## Camera Manipulation (Flutter)

> You can find the entire project below in the [flutter/quickstart](https://github.com/nmfisher/thermion/examples/flutter/camera_manipulation) folder.

A `ThermionListenerWidget` is one option for manipulating the camera with an input device (e.g. mouse or touchscreen gestures). 

This will generally wrap a `ThermionWidget`, meaning the entire viewport will act as a receiver for gesture events. 

> You can position this independently (for example, stacked vertically beneath the viewport), but this will not translate picking queries correctly.

```
@override
  Widget build(BuildContext context) {
    return Stack(children: [
      if (_thermionViewer != null)
        Positioned.fill(
            child: ThermionListenerWidget(
                inputHandler:
                    DelegateInputHandler.fixedOrbit(_thermionViewer!)
                    ..setActionForType(InputType.MMB_HOLD_AND_MOVE, InputAction.ROTATE)
                    ..setActionForType(InputType.SCALE1, InputAction.ROTATE)
                    ..setActionForType(InputType.SCALE2, InputAction.ZOOM)
                    ..setActionForType(InputType.SCROLLWHEEL, InputAction.ZOOM),
                child: ThermionWidget(
                  viewer: _thermionViewer!,
                ))),
    ]);
```

`ThermionListenerWidget` is a very simple widget; it simply forwards pointer, gesture and keyboard events to the provided [InputHandler], which must decide how to interpret those events.

For example, one [InputHandler] implementation might interpret mouse pointer movement as "rotate the camera", whereas a separate implementation might interpret it as "translate this specific entity".

Thermion provides two default InputHandler implementations for manipulating the camera: [DelegateInputHandler.fixedOrbit] and [DelegateInputHandler.flight].

[DelegateInputHandler.fixedOrbit] will rotate the camera in a fixed orbit around a target point (the origin, by default), and also allow zooming in/out (subject to a minimum distance, which is configurable).

By default, [DelegateInputHandler.fixedOrbit] will:
- rotate the camera when the middle mouse button is held and the pointer is moved (on desktop), and when a single swipe left/right/up/down is detected (on mobile)
- zoom the camera when the scroll wheel is scrolled up/down (on desktop), and when a pinch gesture is detected (on mobile)

You can change the action for a specific input type by calling `setActionForType`; for example, if you wanted to rotate the camera by moving the mouse pointer while holding the left mouse button, you would call:

```
setActionForType(InputType.LMB_HOLD_AND_MOVE, InputAction.ROTATE)
```

See the [InputType] and [InputAction] enums for available input types and actions.

[DelegateInputHandler.flight] will translate keyboard and mouse/touchscreen gestures to free flight camera manipulation. 

By default:
- holding the middle mouse button will control the pitch/roll/yaw of the camera
- holding the left mouse button will pan the camera left/right/up/down
- the middle mouse button will zoom/dolly the camera in/out
- the WASD keys will pan the camera left/right/up/down and dolly the camera forward/backward

If these don't exactly fit your use case, you can create your own [InputHandler] implementation. If you think it would be useful to other users, please feel free to submit a PR for your implementation to be included in the base Thermion package.





