GLSTENCILOP(3G)

💅 GLSTENCILOP(3G)

okay so this is the GLSTENCILOP(3G) page from the [FIXME: manual] manual, and it’s literally all about <pink>setting front and back stencil test actions</pink> bestie. Stencil energy only. 🎀

✨ NAME ✨

glStencilOp — set front and back stencil test actions. That’s the whole vibe. 🦋

🧚 C SPECIFICATION

void glStencilOp(GLenum sfail, GLenum dpfail, GLenum dppass);

🎀 PARAMETERS

• sfail — tells you what action to take when the stencil test fails. It accepts eight symbolic constants: 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 — tells you 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 — tells you the stencil action when both the stencil test and the depth test pass, or when the stencil test passes and either there’s 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 is like depth-buffering but for enabling and disabling 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. No cap, it’s giving “pixel permission slip.” 💅

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. Main character energy: separate stencil states. 👑

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. 🫶

🌸 The eight stencil actions

• 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 2 n - 1, where n is the value returned by querying GL_STENCIL_BITS. Math era, honestly. 🔥

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. So don’t try to be cute with random enums, bestie. 💀

🔥 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

🌈 VERSION SUPPORT

The version-support table is literally a wall of ✔ and it ate. Function / Feature Name: glStencilOp. OpenGL Version: 2.0 ✔, 2.1 ✔, 3.0 ✔, 3.1 ✔, 3.2 ✔, 3.3 ✔, 4.0 ✔, 4.1 ✔, 4.2 ✔, 4.3 ✔, 4.4 ✔, 4.5 ✔. She’s supported everywhere, periodt. ⭐

👑 SEE ALSO

• glBlendFunc()
• glDepthFunc()
• glEnable()
• glLogicOp()
• glStencilFunc()
• glStencilFuncSeparate()
• glStencilMask()
• glStencilMaskSeparate()
• glStencilOpSeparate()

🫶 COPYRIGHT

Copyright © 1991-2006 Silicon Graphics, Inc. Copyright © 2010-2014 Khronos Group. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/. 💜

🫶 COPYRIGHT

Copyright © 1991-2006 Silicon Graphics, Inc. Copyright © 2010-2014 Khronos Group

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okay bestie, the footer vibes are: source/version [FIXME: source], date 08/09/2021, page GLSTENCILOP(3G) — mwah, slay, and may your stencil tests always pass when you need them to. 💋✨