This PR adds a WIP timeline UI for animating elements in the scene.
### Implemented Features
* The timeline can be panned with MMB and zoomed with Ctrl + Mouse Wheel
* The timeline can be "scrubbed" by dragging the red "play-head" with
LMB
* The timeline sidebar (displaying the list of tracks) can be resized by
dragging on the edge of the sidebar
* Keyframes can be added by pressing the "Add Keyframe" CTA in the UI
* Keyframes can be selected for editing by clicking the diamond-shaped
markers in the timeline
* Selected entities (including but not limited to keyframes) can be
deleted by pressing the "Delete" key
* Keyframes can be moved temporally by dragging the diamond-shaped
markers in the timeline
### Known issues
* Zooming the timeline in too far results in a soft-lock
* When zooming the timeline, the "transform origin" is currently
centered on the `00:00` timestamp. For ease of use, it should center on
the mouse cursor position instead.
* The timeline track-list is currently hard-coded to list the Camera and
Camera Target. Clicking on these entries currently serves no useful
purpose and may result in a crash.
* Keyframe markers in the timeline are not currently associated with
entries in the track-list and simply appear vertically centered in the
timeline view.
* Added keyframes currently record the position and orientation of the
scene camera when added, and are rendered in the world with debug
visualizations, but serve no useful purpose. Some design work is needed
(both user-experience and architectural) to decide on a workflow for
actually animating scene elements.
* Entity deletion cannot currently be undone/redone
#8 introduced some additional debug information to the view, which was already
rendering some information and visualizations which were not necessary relevant
to the end-user experience. This PR adds an input action (bound to Ctrl + `) to
toggle the display of those visualizations, and disables them by default.
This PR implements basic object selection, with help from `bevy_mod_picking` and
`bevy_mod_outline`.
### Work Done
* Click to select objects in the world
* Selected objects become visually highlighted
* The selected entity is available globally on the `Res<Selection>` resource
* Selected entities can also be queried via the `Selected` marker component
* Pressing `F` will "focus" the camera on the selected entity
* Pressing `Esc` will clear the active selection
### Known Issues
* We're currently using `bevy_mod_picking`'s "Selection" feature, which isn't
aware of our own input events. As a consequence, it will select the object
under the cursor when releasing `LMB` after orbiting the camera, which is not
what we want. This should be pretty easily fixable by dropping
`bevy_mod_picking`'s selection feature and reading the object under the
cursor in our own click listener that only runs if the LMB event is
unhandled.
* The skinned mesh is not currently selectable. This is likely fixable by
adjusting the logic in `scene::mark_scene_objects`... somehow. The `Gltf`
data structure is kind of a nightmare to work with, so this will take some
investigation.
### Future Enhancements
* For parity with other DCC apps, the "Focus" action should also adjust the
camera zoom level to "frame" the selected object in the view. Punting on that
for now because I'm not super confident about the math involved.
* Group selection with Shift/Ctrl and/or marquee selection would be really nice
to have, but probably not critical for now.
Danny McGee