Currently the viewer uses semi-private `EventBus.prototype.{_on, _off}` methods, to try and ensure that all internal viewer state is updated *before* any "external" listeners are invoked.
For all use-cases outside of the viewer, e.g in the integration-tests, the `EventBus.prototype.{on, off}` methods are supposed to be used instead.
Unfortunately this isn't currently enforced in any way, except (hopefully) during review, and generally speaking it's not really possible to prevent the semi-private methods being used (e.g. by third-party users).
Hence this patch adds a new `INTERNAL_EVT` property which is *not* exposed anywhere (neither in the API nor globally), and whose value is generated at build-time, that the viewer uses to mark its `EventBus` listeners are internal.
This allows us to remove the semi-private `EventBus` methods, which helps to simplify that class a little bit.
This patch is adding some code in order to extract a drawing as curves from an image.
The algorithm is basically the following:
- reduce the dimensions
- make it gray
- apply a bilateral filter in order to add some blurryness while keeping the edges
- compute the histogram
- guess what's the background color which should contain a large majority of the pixels
- make a binary image
- extract the contours in using the Suzuki algorithm
- apply the Douglas-Peucker algorithm in order to reduce the number of points
The algorithm is improvable but it should work pretty well if there's a clear difference between
the background and the drawing.
In a v2 we could use a ML model in order to improve the extraction.
There's few changes related to the UI in order to make the tool usable, but they're very basic
for the moment.
When a user deletes any number of annotations, they are notified of the action
by a popup message with an undo button. Besides that, this change reuses the
existing messageBar CSS class from the new alt-text dialog as much as possible.
