Create data transmitting class for fgviewer

[show50726]

• Add FrameGraphInfo class for transmitting data between the engine and the server
  • It implements the pimpl pattern
• Adjust DebugServer api to align with the design
  • Has an unique handle to track the views instead of hashing the view name as the key, since the view name is not guaranteed to be unique

[poweifeng]

Sorry I had one more comment that somehow got lost in the shuffle.

Your code has a lot of definitions of this form:

void func(Object copy) {
  value = std::move(copy);
}

I think typically

void func(const Object& obj) {
  value = obj; // actual copy
}

is equivalent and more common.

Or if you're transferring content ownership, then

void func(Object&& obj) {
  value = std::move(obj);
}

is the common pattern.

Any particular reason for choosing that pattern?

[show50726]

My main purpose is to avoid copy since copy vector every frame might be expensive.

According to https://stackoverflow.com/a/51706522,
in my implementation, as long as I call the functions with rvalue type (e.g. func(std::move(obj))), the copy can be avoided since it will call move assignment operator instead.

I think the difference between my impl and transferring content ownership impl you provided is:

• for my impl, you can both pass in rvalue type(no copy) or lvalue type(this will cause a copy)
• for your impl, I will always need to cast the object to rvalue type when calling, or we need to create another method for lvalue type (this will still cause a copy), which might have code repetition

The second one is slightly more optimized, and the first one has simpler codes. I'm okay with both impls. What do you think?

[poweifeng]

My main purpose is to avoid copy since copy vector every frame might be expensive.

According to https://stackoverflow.com/a/51706522, in my implementation, as long as I call the functions with rvalue type (e.g. func(std::move(obj))), the copy can be avoided since it will call move assignment operator instead.

I think the difference between my impl and transferring content ownership impl you provided is:

• for my impl, you can both pass in rvalue type(no copy) or lvalue type(this will cause a copy)
• for your impl, I will always need to cast the object to rvalue type when calling, or we need to create another method for lvalue type (this will still cause a copy), which might have code repetition

The second one is slightly more optimized, and the first one has simpler codes. I'm okay with both impls. What do you think?

I see. I learned something new then. I don't have a strong preference either way. I don't know if Mathias has any thoughts on this or not. Regardless, lgtm!