.                B  = B
  176.                 d    s
  177.                A  = A
  178.                 d    s
  179.  
  180. EEEEXXXXAAAAMMMMPPPPLLLLEEEESSSS
  181.      Transparency is best implemented using blend function (GGGGLLLL____SSSSRRRRCCCC____AAAALLLLPPPPHHHHAAAA,
  182.      GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____SSSSRRRRCCCC____AAAALLLLPPPPHHHHAAAA) with primitives sorted from farthest to nearest.
  183.      Note that this transparency calculation does not require the presence of
  184.      alpha bitplanes in the frame buffer.
  185.  
  186.      Blend function (GGGGLLLL____SSSSRRRRCCCC____AAAALLLLPPPPHHHHAAAA, GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____SSSSRRRRCCCC____AAAALLLLPPPPHHHHAAAA) is also useful for
  187.      rendering antialiased points and lines in arbitrary order.
  188.  
  189.      Polygon antialiasing is optimized using blend function
  190.      (GGGGLLLL____SSSSRRRRCCCC____AAAALLLLPPPPHHHHAAAA____SSSSAAAATTTTUUUURRRRAAAATTTTEEEE, GGGGLLLL____OOOONNNNEEEE) with polygons sorted from nearest to
  191.      farthest.  (See the ggggllllEEEEnnnnaaaabbbblllleeee, ggggllllDDDDiiiissssaaaabbbblllleeee reference page and the
  192.      GGGGLLLL____PPPPOOOOLLLLYYYYGGGGOOOONNNN____SSSSMMMMOOOOOOOOTTTTHHHH argument for information on polygon antialiasing.)
  193.      Destination alpha bitplanes, which must be present for this blend
  194.      function to operate correctly, store the accumulated coverage.
  195.  
  196. NNNNOOOOTTTTEEEESSSS
  197.      Incoming (source) alpha is correctly thought of as a material opacity,
  198.      ranging from 1.0 (K ), representing complete opacity, to 0.0 (0),
  199.                         A
  200.      representing complete transparency.
  201.  
  202.      When more than one color buffer is enabled for drawing, the GL performs
  203.      blending separately for each enabled buffer, using the contents of that
  204.      buffer for destination color.  (See ggggllllDDDDrrrraaaawwwwBBBBuuuuffffffffeeeerrrr.)
  205.  
  206.      Blending affects only RGBA rendering.  It is ignored by color index
  207.      renderers.
  208.  
  209.      GGGGLLLL____CCCCOOOONNNNSSSSTTTTAAAANNNNTTTT____CCCCOOOOLLLLOOOORRRR, GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____CCCCOOOONNNNSSSSTTTTAAAANNNNTTTT____CCCCOOOOLLLLOOOORRRR, GGGGLLLL____CCCCOOOONNNNSSSSTTTTAAAANNNNTTTT____AAAALLLLPPPPHHHHAAAA,
  210.      GGGGLLLL____OOOONNNNEEEE____MMMMIIIINNNNUUUUSSSS____CCCCOOOONNNNSSSSTTTTAAAANNNNTTTT____AAAALLLLPPPPHHHHAAAA are only available if the GGGGLLLL____AAAARRRRBBBB____iiiimmmmaaaaggggiiiinnnngggg is
  211.      supported by your implementation.
  212.  
  213. EEEERRRRRRRROOOORRRRSSSS
  214.      GGGGLLLL____IIIINNNNVVVVAAAALLLLIIIIDDDD____EEEENNNNUUUUMMMM is generated if either _s_f_a_c_t_o_r or _d_f_a_c_t_o_r is not an
  215.      accepted value.
  216.  
  217.      GGGGLLLL____IIIINNNNVVVVAAAALLLLIIIIDDDD____OOOOPPPPEEEERRRRAAAATTTTIIIIOOOONNNN is generated if ggggllllBBBBlllleeeennnnddddFFFFuuuunnnncccc is executed between the
  218.      execution of ggggllllBBBBeeeeggggiiiinnnn and the corresponding execution of ggggllllEEEEnnnndddd.
  219.  
  220. AAAASSSSSSSSOOOOCCCCIIIIAAAATTTTEEEEDDDD GGGGEEEETTTTSSSS
  221.      ggggllllGGGGeeeetttt with argument GGGGLLLL____BBBBLLLLEEEENNNNDDDD____SSSSRRRRCCCC
  222.      ggggllllGGGGeeeetttt with argument GGGGLLLL____BBBBLLLLEEEENNNNDDDD____DDDDSSSSTTTT
  223.      ggggllllIIIIssssEEEEnnnnaaaabbbblllleeeedddd with argument GGGGLLLL____BBBBLLLLEEEENNNNDDDD
  224.  
  225.  
  226.  
  227.  
  228.  
  229.  
  230.  
  231.                                                                         PPPPaaaaggggeeee 3333
  232.  
  233.  
  234.  
  235.  
  236.  
  237.  
  238. ggggllllBBBBlllleeeennnnddddFFFFuuuunnnncccc((((3333GGGG))))                OOOOppppeeeennnnGGGGLLLL RRRReeeeffffeeeerrrreeeennnncccceeee                ggggllllBBBBlllleeeennnnddddFFFFuuuunnnncccc((((3333GGGG))))
  239.  
  240.  
  241.  
  242. MMMMAAAACCCCHHHHIIIINNNNEEEE DDDDEEEEPPPPEEEENNNNDDDDEEEENNNNCCCCIIIIEEEESSSS
  243.      RRRReeeeaaaalllliiiittttyyyyEEEEnnnnggggiiiinnnneeee, RRRReeeeaaaalllliiiittttyyyyEEEEnnnnggggiiiinnnneeee2222, and VVVVTTTTXXXX systems do not support the use of
  244.      source blend factor GGGGLLLL____SSSSRRRRCCCC____AAAALLLLPPPPHHHHAAAA____SSSSAAAATTTTUUUURRRRAAAATTTTEEEE and a destination factor based
  245.      on the constant blend color (GGGGLLLL____........____CCCCOOOONNNNSSSSTTTTAAAANNNNTTTT____........____EEEEXXXXTTTT); such combinations
  246.      produce incorrect results.
  247.  
  248.  
  249. SSSSEEEEEEEE AAAALLLLSSSSOOOO
  250.      ggggllllAAAAllllpppphhhhaaaaFFFFuuuunnnncccc, ggggllllBBBBlllleeeennnnddddCCCCoooolllloooorrrr, ggggllllBBBBlllleeeennnnddddEEEEqqqquuuuaaaattttiiiioooonnnn, ggggllllCCCClllleeeeaaaarrrr, ggggllllDDDDrrrraaaawwwwBBBBuuuuffffffffeeeerrrr,
  251.      ggggllllEEEEnnnnaaaabbbblllleeee, ggggllllLLLLooooggggiiiiccccOOOOpppp, ggggllllSSSStttteeeennnncccciiiillllFFFFuuuunnnncccc
  252.  
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  293.  
  294.  
  295.  
  296.  
  297.                                                                         PPPPaaaaggggeeee 4444
  298.  
  299.  
  300.  
  301.