GLAPI/glStencilOp: Difference between revisions

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== Function Definition ==
== Function Definition ==


   void '''glStencilOp'''(GLenum ''sfail'', GLenum ''dpfail'', GLenum ''dppass'');
   void '''glStencilOp'''(GLenum {{param|sfail}}, GLenum {{param|dpfail}}, GLenum {{param|dppass}});


; sfail
; sfail
: Specifies the action to take when the stencil test fails. Eight symbolic constants are accepted: {{code|GL_KEEP}}, {{code|GL_ZERO}}, {{code|GL_REPLACE}}, {{code|GL_INCR}}, {{code|GL_INCR_WRAP}}, {{code|GL_DECR}}, {{code|GL_DECR_WRAP}}, and {{code|GL_INVERT}}. The initial value is {{code|GL_KEEP}}.
: Specifies the action to take when the stencil test fails. Eight symbolic constants are accepted: {{enum|GL_KEEP}}, {{enum|GL_ZERO}}, {{enum|GL_REPLACE}}, {{enum|GL_INCR}}, {{enum|GL_INCR_WRAP}}, {{enum|GL_DECR}}, {{enum|GL_DECR_WRAP}}, and {{enum|GL_INVERT}}. The initial value is {{enum|GL_KEEP}}.
; dpfail
; dpfail
: Specifies the stencil action when the stencil test passes, but the depth test fails. ''dpfail'' accepts the same symbolic constants as ''sfail''. The initial value is {{code|GL_KEEP}}.
: Specifies the stencil action when the stencil test passes, but the depth test fails. {{param|dpfail}} accepts the same symbolic constants as {{param|sfail}}. The initial value is {{enum|GL_KEEP}}.
; dppass
; dppass
: Specifies the stencil action when both the stencil test and the depth test pass, or when the stencil test passes and either there is no depth buffer or depth testing is not enabled. ''dppass'' accepts the same symbolic constants as ''sfail''. The initial value is {{code|GL_KEEP}}.
: Specifies the stencil action when both the stencil test and the depth test pass, or when the stencil test passes and either there is no depth buffer or depth testing is not enabled. {{param|dppass}} accepts the same symbolic constants as {{param|sfail}}. The initial value is {{enum|GL_KEEP}}.


== Description ==
== Description ==
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Stenciling, like depth-buffering, enables and disables drawing on a per-pixel basis. You draw into the stencil planes using GL drawing primitives, then render geometry and images, using the stencil planes to mask out portions of the screen. Stenciling is typically used in multipass rendering algorithms to achieve special effects, such as decals, outlining, and constructive solid geometry rendering.
Stenciling, like depth-buffering, enables and disables drawing on a per-pixel basis. You draw into the stencil planes using GL drawing primitives, then render geometry and images, using the stencil planes to mask out portions of the screen. Stenciling is typically used in multipass rendering algorithms to achieve special effects, such as decals, outlining, and constructive solid geometry rendering.


The stencil test conditionally eliminates a pixel based on the outcome of a comparison between the value in the stencil buffer and a reference value. To enable and disable the test, call [[GLAPI/glEnable|glEnable]] and [[GLAPI/glDisable|glDisable]] with argument {{code|GL_STENCIL_TEST}}; to control it, call [[GLAPI/glStencilFunc|glStencilFunc]] or [[GLAPI/glStencilFuncSeparate|glStencilFuncSeparate]].
The stencil test conditionally eliminates a pixel based on the outcome of a comparison between the value in the stencil buffer and a reference value. To enable and disable the test, call {{apifunc|glEnable}} and {{apifunc|glDisable}} with argument {{enum|GL_STENCIL_TEST}}; to control it, call {{apifunc|glStencilFunc}} or {{apifunc|glStencilFuncSeparate}}.


There can be two separate sets of ''sfail'', ''dpfail'', and ''dppass'' parameters; one affects back-facing polygons, and the other affects front-facing polygons as well as other non-polygon primitives. [[GLAPI/glStencilOp|glStencilOp]] sets both front and back stencil state to the same values. Use [[GLAPI/glStencilOpSeparate|glStencilOpSeparate]] to set front and back stencil state to different values.
There can be two separate sets of {{param|sfail}}, {{param|dpfail}}, and {{param|dppass}} parameters; one affects back-facing polygons, and the other affects front-facing polygons as well as other non-polygon primitives. {{apifunc|glStencilOp}} sets both front and back stencil state to the same values. Use {{apifunc|glStencilOpSeparate}} to set front and back stencil state to different values.


'''glStencilOp''' takes three arguments that indicate what happens to the stored stencil value while stenciling is enabled. If the stencil test fails, no change is made to the pixel's color or depth buffers, and ''sfail'' specifies what happens to the stencil buffer contents. The following eight actions are possible.
'''glStencilOp''' takes three arguments that indicate what happens to the stored stencil value while stenciling is enabled. If the stencil test fails, no change is made to the pixel's color or depth buffers, and {{param|sfail}} specifies what happens to the stencil buffer contents. The following eight actions are possible.


; {{code|GL_KEEP}}
; {{enum|GL_KEEP}}
: Keeps the current value.
: Keeps the current value.
; {{code|GL_ZERO}}
; {{enum|GL_ZERO}}
: Sets the stencil buffer value to 0.
: Sets the stencil buffer value to 0.
; {{code|GL_REPLACE}}
; {{enum|GL_REPLACE}}
: Sets the stencil buffer value to ''ref'', as specified by [[GLAPI/glStencilFunc|glStencilFunc]].
: Sets the stencil buffer value to ''ref'', as specified by {{apifunc|glStencilFunc}}.
; {{code|GL_INCR}}
; {{enum|GL_INCR}}
: Increments the current stencil buffer value. Clamps to the maximum representable unsigned value.
: Increments the current stencil buffer value. Clamps to the maximum representable unsigned value.
; {{code|GL_INCR_WRAP}}
; {{enum|GL_INCR_WRAP}}
: Increments the current stencil buffer value. Wraps stencil buffer value to zero when incrementing the maximum representable unsigned value.
: Increments the current stencil buffer value. Wraps stencil buffer value to zero when incrementing the maximum representable unsigned value.
; {{code|GL_DECR}}
; {{enum|GL_DECR}}
: Decrements the current stencil buffer value. Clamps to 0.
: Decrements the current stencil buffer value. Clamps to 0.
; {{code|GL_DECR_WRAP}}
; {{enum|GL_DECR_WRAP}}
: Decrements the current stencil buffer value. Wraps stencil buffer value to the maximum representable unsigned value when decrementing a stencil buffer value of zero.
: Decrements the current stencil buffer value. Wraps stencil buffer value to the maximum representable unsigned value when decrementing a stencil buffer value of zero.
; {{code|GL_INVERT}}
; {{enum|GL_INVERT}}
: Bitwise inverts the current stencil buffer value.
: Bitwise inverts the current stencil buffer value.
Stencil buffer values are treated as unsigned integers. When incremented and decremented, values are clamped to 0 and <!--Missing Equation-->, where <!--Missing Equation--> is the value returned by querying {{code|GL_STENCIL_BITS}}.
Stencil buffer values are treated as unsigned integers. When incremented and decremented, values are clamped to 0 and 2<sup>n</sup> - 1, where ''n'' is the value returned by querying {{enum|GL_STENCIL_BITS}}.


The other two arguments to '''glStencilOp''' specify stencil buffer actions that depend on whether subsequent depth buffer tests succeed (''dppass'') or fail (''dpfail'') (see [[GLAPI/glDepthFunc|glDepthFunc]]). The actions are specified using the same eight symbolic constants as ''sfail''. Note that ''dpfail'' is ignored when there is no depth buffer, or when the depth buffer is not enabled. In these cases, ''sfail'' and ''dppass'' specify stencil action when the stencil test fails and passes, respectively.
The other two arguments to '''glStencilOp''' specify stencil buffer actions that depend on whether subsequent depth buffer tests succeed ({{param|dppass}}) or fail ({{param|dpfail}}) (see {{apifunc|glDepthFunc}}). The actions are specified using the same eight symbolic constants as {{param|sfail}}. Note that {{param|dpfail}} is ignored when there is no depth buffer, or when the depth buffer is not enabled. In these cases, {{param|sfail}} and {{param|dppass}} specify stencil action when the stencil test fails and passes, respectively.


== Notes ==
== Notes ==
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Initially the stencil test is disabled. If there is no stencil buffer, no stencil modification can occur and it is as if the stencil tests always pass, regardless of any call to '''glStencilOp'''.
Initially the stencil test is disabled. If there is no stencil buffer, no stencil modification can occur and it is as if the stencil tests always pass, regardless of any call to '''glStencilOp'''.


[[GLAPI/glStencilOp|glStencilOp]] is the same as calling [[GLAPI/glStencilOpSeparate|glStencilOpSeparate]] with ''face'' set to {{code|GL_FRONT_AND_BACK}}.
{{apifunc|glStencilOp}} is the same as calling {{apifunc|glStencilOpSeparate}} with {{param|face}} set to {{enum|GL_FRONT_AND_BACK}}.


== Errors ==
== Errors ==


{{code|GL_INVALID_ENUM}} is generated if ''sfail'', ''dpfail'', or ''dppass'' is any value other than the defined constant values.
{{enum|GL_INVALID_ENUM}} is generated if {{param|sfail}}, {{param|dpfail}}, or {{param|dppass}} is any value other than the defined constant values.


== Associated Gets ==
== Associated Gets ==


[[GLAPI/glGet|glGet]] with argument {{code|GL_STENCIL_FAIL}}, {{code|GL_STENCIL_PASS_DEPTH_PASS}}, {{code|GL_STENCIL_PASS_DEPTH_FAIL}}, {{code|GL_STENCIL_BACK_FAIL}}, {{code|GL_STENCIL_BACK_PASS_DEPTH_PASS}}, {{code|GL_STENCIL_BACK_PASS_DEPTH_FAIL}}, or {{code|GL_STENCIL_BITS}}
{{apifunc|glGet}} with argument {{enum|GL_STENCIL_FAIL}}, {{enum|GL_STENCIL_PASS_DEPTH_PASS}}, {{enum|GL_STENCIL_PASS_DEPTH_FAIL}}, {{enum|GL_STENCIL_BACK_FAIL}}, {{enum|GL_STENCIL_BACK_PASS_DEPTH_PASS}}, {{enum|GL_STENCIL_BACK_PASS_DEPTH_FAIL}}, or {{enum|GL_STENCIL_BITS}}


[[GLAPI/glIsEnabled|glIsEnabled]] with argument {{code|GL_STENCIL_TEST}}
{{apifunc|glIsEnabled}} with argument {{enum|GL_STENCIL_TEST}}


== See Also ==
== See Also ==


[[GLAPI/glBlendFunc|glBlendFunc]], [[GLAPI/glDepthFunc|glDepthFunc]], [[GLAPI/glEnable|glEnable]], [[GLAPI/glLogicOp|glLogicOp]], [[GLAPI/glStencilFunc|glStencilFunc]], [[GLAPI/glStencilFuncSeparate|glStencilFuncSeparate]], [[GLAPI/glStencilMask|glStencilMask]], [[GLAPI/glStencilMaskSeparate|glStencilMaskSeparate]], [[GLAPI/glStencilOpSeparate|glStencilOpSeparate]]
{{apifunc|glBlendFunc}}, {{apifunc|glDepthFunc}}, {{apifunc|glEnable}}, {{apifunc|glLogicOp}}, {{apifunc|glStencilFunc}}, {{apifunc|glStencilFuncSeparate}}, {{apifunc|glStencilMask}}, {{apifunc|glStencilMaskSeparate}}, {{apifunc|glStencilOpSeparate}}


== Copyright ==
== Copyright ==


Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see [http://oss.sgi.com/projects/FreeB/ http://oss.sgi.com/projects/FreeB/].
Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see [https://khronos.org/registry/OpenGL-Refpages/LICENSES/LicenseRef-FreeB.txt LicenseRef-FreeB].


[[Category:API Reference 4|StencilOp]]
[[Category:Core API Ref Post Fragment Shader Operations|StencilOp]]
[[Category:Core API Reference|StencilOp]]

Latest revision as of 22:17, 5 February 2021

glStencilOp
Core in version 4.6
Core since version 1.0

glStencilOp: set front and back stencil test actions

Function Definition

 void glStencilOp(GLenum sfail​, GLenum dpfail​, GLenum dppass​);
sfail
Specifies the action to take when the stencil test fails. Eight symbolic constants are accepted: GL_KEEP, GL_ZERO, GL_REPLACE, GL_INCR, GL_INCR_WRAP, GL_DECR, GL_DECR_WRAP, and GL_INVERT. The initial value is GL_KEEP.
dpfail
Specifies the stencil action when the stencil test passes, but the depth test fails. dpfail​ accepts the same symbolic constants as sfail​. The initial value is GL_KEEP.
dppass
Specifies the stencil action when both the stencil test and the depth test pass, or when the stencil test passes and either there is no depth buffer or depth testing is not enabled. dppass​ accepts the same symbolic constants as sfail​. The initial value is GL_KEEP.

Description

Stenciling, like depth-buffering, enables and disables drawing on a per-pixel basis. You draw into the stencil planes using GL drawing primitives, then render geometry and images, using the stencil planes to mask out portions of the screen. Stenciling is typically used in multipass rendering algorithms to achieve special effects, such as decals, outlining, and constructive solid geometry rendering.

The stencil test conditionally eliminates a pixel based on the outcome of a comparison between the value in the stencil buffer and a reference value. To enable and disable the test, call glEnable and glDisable with argument GL_STENCIL_TEST; to control it, call glStencilFunc or glStencilFuncSeparate.

There can be two separate sets of sfail​, dpfail​, and dppass​ parameters; one affects back-facing polygons, and the other affects front-facing polygons as well as other non-polygon primitives. glStencilOp sets both front and back stencil state to the same values. Use glStencilOpSeparate to set front and back stencil state to different values.

glStencilOp takes three arguments that indicate what happens to the stored stencil value while stenciling is enabled. If the stencil test fails, no change is made to the pixel's color or depth buffers, and sfail​ specifies what happens to the stencil buffer contents. The following eight actions are possible.

GL_KEEP
Keeps the current value.
GL_ZERO
Sets the stencil buffer value to 0.
GL_REPLACE
Sets the stencil buffer value to ref, as specified by glStencilFunc.
GL_INCR
Increments the current stencil buffer value. Clamps to the maximum representable unsigned value.
GL_INCR_WRAP
Increments the current stencil buffer value. Wraps stencil buffer value to zero when incrementing the maximum representable unsigned value.
GL_DECR
Decrements the current stencil buffer value. Clamps to 0.
GL_DECR_WRAP
Decrements the current stencil buffer value. Wraps stencil buffer value to the maximum representable unsigned value when decrementing a stencil buffer value of zero.
GL_INVERT
Bitwise inverts the current stencil buffer value.

Stencil buffer values are treated as unsigned integers. When incremented and decremented, values are clamped to 0 and 2n - 1, where n is the value returned by querying GL_STENCIL_BITS.

The other two arguments to glStencilOp specify stencil buffer actions that depend on whether subsequent depth buffer tests succeed (dppass​) or fail (dpfail​) (see glDepthFunc). The actions are specified using the same eight symbolic constants as sfail​. Note that dpfail​ is ignored when there is no depth buffer, or when the depth buffer is not enabled. In these cases, sfail​ and dppass​ specify stencil action when the stencil test fails and passes, respectively.

Notes

Initially the stencil test is disabled. If there is no stencil buffer, no stencil modification can occur and it is as if the stencil tests always pass, regardless of any call to glStencilOp.

glStencilOp is the same as calling glStencilOpSeparate with face​ set to GL_FRONT_AND_BACK.

Errors

GL_INVALID_ENUM is generated if sfail​, dpfail​, or dppass​ is any value other than the defined constant values.

Associated Gets

glGet with argument GL_STENCIL_FAIL, GL_STENCIL_PASS_DEPTH_PASS, GL_STENCIL_PASS_DEPTH_FAIL, GL_STENCIL_BACK_FAIL, GL_STENCIL_BACK_PASS_DEPTH_PASS, GL_STENCIL_BACK_PASS_DEPTH_FAIL, or GL_STENCIL_BITS

glIsEnabled with argument GL_STENCIL_TEST

See Also

glBlendFunc, glDepthFunc, glEnable, glLogicOp, glStencilFunc, glStencilFuncSeparate, glStencilMask, glStencilMaskSeparate, glStencilOpSeparate

Copyright

Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see LicenseRef-FreeB.

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