GLGETSUBROUTINEINDEX(3G)

💅 GLGETSUBROUTINEINDEX — it's giving 3G, bestie

okay so real talk, this one is from the 3G manual section (that's the OpenGL family of manpages, if you didn't know, and now you do 🫶) and it's genuinely such a vibe once you get what it's doing. let's get into it.

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✨ NAME ✨

glGetSubroutineIndex — grab the index of a subroutine uniform, for a specific shader stage, inside a program 🔥

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🎀 C SPECIFICATION 🎀

GLuint glGetSubroutineIndex(GLuint program, GLenum shadertype,
                            const GLchar *name);

like, look at it. three args. so clean. so iconic. 👑

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🦋 PARAMETERS 🦋

• program — the name of the program that's holding your shader stage. this is your "which program tho" answer, bestie.
• shadertype — the shader stage you're querying for a subroutine uniform index. no cap, shadertype has to be one of these five, periodt:
  • GL_VERTEX_SHADER
  • GL_TESS_CONTROL_SHADER
  • GL_TESS_EVALUATION_SHADER
  • GL_GEOMETRY_SHADER
  • GL_FRAGMENT_SHADER
• name — the name of the subroutine uniform whose index you're asking about. yep. that's the whole thing. 🍓

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🌸 DESCRIPTION 🌸

so glGetSubroutineIndex returns the index of a subroutine uniform within a shader stage that's attached to a program object. three bits of lore here:

• program holds the name of the program your shader is attached to.
• shadertype says which stage you're querying the shader subroutine index from.
• name holds the null-terminated name of the subroutine uniform you're querying. 📛

now here's the tea ☕ — if name is not the name of a subroutine uniform in that shader stage, you get GL_INVALID_INDEX back, but no error is generated. like, it just quietly hands you the invalid index and moves on. no drama, no error. 💀

but if name is the name of a subroutine uniform in that shader stage, you get a value between zero and the value of GL_ACTIVE_SUBROUTINES minus one. and the way subroutine indices work: they're assigned using consecutive integers, ranging from zero up to the value of GL_ACTIVE_SUBROUTINES minus one, for that shader stage. so like, no gaps, no weird jumps, just 0, 1, 2, … slay. ✨

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🔥 ERRORS 🔥

• GL_INVALID_ENUM is generated if shadertype or pname is not one of the accepted values. (yes bestie, it literally says pname — there's no pname in this function's signature, but that's what the page says and I'm not about to gaslight the manpage 🙈)
• GL_INVALID_VALUE is generated if program is not the name of an existing program object. so, like, don't pass a fake program name and expect good things. 😭

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👑 VERSION SUPPORT 👑

here's the whole chart, kept exactly as the page has it, because I would never do you dirty like that:

┌──────────────────────┬───────────────────────────────────────────────────────────────────────┐
│                      │                OpenGL Version                                         │
├──────────────────────┼─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┤
│ Function             │ 2.0 │ 2.1 │ 3.0 │ 3.1 │ 3.2 │ 3.3 │ 4.0 │ 4.1 │ 4.2 │ 4.3 │ 4.4 │ 4.5 │
│ /                    │     │     │     │     │     │     │     │     │     │     │     │     │
│ Feature              │     │     │     │     │     │     │     │     │     │     │     │     │
│ Name                 │     │     │     │     │     │     │     │     │     │     │     │     │
├──────────────────────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┤
│ glGetSubroutineIndex │  -  │  -  │  -  │  -  │  -  │  -  │  ✔  │  ✔  │  ✔  │  ✔  │  ✔  │  ✔  │
└──────────────────────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┘

tl;dr: - all the way from 2.0 through 3.3, then ✔ from 4.0 on up to 4.5. she arrived in 4.0 and she's been booked and busy ever since. 💅

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🌈 SEE ALSO 🌈

go read these next, bestie, they're the friend group:

• glGetProgram()
• glGetActiveSubroutineUniform()
• glGetActiveSubroutineUniformName()

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💖 COPYRIGHT 💖

Copyright © 2010-2014 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/.

Copyright © 2010-2014 Khronos Group.

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okay that's the whole page!! 🧚 this one was source [FIXME: source], dated 08/09/2021, and it lives in the 3G manual — so like, cite her correctly when you talk about her. mwah, ily, go write some subroutines 🫶💜