Automate mesh description via a macro

[gfx-rs]

Automate mesh description via a macro

[kvark]

Code to derive a field offset by @Kimundi:

struct Foo { bar: uint, baz: uint }
unsafe { &(*(0u as *const Foo)).baz as *const _ as uint }

Macro version:

macro_rules! offset_of { ($t:ty, $i:ident) => {unsafe { &(*(0u as *const $t)).$i as *const _ as uint }}}
struct Foo { bar: uint, baz: uint } offset_of!(Foo, baz)

Finally, the stride can be (obviously) extracted by std::mem::size_of::<T>()
The size of the attribute (number of components) should be possible to extract from the fixed-size array definition. Hence, everything seems to be ready for a macro to write.

[brendanzab]

What is the definition of Format in fn get_format() -> Format;?

[kvark]

@bjz Format might be as simple as Vec<mesh::Attribute>

[kvark]

After implementing shader_param attribute, this one is going to be fairly trivial for me.

[kvark]

Fixed by #122