In C I have the following template:
template<typename UBO>
std::pair<uint, std::vector<std::byte>> SerializeUniform(UBO& ubo, uint binding)
{
// Create raw binary buffers of the uniform data
std::vector<std::byte> ubo_buffer(sizeof(UBO));
memcpy(ubo_buffer.data(), (void*)&ubo, sizeof(UBO));
return {binding, ubo_buffer};
}
inline void SerializeArguments(NECore::UniformBufferDataContainer& data) {}
template<typename T1, typename... Ts>
inline void SerializeArguments(
NECore::UniformBufferDataContainer& data, T1& uniform, uint binding, Ts&... args)
{
data.push_back(SerializeUniform(uniform, binding));
SerializeArguments(data, args...);
}
template<class... Ubos>
void ModuleStorage::Draw(const NECore::RenderRequest& render_request, const Ubos&... args)
{
size_t arg_num = _details::ArgNum(args...);
NECore::UniformBufferDataContainer ubos;
ubos.reserve(arg_num);
_details::SerializeArguments(ubos, args...);
if(render_request.image_outputs.empty())
DrawToScreen(vk_meta_data.vulkan_data, render_request, ubos);
else
DrawOffScreen(vk_meta_data.vulkan_data, render_request, ubos);
}
A bit hard to read so let me walk you through them.
The first template takes a POD and copies it's data into a vector of bytes and then creates a tuple to associate the data with an integer.
The next template is the base case of a recursive template, no parameters, do nothing.
Next we have a recursive template, take the first two parameters, assumed to be a POD and an integer, And serialize the POD. Recurse on the tail.
I.e. this template allows me to serialize an arbitrary number of PODs.
Finally I have a variadic template that allows me to serialize any number of PODs.
You might be wondering why go through all this trouble. It;s so that I can write things like this:
modules.Draw(
{
gltf_shader,
{gallery.GetGpuMeshData(model_names[selected_model])},
textures,
ssbos
},
mvp, 0,
gltf_info, 1);
This way the render command accepts any arbitrary number of uniform parameters which means I can use the same pattern and syntax to call any arbitrary shader my heart desires with any inputs I want (as long as they are byte compatible with the shader declaration)
I am porting this library to rust and I want to achieve a similar thing with macros. i.e. I want to be abble to define things such that I can call
draw(render_request, macro!(ubo1, 0, ubo2, 1))
Or better yet (but I am almost certain this cannot be done in rust)
draw(render_request, ubo1, 0, ubo2, 1)
I am having a very hard time trying to come up with the macro. The primary issue is, macros are not functions and rust doesn't support variadic arguments. I am not entirely sure how to define the macro to achieve what I want.
CodePudding user response:
The usual way will be to define a function that accepts a generic type implementing a trait, and implement the trait (with a macro) for tuples up to X elements.
For example:
pub trait Arguments {
fn serialize(self, ubo: &mut UniformBufferDataContainer);
}
macro_rules! impl_arguments {
(
( $first_generic:ident $($rest_generics:ident)* )
( $first_binding:ident $($rest_bindings:ident)* )
) => {
// Impl for tuples with N elements.
impl_arguments_impl!( ( $first_generic $($rest_generics)* ) ( $first_binding $($rest_bindings)* ) );
// Recurse to impl for tuples with N - 1 and less elements.
impl_arguments!( ( $($rest_generics)* ) ( $($rest_bindings)* ) );
};
// Recursion end condition.
( ( ) ( ) ) => {};
}
macro_rules! impl_arguments_impl {
( ( $($generics:ident) ) ( $($bindings:ident) ) ) => {
impl<$($generics,) > Arguments for ( $( &'_ $generics, u32, ) ) {
fn serialize(self, ubo: &mut UniformBufferDataContainer) {
// Destructure the tuple to access individual arguments.
#[allow(non_snake_case)]
let ( $( $generics, $bindings, ) ) = self;
$(
ubo.push_back(serialize_uniform($generics, $bindings));
)
}
}
};
}
impl_arguments!((H G F E D C B A) (binding8 binding7 binding6 binding5 binding4 binding3 binding2 binding1));
pub fn draw<Ubos: Arguments>(render_request: &mut RenderRequest, args: Ubos) {
// ...
args.serialize(&mut ubos);
// ...
}
Then you call it like:
draw(render_request, (&a, 0, &b, 1));
CodePudding user response:
I managed to get it to work by hacking the vec!
macro from the standard library
macro_rules! UBO {
() => {Vec::<UniformBufferData>::new()};
($($ubo:expr, $binding : expr),* $(,)?) =>
{
[$(serialize_uniform(&$ubo, $binding)), ].to_vec()
}
}
This lets you call the macro UBO!(dummy2, 0, dummy, 1, dummy3, 3)
Which expands into
[
serialize_uniform(&dummy2, 0),
serialize_uniform(&dummy, 1),
serialize_uniform(&dummy3, 3),
]
.to_vec()
So now you can do:
draw(render_request, UBO!(var1, 0, var2, 2, var3, 7));
And it should work (UB and other shennanigans aside).