glBlendEquation(3gl)

1GLBLENDEQUATION(3G)                                        GLBLENDEQUATION(3G)
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NAME

6       glBlendEquation - set the blend equation
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C SPECIFICATION

10       void glBlendEquation( GLenum mode )
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PARAMETERS

14       mode  specifies  how  source  and  destination colors are combined.  It
15             must be GL_FUNC_ADD, GL_FUNC_SUBTRACT,  GL_FUNC_REVERSE_SUBTRACT,
16             GL_MIN, GL_MAX.
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DESCRIPTION

20       The blend equation determines how a new pixel (the ``source'' color) is
21       combined with a pixel already in the framebuffer  (the  ``destination''
22       color).
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24       GL_MIN sets  the  blend  equation  so that each component of the result
25              color is the minimum of  the  corresponding  components  of  the
26              source and destination colors.
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28       GL_MAX sets  the  blend  equation  so that each component of the result
29              color is the maximum of  the  corresponding  components  of  the
30              source and destination colors.
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32       The remaining blend equations use the source and destination blend fac‐
33       tors specified by glBlendFunc.  See glBlendFunc for  a  description  of
34       the various blend factors.
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36       In  the  equations that follow, source and destination color components
37       are referred to as (Rs,Gs,Bs,As) and (Rd,Gd,Bd,Ad), respectively.   The
38       result  color is referred to as (Rr,Gr,Br,Ar).  The source and destina‐
39       tion blend factors are denoted (sR,sG,sB,sA) and (dR,dG,dB,dA), respec‐
40       tively.   For  these  equations  all color components are understood to
41       have values in the range [0, 1].
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43       GL_FUNC_ADD
44              sets the blend equation so that the source and destination  data
45              are  added.  Each component of the source color is multiplied by
46              the corresponding source factor, then each component of the des‐
47              tination  color  is  multiplied by the corresponding destination
48              factor.  The result is the componentwise sum of  the  two  prod‐
49              ucts, clamped to the range [0, 1].
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51                     Rr=min(1,RssR+RddR)
52                     Gr=min(1,GssG+GddG)
53                     Br=min(1,BssB+BddB)
54                     Ar=min(1,AssA+AddA)
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56       GL_FUNC_SUBTRACT
57              Is like GL_FUNC_ADD except the product of the destination factor
58              and the destination color is componentwise subtracted  from  the
59              product  of  the source factor and the source color.  The result
60              is clamped to the range [0, 1].
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62                     Rr=max(0,RssR−RddR)
63                     Gr=max(0,GssG−GddG)
64                     Br=max(0,BssB−BddB)
65                     Ar=max(0,AssA−AddA)
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67       GL_FUNC_REVERSE_SUBTRACT
68              Is like GL_FUNC_ADD except the product of the source factor  and
69              the source color is componentwise subtracted from the product of
70              the destination factor and the destination color.  The result is
71              clamped to the range [0, 1].
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73                     Rr=max(0,RddR−RssR)
74                     Gr=max(0,GddG−GssG)
75                     Br=max(0,BddB−BssB)
76                     Ar=max(0,AddA−AssA)
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78       The  GL_MIN  and GL_MAX equations are useful for applications that ana‐
79       lyze
80       image data (image thresholding against a constant color, for  example).
81       The  GL_FUNC_ADD  equation is useful for antialiasing and transparency,
82       among other things.
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84       Initially, the blend equation is set to GL_FUNC_ADD.
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NOTES

87       glBlendEquation is part of the GL_ARB_imaging  subset.  glBlendEquation
88       is  present  only  if  GL_ARB_imaging  is  returned when glGetString is
89       called with GL_EXTENSIONS as its argument.
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91       The GL_MIN, and GL_MAX equations do not use the source  or  destination
92       factors, only the source and destination colors.
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ERRORS

95       GL_INVALID_ENUM  is  generated  if  mode  is  not  one  of GL_FUNC_ADD,
96       GL_FUNC_SUBTRACT, GL_FUNC_REVERSE_SUBTRACT, GL_MAX, or GL_MIN.
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98       GL_INVALID_OPERATION  is  generated  if  glBlendEquation  is   executed
99       between  the  execution  of  glBegin and the corresponding execution of
100       glEnd.
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ASSOCIATED GETS

103       glGet with an argument of GL_BLEND_EQUATION
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