GL_INVOCATIONID(3G)

💅 GL_INVOCATIONID (3G) — the manual page, but make it make sense

okay bestie, so this is the manual page for gl_InvocationID — it lives in the OpenGL Shading Language docs (the header literally says [FIXME: manual], which is giving "we'll fix it later, and later never came" 😭). Anyway, it's short, it's iconic, let's go 🫶

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✨ NAME ✨

gl_InvocationID — it's the variable that holds the invocation index of whatever shader invocation is currently running, no cap 👑

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🎀 DECLARATION 🎀

Here's the literal declaration, exactly as written, don't touch it:

in int gl_InvocationID ;

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💖 DESCRIPTION 💖

So the whole personality of this variable changes depending on which shader language you're in. Two vibes, one variable:

🧚 In the tessellation control language

gl_InvocationID holds the index of the output patch vertex that got assigned to the shader invocation. It's handed an integer value in the range [0, N-1], where N is the number of output patch vertices.

🦋 In the geometry language

gl_InvocationID identifies the invocation number that got assigned to the geometry shader invocation. It's handed an integer value in the range [0, N-1], where N is the number of geometry shader invocations per primitive.

TL;DR: same <pink>int variable name, two completely different job descriptions depending on where you're standing. lowkey iconic ✨

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🌈 VERSION SUPPORT 🌈

Here's the vibe check across every OpenGL Shading Language version — ✔ means it's there, - means she has not arrived yet 💀

• Variable name: gl_InvocationID
  • 1.10 — -
  • 1.20 — -
  • 1.30 — -
  • 1.40 — -
  • 1.50 — ✔
  • 3.30 — ✔
  • 4.00 — ✔
  • 4.10 — ✔
  • 4.20 — ✔
  • 4.30 — ✔
  • 4.40 — ✔
  • 4.50 — ✔

[1] Versions 1.50 to 3.30 — geometry shaders only. so clock that 📌 she was exclusive before she went mainstream, iykyk

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👀 SEE ALSO 👀

Go give these a look too, they're in the same friend group:

• gl_InstanceID()

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💜 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/.

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💜 COPYRIGHT (yes, again 💀) 💜

Copyright © 2011-2014 Khronos Group

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okay that's the whole page, you ate that 🍓 fr fr. quick cute sign-off: this masterpiece is sourced from [FIXME: source], dated 08/09/2021, and it's GL_INVOCATIONID(3G) all the way down. mwah 💋✨