glStencilFunc(3gl)

1GLSTENCILFUNC(3G)                                            GLSTENCILFUNC(3G)
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NAME

6       glStencilFunc - set function and reference value for stencil testing
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C SPECIFICATION

10       void glStencilFunc( GLenum func,
11                           GLint ref,
12                           GLuint mask )
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PARAMETERS

16       func  Specifies  the  test function.  Eight tokens are valid: GL_NEVER,
17             GL_LESS, GL_LEQUAL, GL_GREATER, GL_GEQUAL, GL_EQUAL, GL_NOTEQUAL,
18             and GL_ALWAYS. The initial value is GL_ALWAYS.
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20       ref   Specifies  the  reference  value  for  the  stencil test.  ref is
21             clamped to the range [0,2n−1], where n is the number of bitplanes
22             in the stencil buffer. The initial value is 0.
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24       mask  Specifies  a mask that is ANDed with both the reference value and
25             the stored stencil value when the test is done. The initial value
26             is all 1's.
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DESCRIPTION

29       Stenciling,  like  depth-buffering,  enables  and disables drawing on a
30       per-pixel basis.  You draw into the stencil  planes  using  GL  drawing
31       primitives,  then  render geometry and images, using the stencil planes
32       to mask out portions of the screen.  Stenciling is  typically  used  in
33       multipass  rendering  algorithms  to  achieve  special effects, such as
34       decals, outlining, and constructive solid geometry rendering.
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36       The stencil test conditionally eliminates a pixel based on the  outcome
37       of  a comparison between the reference value and the value in the sten‐
38       cil buffer.   To  enable  and  disable  the  test,  call  glEnable  and
39       glDisable  with  argument GL_STENCIL_TEST.  To specify actions based on
40       the outcome of the stencil test, call glStencilOp.
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42       func is a symbolic constant  that  determines  the  stencil  comparison
43       function.  It accepts one of eight values, shown in the following list.
44       ref is an integer reference value that is used in the stencil  compari‐
45       son.   It  is  clamped  to the range [0,2n−1], where n is the number of
46       bitplanes in the stencil buffer.  mask is bitwise ANDed with  both  the
47       reference  value  and  the  stored stencil value, with the ANDed values
48       participating in the comparison.
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50       If stencil represents the value stored  in  the  corresponding  stencil
51       buffer location, the following list shows the effect of each comparison
52       function that can be specified by func.  Only if  the  comparison  suc‐
53       ceeds  is  the pixel passed through to the next stage in the rasteriza‐
54       tion process (see glStencilOp).  All  tests  treat  stencil  values  as
55       unsigned  integers in the range [0,2n−1], where n is the number of bit‐
56       planes in the stencil buffer.
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58       The following values are accepted by func:
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60       GL_NEVER          Always fails.
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62       GL_LESS           Passes if ( ref & mask ) < ( stencil & mask ).
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64       GL_LEQUAL         Passes if ( ref & mask ) ≤ ( stencil & mask ).
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66       GL_GREATER        Passes if ( ref & mask ) > ( stencil & mask ).
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68       GL_GEQUAL         Passes if ( ref & mask ) ≥ ( stencil & mask ).
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70       GL_EQUAL          Passes if ( ref & mask ) = ( stencil & mask ).
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72       GL_NOTEQUAL       Passes if ( ref & mask ) ≠  ( stencil & mask ).
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74       GL_ALWAYS         Always passes.
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NOTES

77       Initially, the stencil test is disabled.  If there is no  stencil  buf‐
78       fer, no stencil modification can occur and it is as if the stencil test
79       always passes.
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ERRORS

82       GL_INVALID_ENUM is generated if func is not one of the  eight  accepted
83       values.
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85       GL_INVALID_OPERATION  is generated if glStencilFunc is executed between
86       the execution of glBegin and the corresponding execution of glEnd.
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ASSOCIATED GETS

89       glGet with argument GL_STENCIL_FUNC
90       glGet with argument GL_STENCIL_VALUE_MASK
91       glGet with argument GL_STENCIL_REF
92       glGet with argument GL_STENCIL_BITS
93       glIsEnabled with argument GL_STENCIL_TEST
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