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Text File  |  2002-10-03  |  7.1 KB  |  133 lines
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  4. ffffggggllllAAAAllllpppphhhhaaaaFFFFuuuunnnncccc((((3333GGGG))))               OOOOppppeeeennnnGGGGLLLL RRRReeeeffffeeeerrrreeeennnncccceeee               ffffggggllllAAAAllllpppphhhhaaaaFFFFuuuunnnncccc((((3333GGGG))))
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  7.  
  8. NNNNAAAAMMMMEEEE
  9.      ffffggggllllAAAAllllpppphhhhaaaaFFFFuuuunnnncccc - specify the alpha test function
  10.  
  11.  
  12. FFFFOOOORRRRTTTTRRRRAAAANNNN SSSSPPPPEEEECCCCIIIIFFFFIIIICCCCAAAATTTTIIIIOOOONNNN
  13.      SUBROUTINE ffffggggllllAAAAllllpppphhhhaaaaFFFFuuuunnnncccc( INTEGER*4 _f_u_n_c,
  14.                               REAL*4 _r_e_f )
  15.  
  16.  
  17. PPPPAAAARRRRAAAAMMMMEEEETTTTEEEERRRRSSSS
  18.      _f_u_n_c  Specifies the alpha comparison function.  Symbolic constants
  19.            GGGGLLLL____NNNNEEEEVVVVEEEERRRR, GGGGLLLL____LLLLEEEESSSSSSSS, GGGGLLLL____EEEEQQQQUUUUAAAALLLL, GGGGLLLL____LLLLEEEEQQQQUUUUAAAALLLL, GGGGLLLL____GGGGRRRREEEEAAAATTTTEEEERRRR, GGGGLLLL____NNNNOOOOTTTTEEEEQQQQUUUUAAAALLLL,
  20.            GGGGLLLL____GGGGEEEEQQQQUUUUAAAALLLL, and GGGGLLLL____AAAALLLLWWWWAAAAYYYYSSSS are accepted. The initial value is
  21.            GGGGLLLL____AAAALLLLWWWWAAAAYYYYSSSS.
  22.  
  23.      _r_e_f   Specifies the reference value that incoming alpha values are
  24.            compared to.  This value is clamped to the range [0, 1], where 0
  25.            represents the lowest possible alpha value and 1 the highest
  26.            possible value.  The initial reference value is 0.
  27.  
  28. DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
  29.      The alpha test discards fragments depending on the outcome of a
  30.      comparison between an incoming fragment's alpha value and a constant
  31.      reference value.  ffffggggllllAAAAllllpppphhhhaaaaFFFFuuuunnnncccc specifies the reference value and the
  32.      comparison function.  The comparison is performed only if alpha testing
  33.      is enabled. By default, it is not enabled. (See ffffggggllllEEEEnnnnaaaabbbblllleeee and ffffggggllllDDDDiiiissssaaaabbbblllleeee
  34.      of GGGGLLLL____AAAALLLLPPPPHHHHAAAA____TTTTEEEESSSSTTTT.)
  35.  
  36.      _f_u_n_c and _r_e_f specify the conditions under which the pixel is drawn.  The
  37.      incoming alpha value is compared to _r_e_f using the function specified by
  38.      _f_u_n_c.  If the value passes the comparison, the incoming fragment is drawn
  39.      if it also passes subsequent stencil and depth buffer tests. If the value
  40.      fails the comparison, no change is made to the frame buffer at that pixel
  41.      location. The comparison functions are as follows:
  42.  
  43.      GGGGLLLL____NNNNEEEEVVVVEEEERRRR          Never passes.
  44.  
  45.      GGGGLLLL____LLLLEEEESSSSSSSS           Passes if the incoming alpha value is less than the
  46.                        reference value.
  47.  
  48.      GGGGLLLL____EEEEQQQQUUUUAAAALLLL          Passes if the incoming alpha value is equal to the
  49.                        reference value.
  50.  
  51.      GGGGLLLL____LLLLEEEEQQQQUUUUAAAALLLL         Passes if the incoming alpha value is less than or
  52.                        equal to the reference value.
  53.  
  54.      GGGGLLLL____GGGGRRRREEEEAAAATTTTEEEERRRR        Passes if the incoming alpha value is greater than the
  55.                        reference value.
  56.  
  57.      GGGGLLLL____NNNNOOOOTTTTEEEEQQQQUUUUAAAALLLL       Passes if the incoming alpha value is not equal to the
  58.                        reference value.
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  62.  
  63.                                                                         PPPPaaaaggggeeee 1111
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  70. ffffggggllllAAAAllllpppphhhhaaaaFFFFuuuunnnncccc((((3333GGGG))))               OOOOppppeeeennnnGGGGLLLL RRRReeeeffffeeeerrrreeeennnncccceeee               ffffggggllllAAAAllllpppphhhhaaaaFFFFuuuunnnncccc((((3333GGGG))))
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  74.      GGGGLLLL____GGGGEEEEQQQQUUUUAAAALLLL         Passes if the incoming alpha value is greater than or
  75.                        equal to the reference value.
  76.  
  77.      GGGGLLLL____AAAALLLLWWWWAAAAYYYYSSSS         Always passes (initial value).
  78.  
  79.      ffffggggllllAAAAllllpppphhhhaaaaFFFFuuuunnnncccc operates on all pixel write operations, including those
  80.      resulting from the scan conversion of points, lines, polygons, and
  81.      bitmaps, and from pixel draw and copy operations.  ffffggggllllAAAAllllpppphhhhaaaaFFFFuuuunnnncccc does not
  82.      affect screen clear operations.
  83.  
  84. NNNNOOOOTTTTEEEESSSS
  85.      Alpha testing is performed only in RGBA mode.
  86.  
  87. EEEERRRRRRRROOOORRRRSSSS
  88.      GGGGLLLL____IIIINNNNVVVVAAAALLLLIIIIDDDD____EEEENNNNUUUUMMMM is generated if _f_u_n_c is not an accepted value.
  89.  
  90.      GGGGLLLL____IIIINNNNVVVVAAAALLLLIIIIDDDD____OOOOPPPPEEEERRRRAAAATTTTIIIIOOOONNNN is generated if ffffggggllllAAAAllllpppphhhhaaaaFFFFuuuunnnncccc is executed between the
  91.      execution of ffffggggllllBBBBeeeeggggiiiinnnn and the corresponding execution of ffffggggllllEEEEnnnndddd.
  92.  
  93. AAAASSSSSSSSOOOOCCCCIIIIAAAATTTTEEEEDDDD GGGGEEEETTTTSSSS
  94.      ffffggggllllGGGGeeeetttt with argument GGGGLLLL____AAAALLLLPPPPHHHHAAAA____TTTTEEEESSSSTTTT____FFFFUUUUNNNNCCCC
  95.      ffffggggllllGGGGeeeetttt with argument GGGGLLLL____AAAALLLLPPPPHHHHAAAA____TTTTEEEESSSSTTTT____RRRREEEEFFFF
  96.      ffffggggllllIIIIssssEEEEnnnnaaaabbbblllleeeedddd with argument GGGGLLLL____AAAALLLLPPPPHHHHAAAA____TTTTEEEESSSSTTTT
  97.  
  98.  
  99. SSSSEEEEEEEE AAAALLLLSSSSOOOO
  100.      ffffggggllllBBBBlllleeeennnnddddFFFFuuuunnnncccc, ffffggggllllCCCClllleeeeaaaarrrr, ffffggggllllDDDDeeeepppptttthhhhFFFFuuuunnnncccc, ffffggggllllEEEEnnnnaaaabbbblllleeee, ffffggggllllSSSStttteeeennnncccciiiillllFFFFuuuunnnncccc
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  129.                                                                         PPPPaaaaggggeeee 2222
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