Cody Spahr

There is a work around where you can use the Mesh Paint Mode(Shift+4) inside unreal, and paint vertex colours. Then in the HDA, convert the vertex vector data to do what you need.

Example, you can do an attribute promote to turn the @Cd from Vertices to Points. use a wrangle to convert the red to a density float attribute. Then you can use a Scatter SOP with Density. So the resulting HDA can let you paint RED to scatter objects on a static mesh in Unreal.

This would give very similar tool to the attribute paint sop.

Houdini Engine can not run HDAs at real time. It is all done on the construction side(since it requires Houdini for cooking). That being said, you can use HDAs to build these unique user interactions content with HDAs, and enable them through blueprints. For example, you could animate the effects of a bulge with vertex animated textures, or baking morph targets into the fbx(Although I am not sure that is supported in UE5). And you can create that content with HDAs in the editor. And use blueprints to give the user control over its strength.