GLSTENCILOPSEPARATE(3G)

📦
version 1.1 · 7 versions
, in centos-stream 9

💅 GLSTENCILOPSEPARATE 💅

okay so bestie, this is the glStencilOpSeparate page from the OpenGL manual (that's the 3G bit, iykyk) — and it's literally the one that lets your front faces and your back faces have totally different stencil opinions. main character energy fr fr.

✨ NAME ✨

glStencilOpSeparate — set front and/or back stencil test actions 🎀

🧚 C SPECIFICATION 🧚

void glStencilOpSeparate(GLenum face, GLenum sfail, GLenum dpfail,
                         GLenum dppass);

🌸 PARAMETERS 🌸

  • face — tells the driver whether you're updating the front stencil state, the back stencil state, or both. Only three symbolic constants are valid here: GL_FRONT, GL_BACK, and GL_FRONT_AND_BACK.
  • sfail — 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 — the stencil action for 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 — the stencil action for when both the stencil test and the depth test pass, or when the stencil test passes and there's either no depth buffer or depth testing isn't 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. it's giving arts-and-crafts but make it pixels 🎨✨

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, as if glStencilOpSeparate() were called with face set to GL_FRONT_AND_BACK. so like, glStencilOp is the "no thoughts head empty, same vibe both sides" version 💀

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 👇

  • 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.

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. so dpfail is just sitting there with nothing to do, poor thing 🫶

🌈 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 test always passes. iconic "fake it till you make it" behaviour honestly ✨

💀 ERRORS 💀

  • GL_INVALID_ENUM is generated if face is any value other than GL_FRONT, GL_BACK, or GL_FRONT_AND_BACK.
  • GL_INVALID_ENUM is generated if sfail, dpfail, or dppass is any value other than the eight defined constant values.
bestie do NOT pass random ints here, the driver will simply hand you a GL_INVALID_ENUM and walk away 😭

🦋 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 original does this whole table thing, but tables aren't allowed here so — list edition, same facts, no cap 💅)

The function/feature name is glStencilOpSeparate, and it's got a ✔ in every single OpenGL version column listed:

  • OpenGL 2.0 — ✔
  • OpenGL 2.1 — ✔
  • OpenGL 3.0 — ✔
  • OpenGL 3.1 — ✔
  • OpenGL 3.2 — ✔
  • OpenGL 3.3 — ✔
  • OpenGL 4.0 — ✔
  • OpenGL 4.1 — ✔
  • OpenGL 4.2 — ✔
  • OpenGL 4.3 — ✔
  • OpenGL 4.4 — ✔
  • OpenGL 4.5 — ✔

ate and left zero crumbs, every version, all checkmarks 🔥

🍓 SEE ALSO 🍓

glBlendFunc(), glDepthFunc(), glEnable(), glLogicOp(), glStencilFunc(), glStencilFuncSeparate(), glStencilMask(), glStencilMaskSeparate(), glStencilOp()

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. http://opencontent.org/openpub/.

Copyright © 1991-2006 Silicon Graphics, Inc.

okay that's the whole page bestie, go stencil something gorgeous 🌟

sign-off tea ☕: this page came from the [FIXME: source] vibes with a date of 08/09/2021, and it's GLSTENCILOPSEPARATE(3G) all the way through — mwah, bye 💋

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