Copy / paste entities from the GUI

[chapulina]

Add options to copy / cut / paste models through the GUI.

Hotkeys:

• Cut = CTRL+X
• Copy = CTRL+C
• Paste = CTRL+V

The option should also be available from the context (right-click) menu.

[chapulina]

I'll dump some more things I discussed with @adlarkin here:

The quick way

The quickest approach at the moment would make use of the SpawnFromDescription event and pass the contents of components::ModelSdf (requires #851)

Drawbacks of this approach:

• Only works for models (not lights, actors, etc)
• Requires the GUI to parse the SDF file to create the spawn preview that's attached to the mouse. This can take a non-negligible time for models with multiple links, joints and materials.

The ✨ great ❇️ way

My recommended implementation involves using the clone_name field of msgs::EntityFactory:

1: UserCommands

• Make the UserCommands system parse the clone_name field here:

  https://github.com/ignitionrobotics/ign-gazebo/blob/24be610ac1e8889b6c538a110c84da7f91360a39/src/systems/user_commands/UserCommands.cc#L726-L731

  This would probably entail:

  1. Getting an entity ID from its name
  2. Copying all entities and components that compose this entity
     • Recursively include all children
     • Make sure the new entities have different IDs

  This could be in its own PR. One way to verify that this works would be:

  1. Start ign gazebo shapes.sdf

  2. On another terminal, call:

      ign service -s /world/shapes/create \
          --reqtype ignition.msgs.EntityFactory \
          --reptype ignition.msgs.Boolean \
          --timeout 300 \
         --req 'clone_name: "box", pose {z: 10}, name: "box_copy"'
     

  3. A red box is spawned and falls on top of the original one.

2: 3D Scene

• Create a new SpawnFromCloneName GUI event (or some name like that) that just takes a top-level entity's name. And listen to it from Scene3D.

• Implement the event's behaviour inside Scene3D. Follow the pattern of spawnSdfString / spawnSdfPath:

  https://github.com/ignitionrobotics/ign-gazebo/blob/24be610ac1e8889b6c538a110c84da7f91360a39/src/gui/plugins/scene3d/Scene3D.cc#L217-L222
  Finally
  Unlike those spawning methods though, instead of generating a preview from an SDF file:

  https://github.com/ignitionrobotics/ign-gazebo/blob/24be610ac1e8889b6c538a110c84da7f91360a39/src/gui/plugins/scene3d/Scene3D.cc#L978

  We'll create a new method that generates a preview by copying an existing visual.

• Finally, just add

        else if (!this->dataPtr->spawnCloneName.empty())
        {
           req.set_clone_name(this->dataPtr->spawnCloneName);
        }
  

  here:

  https://github.com/ignitionrobotics/ign-gazebo/blob/24be610ac1e8889b6c538a110c84da7f91360a39/src/gui/plugins/scene3d/Scene3D.cc#L1343-L1355

3: New copy / paste plugin

• Create a new GUI plugin that calls the SpawnFromCloneName when the user requests it