vulkan: replacing @embedfile shaders with runtime known shaders | Zig Programming Language | Page 1

plain silo Mar 31, 2025, 7:30 PM

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Hi, sorry for the bad title, couldn't think of a good one.

im having trouble, im trying to replace @embedfile with runtime known code, that way i don't have to recompile every time i change shader code.

    var shader_modules: [2]vk.ShaderModule = undefined;
    for (shader_paths, 0..) |s, i| {
        const shader_file = try std.fs.cwd().openFile(s, .{});
        defer shader_file.close();

        const spirv: []u8 align(@alignOf(u32)) = try allocator.alloc(u8, try shader_file.getEndPos());
        defer allocator.free(spirv);
        const shader_len = try shader_file.readAll(spirv);

        std.debug.assert(shader_len == spirv.len);

        const shader_mod = try gc.dev.createShaderModule(&.{
            .code_size = spirv.len,
            .p_code = @ptrCast(&spirv),
        }, null);
        shader_modules[i] = shader_mod;
    }

    defer gc.dev.destroyShaderModule(shader_modules[0], null);
    defer gc.dev.destroyShaderModule(shader_modules[1], null);

this code is for a vulkan shader module, the problem is, it expects a ?[*]const u32 array, but due to alignemnt or some other reason. the SPIRV code seems to be wrong.

readall expects a []u8, so i can't supply it with a []u32, i tried aligning as you see in the code, but it doesn't work either.

this is the vulkan error, although im not sure if it'll be much of help

VUID-VkShaderModuleCreateInfo-pCode-07912(ERROR / SPEC): msgNum: 979894520 - Validation Error: [ VUID-VkShaderModuleCreateInfo-pCode-07912 ] | MessageID = 0x3a6800f8 | vkCreateShaderModule(): pCreateInfo->pCode doesn't point to a SPIR-V module. The Vulkan spec states: If the VK_NV_glsl_shader extension is not enabled, pCode must be a pointer to SPIR-V code (https://www.khronos.org/registry/vulkan/specs/1.3-extensions/html/vkspec.html#VUID-VkShaderModuleCreateInfo-pCode-07912)
    Objects: 0

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previously, the code worked just fine with just

const vert_spv align(@alignOf(u32)) = @embedFile("../shaders/vert.spv").*;
const frag_spv align(@alignOf(u32)) = @embedFile("../shaders/frag.spv").*;

but as i said, i want to move away from comptime known files.

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vulkan: replacing @embedfile shaders with runtime known shaders

acoustic barn Mar 31, 2025, 7:38 PM

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are the files "../shaders/vert.spv"... supposed to be utf8 source or bytecode? why is the u32 alignment needed?

plain silo Mar 31, 2025, 7:41 PM

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bytecode

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u32 is needed because uhh...yes, the vulkan-zig guide had the files embeded while aligned.
which i assume because vulkan expects an array of u32

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to be clear, .spv files are shader files compiled to SPIRV.

acoustic barn Mar 31, 2025, 7:43 PM

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uh huh. where are these files gotten from?

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does the build script compile them from some source?

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there's a function alignedAlloc you may want to look into

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pass the alignment of u32 in

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also, what's the thing that requires a ?[*]const u32?

plain silo Mar 31, 2025, 7:46 PM

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acoustic barn uh huh. where are these files gotten from?

its from a shader compiler. i verified the compiled shaders work by using @embedFile

acoustic barn Mar 31, 2025, 7:46 PM

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oh ok

plain silo Mar 31, 2025, 7:46 PM

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acoustic barn also, what's the thing that requires a `?[*]const u32`?

in order to create a vulkan shader module, you need a pointer to SPIRV array code

acoustic barn Mar 31, 2025, 7:47 PM

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oh i see

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so what's your current problem right now

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&spirv is going to be *const []u8 if i am not mistaken here (before being casted)

plain silo Mar 31, 2025, 7:48 PM

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i must've done the alignment wrong or the array setup wrong because vulkan throws an error that the compiled shader code is wrong

acoustic barn Mar 31, 2025, 7:48 PM

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did you try alignedAlloc as i pointed out?

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does it give the same error

plain silo Mar 31, 2025, 7:49 PM

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yep

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const spirv: []u8 align(@alignOf(u32)) = try allocator.alignedAlloc(u8, @alignOf(u32), try shader_file.getEndPos());
        defer allocator.free(spirv);
        const shader_len = try shader_file.readAll(spirv);

here's what i changed

acoustic barn Mar 31, 2025, 7:50 PM

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plain silo Hi, sorry for the bad title, couldn't think of a good one. im having trouble, i...

if there's more stacktrace than just that, it'd be helpful
this error is printed when you call gc.dev.createShaderModule, right?

plain silo Mar 31, 2025, 7:53 PM

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yep

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VUID-VkShaderModuleCreateInfo-pCode-07912(ERROR / SPEC): msgNum: 979894520 - Validation Error: [ VUID-VkShaderModuleCreateInfo-pCode-07912 ] | MessageID = 0x3a6800f8 | vkCreateShaderModule(): pCreateInfo->pCode doesn't point to a SPIR-V module. The Vulkan spec states: If the VK_NV_glsl_shader extension is not enabled, pCode must be a pointer to SPIR-V code (https://www.khronos.org/registry/vulkan/specs/1.3-extensions/html/vkspec.html#VUID-VkShaderModuleCreateInfo-pCode-07912)
    Objects: 0
VUID-VkShaderModuleCreateInfo-pCode-08737(ERROR / SPEC): msgNum: -1520283006 - Validation Error: [ VUID-VkShaderModuleCreateInfo-pCode-08737 ] | MessageID = 0xa5625282 | vkCreateShaderModule(): pCreateInfo->pCode (spirv-val produced an error):
Invalid SPIR-V magic number. The Vulkan spec states: If pCode is a pointer to SPIR-V code, pCode must adhere to the validation rules described by the Validation Rules within a Module section of the SPIR-V Environment appendix (https://www.khronos.org/registry/vulkan/specs/1.3-extensions/html/vkspec.html#VUID-VkShaderModuleCreateInfo-pCode-08737)
    Objects: 0

it's just the same two errors

acoustic barn Mar 31, 2025, 7:54 PM

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can you assert that @ptrCast(&spirv) is of type ?[*]const u32 by refactoring it into a separate value?

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aka.

const intermediatry_ptr: ?[*]const u32 = @ptrCast(&spirv);

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because what i feel is happening here is &spirv makes a pointer to the stack value where the spirv value lives

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and when you pointer cast it, it just reads the slice and past it

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you may need to remove that & in front of the spirv

plain silo Mar 31, 2025, 7:58 PM

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acoustic barn because what i feel is happening here is `&spirv` makes a pointer to the stack v...

bingo

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that was it!

acoustic barn Mar 31, 2025, 7:59 PM

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im glad that i could be of help

plain silo Mar 31, 2025, 7:59 PM

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thank you very much

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i had a feeling it was ptrCast, but no way i would've guessed its a stack pointer

acoustic barn Mar 31, 2025, 8:00 PM

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yeah spirv itself is already []u8

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which is something like a ptr + length struct

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you'll read at most 4 u32's out of that value

#vulkan: replacing @embedfile shaders with runtime known shaders