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We must not use vectors in extern structs #1634
Description
They don't have a guaranteed memory layout, see ziglang/zig#24179 (comment)
this is a requirement for #1583
Problematic places:
-
QuadInfoinmodels.zig -
ChunkDatainchunk_meshing.zig -
Particleinparticles.zig(this one is even missing the extern declaration)
I think the best solution for now is probably just to use e.g. align(16) [3]f32 instead of Vec3f and coerce them in all use-cases
Activity
jingkaimori commentedon Jun 19, 2025
could zig make some optimization by altering layout of vector? if so, only vectors passed into pipeline should be changed to aligned fix-width array.
IntegratedQuantum commentedon Jun 19, 2025
This is only about extern structs, which are used to communicate with e.g. glsl, where we must, at all cost, have a fixed memory layout.
jingkaimori commentedon Jun 19, 2025
It seems like most vector is decomposed like here before passing into glsl:
Cubyz/src/renderer.zig
Lines 314 to 315 in 9c33f81
However, vectors could be passed in as a pointer to aligned buffer:
Cubyz/src/renderer/chunk_meshing.zig
Line 213 in 9c33f81
Therefore only some vector should be changed to given layout, which is passed into APIs ending with a
vlikeglUniformxxvIntegratedQuantum commentedon Jun 19, 2025
Again, this is only about extern structs, as far as I'm aware you can still safely
@ptrCastfrom a vector to an array pointer, so there is no problem with theglUniformcalls.Don't use vector types in the GPU buffer.
Make particle struct extern (#2066)
Make particle struct extern (PixelGuys#2066)
Make particle struct extern (PixelGuys#2066)