Setting color and transparency_group for all entities in model

[FredrikNoren]

We currently have outline_recursive, which will apply the outline to all child entities. We could do something similar (color_recursive and transparency_group_recursive). Or we could try to figure out some more general solution to this.

[philpax]

entity::set_component_recursive or entity::set_component_for_hierarchy maybe?

[FredrikNoren]

@philpax Well the user would then have to somehow wait until the model is loaded and then run those.

[philpax]

Hm, good point... we probably want a way of detecting that as well, but I'm not sure when it would fire (like how do you say loading is "done" if the user can keep attaching components to it to load more things?)

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In the meantime I'm fine with transparency_group_recursive, we can figure out a more general solution later

[droqen]

Made a discussion about two-entity queries which could be the form of a possible 'more general solution': #600