GLSTENCILOPSEPARATE(3G)

    .SH "NAME" glStencilOpSeparate - set front and/or back stencil test actions
    .SH "C SPECIFICATION"

            .HP u void glStencilOpSeparate(GLenum face, GLenum sfail, GLenum dpfail, GLenum dppass);

    .SH "PARAMETERS"

        .PP face

                    Specifies whether front and/or back stencil state is updated. Three symbolic constants are valid: GL_FRONT, GL_BACK, and GL_FRONT_AND_BACK.

            .RE
            .PP 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.

                .RE
                .PP 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.

                    .RE
                    .PP 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.

                        .RE

                    .SH "DESCRIPTION"
                        .PP 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.
                        .PP 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().
                        .PP 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, as if glStencilOpSeparate() were called with face set to GL_FRONT_AND_BACK.
                        .PP glStencilOpSeparate 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.

                            .PP GL_KEEP

                                        Keeps the current value.

                                .RE
                                .PP GL_ZERO

                                            Sets the stencil buffer value to 0.

                                    .RE
                                    .PP GL_REPLACE

                                                Sets the stencil buffer value to ref, as specified by glStencilFunc().

                                        .RE
                                        .PP GL_INCR

                                                    Increments the current stencil buffer value. Clamps to the maximum representable unsigned value.

                                            .RE
                                            .PP GL_INCR_WRAP

                                                        Increments the current stencil buffer value. Wraps stencil buffer value to zero when incrementing the maximum representable unsigned value.

                                                .RE
                                                .PP GL_DECR

                                                            Decrements the current stencil buffer value. Clamps to 0.

                                                    .RE
                                                    .PP 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.

                                                        .RE
                                                        .PP GL_INVERT

                                                                    Bitwise inverts the current stencil buffer value.

                                                            .RE

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

                                                    .SH "NOTES"
                                                        .PP Initially the stencil test is disabled. If there is no stencil buffer, no stencil modification can occur and it is as if the stencil test always passes.

                                                    .SH "ERRORS"
                                                        .PP GL_INVALID_ENUM is generated if face is any value other than GL_FRONT, GL_BACK, or GL_FRONT_AND_BACK.
                                                        .PP GL_INVALID_ENUM is generated if sfail, dpfail, or dppass is any value other than the eight defined constant values.

                                                    .SH "ASSOCIATED GETS"
                                                        .PP 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
                                                        .PP glIsEnabled() with argument GL_STENCIL_TEST

                                                    .SH "VERSION SUPPORT"
                                                        .TS allbox tab(:); lB cB s s s s s s s s s s s lB cB cB cB cB cB cB cB cB cB cB cB cB. T{ T}:T{ OpenGL Version T} T{ Function / Feature Name T}:T{ 2.0 T}:T{ 2.1 T}:T{ 3.0 T}:T{ 3.1 T}:T{ 3.2 T}:T{ 3.3 T}:T{ 4.0 T}:T{ 4.1 T}:T{ 4.2 T}:T{ 4.3 T}:T{ 4.4 T}:T{ 4.5 T} l c c c c c c c c c c c c. T{ glStencilOpSeparate T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}

                                                    .SH "SEE ALSO"
                                                        .PP glBlendFunc(), glDepthFunc(), glEnable(), glLogicOp(), glStencilFunc(), glStencilFuncSeparate(), glStencilMask(), glStencilMaskSeparate(), glStencilOp()

                                                    .SH "COPYRIGHT"
                                                        .PP Copyright © 2006 Khronos Group. This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1.0, 8 June 1999. https://opencontent.org/openpub/.

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