Different function calls for different Conditions

[AaronBeardless]

Current Setup

I´ve got a simple Renderer which has 2 "Draw"-functions
Draw1 takes only a mesh as an argument and renders it with a default material
Draw2 takes a mesh and a material as an argument and renders it.
(The function are both called Draw in the actual program, but for the sake of clarity I decided to call them Draw1 and Draw2)

Problem

Using the second function works just fine, I use a "view" to get both components and pass them onto the function.
The problem is I don´t know how check for just one component and then for the other.

It would (in theory) work like this:

1. Check if entity has a mesh component
2. Check if entity has a material component
3. If an entity only has a mesh component, use Draw1
4. If an entity has both components, use Draw2

How could I achieve that with ENTT?

[codylico]

Maybe you could use a view that gives both entity identifier and mesh component, then try to look up the material by entity identifier? I'm not sure if and how that would work, though; maybe someone else can verify.

[Green-Sky]

basically. Use a view with all common components (mesh component) and inside the iteration check for conditional components (material).
Since you are provided with the entity(id) you can just if (registry.all_of<material_component>(entity)) {} else {}.

[Green-Sky]

There is an option to exclude specific components from a view, but I am not sure how much slower 2 separate view would be.

[skypjack]

If I get it correctly, this is what you're looking for?

for(auto [entity, cmesh]: registry.view<mesh>(entt::exclude<material>).each()) { Draw1(cmesh); } // (1)
for(auto [entity, cmesh, cmaterial]: registry.view<mesh, material>().each()) { Draw2(cmesh. cmaterial); } // (2)

That is:

1. If an entity only has a mesh component, use Draw1 (and therefore it has not material component)
2. If an entity has both components, use Draw2

[AaronBeardless]

Oh god, I can´t believe it is that simple, now I feel stupid!
Nevertheless: Thank you!

[skypjack]

You're welcome. 🙂

[codylico]

The following is an idea I came up with:

Maybe use a view that gives both entity and mesh component, then try to look up the material by entity ID? Someone else can confirm whether that works....

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Message ID: ***@***.***>

[skypjack]

Yeah, it also works. It's mostly a matter of tastes I guess.