Would there be a way to "attach" actors (i.e bind their coordinates) so as to have gamesalad automatically implement their drag and density on each other?
Not easily, it's fairly straightforward to attach two objects together, but getting them to effect each other's physics is a mathematical mountain to climb !
You could do this with polygonal/custom physics shapes, they are planned for GameSalad, but there unlikely to be here any time soon.
If you were just after a simple summing of two actor's 'drag' or 'density' values you could do that, but if you then want the conjoined actor to interact with other actors (to collide with and otherwise detect) things get very very tricky very quickly !
Here are a bunch of separate actors that have been joined together (file attached) - like I say although the joining of separate actors into one is not too hard you can't easily do stuff like have the 'child' actors collide with other actors while they are attached to the parent object.
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If you were just after a simple summing of two actor's 'drag' or 'density' values you could do that, but if you then want the conjoined actor to interact with other actors (to collide with and otherwise detect) things get very very tricky very quickly !