The Linux graphics stack in a nutshell, part 1

The Linux graphics stack in a nutshell, part 1

Posted Dec 20, 2023 4:01 UTC (Wed) by tshow (subscriber, #6411)
In reply to: The Linux graphics stack in a nutshell, part 1 by adobriyan
Parent article: The Linux graphics stack in a nutshell, part 1

> For those who are going to try Vulkan: it takes like 1000 LOC in C to hello world a triangle from scratch. Add few hundred LOC more for a textured triangle.

Vulkan is very verbose, but a lot of this can be mitigated with some macro magic if you're using relatively recent C (and if you're building for Vulkan, why wouldn't you be?). There's a bunch of pure boilerplate you can macro away.

In particular, a lot of the functions take pointers to structures as arguments. This means you wind up doing a lot of:

vkCreateFoo(&(VkFooCreateInfo)
    {
      .sType  = VK_STRUCTURE_TYPE_FOO,
      .thing  = VK_TRUE,
      .answer = 42
    });

In my game engine I've got #defines of the form:

#define STVK(_name, _type) &(Vk##_name) { .sType = VK_STRUCTURE_TYPE_##_type
#define ARG_VkFooCreateInfo(...) STVK(FooCreateInfo, FOO_CREATE_INFO), __VA_ARGS__ }

The above could be done without the STVK() macro by expanding it inline in the ARG_ macro, but unless you're going to autogenerate the macros (say, with a ruby script that greps vulkan_core.h for VK_STRUCTURE_TYPE...) it's less prolix to have the helper macro.

With that, the call becomes:

vkCreateFoo(ARG_VkFooCreateInfo(.thing = VK_TRUE, .answer = 42));

or if you like maximal vertical spread:

vkCreateFoo(
  ARG_VkFooCreateInfo(
    .thing  = VK_TRUE,
    .answer = 42
  )
);

I'm simplifying a bit (most vulkan calls want an allocator pointer, for instance, though you can probably macro that away too unless you plan to use different allocators in different places), but the macro scheme above gets rid of a lot of the boilerplate and makes the code a lot easier to read, IMO. Particularly when you get to things like vkCreateGraphicsPipeline() which takes very large structures.

There's a lot of other places you can do that as well. For example, are you planning to have custom names for your shader entry points? If not, you can macro .pName = "main" into all your VkPipelineShaderStageCreateInfo structures.

You can also clean things up a lot by remembering that when you init a structure inline in C, all members not explicitly mentioned are zeroed, so if you have any lines like .flags = 0, (hint: you do; there are a lot of flag fields with no flags defined yet in Vulkan...) you can get rid of them unless you think it's needed for clarity.

Being low level, Vulkan gives you a lot of flexibility you'll probably never use. Nailing down the bits you won't care about in macros behind the scenes makes it much simpler to work with, though I obviously advise heavily documenting your macros wherever they live in case your assumptions change.

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