GL_FRONTFACING(3G)

💅 GL_FRONTFACING 💅

okay so bestie, this is the GL_FRONTFACING(3G) page — yes, 3G is the manual name, and the header lowkey also says [FIXME: manual], so we're working with what we've got 💖. It's all about whether a primitive is front or back facing, and it's honestly giving graphics-pipeline main character energy ✨.

✨ NAME ✨

gl_FrontFacing — indicates whether a primitive is front or back facing. That's the whole vibe of the name, no cap 💅.

🎀 DECLARATION 🎀

in bool gl_FrontFacing ;.SH "DESCRIPTION"

bestie, that stray .SH "DESCRIPTION" is literally glued onto the declaration in the source, and I am not editing it, because facts are facts 🫶.

💖 DESCRIPTION 💖

Available only in the fragment language, gl_FrontFacing is an input variable whose value is true if the fragment belongs to a front-facing primitive and false otherwise. slay, that's the whole point 🔥.

The determination of whether a triangle primitive is front-facing is made by examining the sign of the area of the triangle, including a possible reversal of this sign as controlled by glFrontFace. One way to compute this area is:

a=12 ∑ j=0 n-1 x w i y w i+1 - x w i+1 y w i

where x w i and y w i are the x and y window coordinates of the ith vertex of the n-vertex polygon. keep that exactly as-is, bestie, character for character 💀.

The sign of this computation is negated when the value of GL_CLIP_ORIGIN (the clip volume origin, set with glClipControl()) is GL_UPPER_LEFT. so yeah, flip the vibe when the clip origin is upper-left 🌈.

🌈 VERSION SUPPORT 🌈

Variable name: gl_FrontFacing

OpenGL Shading Language Version — gl_FrontFacing is supported with ✔ in every version listed:

• 1.10 — ✔
• 1.20 — ✔
• 1.30 — ✔
• 1.40 — ✔
• 1.50 — ✔
• 3.30 — ✔
• 4.00 — ✔
• 4.10 — ✔
• 4.20 — ✔
• 4.30 — ✔
• 4.40 — ✔
• 4.50 — ✔

🦋 SEE ALSO 🦋

• gl_FragCoord()
• glClipControl()

👑 COPYRIGHT 👑

Copyright © 2011-2014 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/. periodt 💅.

👑 COPYRIGHT 👑

Copyright © 2011-2014 Khronos Group. yeah bestie, that's the short one, and we're keeping it too 🎀.

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signed off with [FIXME: source], dated 08/09/2021, and stamped GL_FRONTFACING(3G) — mwah 💋✨