Question how to set only some values of a component?

Let's say I'm trying to spawn a bunch of enemies,

I created an entity command buffer and use it to instantiate my enemy.

Entity enemy = ecb.Instantiate(enemyPrefab);

then I need to set the enemy's spawn position so I'll need to call setcomponent()

ecb.SetComponent(enemy, new LocalTransform(){...})

The problem is the way we set component is basically creating a new component and replace it with the old one ( it seems, I'm not certain)

In this case, I only care about setting position data, but not the whole LocalTransform, for example the scale is set in the inspector and I don't want to touch it.

Or maybe I'm totally wrong? setcomponent() will compare and only set data that's different? so there's no need to worry at all

 

Correct. SetComponent = replace entirely.

 

- Store initial transform or values (e.g. during baking);
- Use a copy of initial data during initialization;
- Modify position
- Apply the whole struct.

Alternatively, you could also read data directly from the prefab entity.
But that should be slower in theory depending on the numbers.

 

Thanks, looks like we shouldn't have too much data packed in one component, otherwise it would a pain to call setcomopnent

 

Ideally, it shouldn't matter, since structural changes should be used rarely.
But when it happens, well its a bit more typing. Its not that bad though.

Since all components are structs, you'd just copy the whole thing in one go, then apply diff.
It takes less code than to describe what is required to be done. E.g.

Code (CSharp):

1. T someData = initialData;
2. someData.Position = value;
3.  
4. ecb.SetComponent(entity, someData);

As for the prefab related data. You'd want some kind of "settings" that have a prefab inside it.
So storing required extra values / settings shouldn't be a big deal.

 

1. In your spawn system, read LocalTransform from the prefab and store in local variable.
2. Change Position on that LocalTransform local variable
3. Call SetComponent on ECB with that LocalTransform.