Fix shader uniforms has null as default value

[Chaosus]

• Closes Shader uniforms has null as default value #44454

[akien-mga]

TL;DR: I looked into how to improve this code myself but in the end I gave up.

I was still wondering if there isn't a simpler way to do this. There must exist a pre-existing method in the codebase to construct a Variant with a given type and default initialize it.

From a quick look, I found:

void Variant::construct(Variant::Type p_type, Variant &base, const Variant **p_args, int p_argcount, Callable::CallError &r_error);

Which I think you would use like this:

Callable::CallError ce;
Variant value;
Variant::construct(variant_type, value, nullptr, 0, ce);

This would allow to simplify the cases quite a bit, like (untested):

switch (p_type) {
	case ShaderLanguage::TYPE_BOOL:
		if (array_size > 0) {
			type = Variant::PACKED_INT32_ARRAY;
		} else {
			type = Variant::BOOL;
		}
		break;
	case ShaderLanguage::TYPE_BVEC2:
		if (array_size > 0) {
			type = Variant::PACKED_INT32_ARRAY;
			array_size *= 2;
		} else {
			type = Variant::INT;
		}
		break;
	...
	}
}

Callable::CallError ce;
Variant value;
Variant::construct(variant_type, value, nullptr, 0, ce);

if (array_size > 0) {
	// Figure out a way to resize the array in Variant and `zero()` it.
}

But I finally noticed that this is pretty much adapted from ShaderLanguage::constant_value_to_variant and so keeping a consistent format might be worth it. The type conversions are also less trivial than I thought with types not natively compatible with Variant like bvec2.

And so at this point I gave up on trying to make this better :P

[akien-mga]

Would be worth a rebase before merging as this is fairly old.

[Chaosus]

@akien-mga Done

[Repiteo]

Thanks!