GL_SAMPLEMASK(3G)

💅 NAME

gl_SampleMask — bestie, this one specifies the sample coverage mask for the current fragment ✨

(also hi, you're reading the GL_SAMPLEMASK(3G) page, welcome 🫶)

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🎀 DECLARATION

out int gl_SampleMask[] ;

that's literally it. that's the whole declaration. icon.

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✨ DESCRIPTION

okay so gl_SampleMask is a fragment language output array 🔥 and its whole job is setting the sample mask for the fragment being processed. simple as that.

here's the tea though 👀 — coverage for the current fragment becomes the logical AND of the coverage mask and the output gl_SampleMask. so like, if you set a bit in gl_SampleMask to zero, that corresponding sample gets treated as uncovered for the purposes of multisample fragment operations. bye sample 💀

but listen: setting sample mask bits back to one will never enable samples not covered by the original primitive. that's a one-way street, no take-backs, no cap 🙅‍♀️

the indexing, bestie: bit B of mask gl_SampleMask[M] corresponds to sample 32 * M + B. write that down 📝

this array must be sized in the fragment shader — either implicitly or explicitly — to be the same size as the implementation-dependent maximum sample-mask (as an array of 32-bit elements), determined by the maximum number of samples. okay so it's giving "size it right or perish" 💅

and now the spicy parts 🌶️:

• If the fragment shader statically assigns a value to gl_SampleMask, the sample mask will be undefined for any array elements of any fragment shader invocation that fails to assign a value. (yes, undefined. we don't love that for you 😭)
• If a shader does not statically assign a value to gl_SampleMask, the sample mask has no effect on the processing of a fragment. nothing. zero. it's just vibes.
• If the fragment shader is being evaluated at any frequency other than per-fragment, bits within the sample mask not corresponding to the current fragment shader invocation are ignored. 🙈

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🌈 VERSION SUPPORT

the version support table, but make it a vibe check 👑 — variable name gl_SampleMask, versus OpenGL Shading Language Version:

• 1.10 — - (nope)
• 1.20 — - (nope)
• 1.30 — - (nope)
• 1.40 — - (nope)
• 1.50 — - (nope)
• 3.30 — - (still nope)
• 4.00 — ✔ (ATE 💅)
• 4.10 — ✔
• 4.20 — ✔
• 4.30 — ✔
• 4.40 — ✔
• 4.50 — ✔

so basically 4.00 and onward, she's booked and busy 🦋 periodt.

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🌸 SEE ALSO

go read these next, bestie, they're all in the family 🫶

• gl_SampleMaskIn()
• gl_SampleID()
• gl_SamplePosition()
• gl_FragCoord()

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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/.

💜 COPYRIGHT (again, yes really)

Copyright © 2011-2014 Khronos Group

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🧚 mwah, that's the whole page! it came from [FIXME: source] and it's dated 08/09/2021, so if you're citing it in your essay, that's the receipt 🎀 stay slay, go read gl_SampleMaskIn() next, bye bestie! 💖✨