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.
- it's now possible to start a drawing with a pen and use fingers to zoom
or scroll without interacting with the current drawing;
- it's now possible to draw with a finger and them zoom with two fingers.
This patch makes a clear separation between the way to draw and the editing stuff.
It adds a class DrawEditor which should be extended in order to create new drawing tools.
As an example, the ink tool has been rewritten in order to use it.
When playing with a pen, I noticed that sometimes a free highlight has still its
gray outline when an other one is drawn: for any reason the pointerleave event isn't
triggered.
The idea is to insert a span in the text layer with an aria-role set to img
and use the bounding box provided by the attribute field in the tag dict in
order to have non-null dimensions for the image to make it "visible".
There's a fair number of event listeners in the editor-code that we're currently removing "manually", by keeping references to their event handler functions.
This was necessary since we have a "global" `AbortController` that applies to all event listeners used in the editor-code, however it's now possible to combine multiple `AbortSignal`s; please see https://developer.mozilla.org/en-US/docs/Web/API/AbortSignal/any_static
Since this functionality is [fairly new](https://developer.mozilla.org/en-US/docs/Web/API/AbortSignal/any_static#browser_compatibility) the viewer will check that `AbortSignal.any()` is available before enabling the editing-functionality.
(It should hopefully be fairly straightforward, famous last words, for users to implement a polyfill to allow editing in older browsers.)
Finally, this patch also adds checks and test-only asserts to ensure that we don't add duplicate event listeners in various editor-code.
When the mouse was hovering an existing highlight, all the text in the page
was selected.
So when the user is selecting some text or drawing a free highlight, the mouse
is disabled for the existing editors.
The original bug was because the parent was null when trying to show
an highlight annotation which led to an exception.
That led me to think about having some null/non-null parent when removing
an editor: it's a mess especially if a destroyed parent is still attached
to an editor. Consequently, this patch always sets the parent to null when
deleting the editor.
In implementing caret browsing mode in pdf.js, I didn't notice that selectstart isn't always triggered.
So this patch removes the use of selectstart and rely only on selectionchange.
In order to simplify the selection management, the selection code is moved in the AnnotationUIManager:
- it simplifies the code;
- it allows to have only one listener for selectionchange instead of having one by visible page
for selectstart.
I had to add a delay in the integration tests for highlighting (there's a comment with an explanation),
it isn't really nice, but it's the only way I found and in real life there always is a delay between
press and release.
When highlighting, the annotation editor layer is disabled to get pointer events
from the text layer, but the annotation layer must be then disabled either in
order to avoid bad interactions.
The free highlighting is enabled when the mouse pointer isn't on some text.
Then we draw a shape with smoothed borders corresponding to the movement of
the mouse.
Printing/saving and changing the thickness will come later.
When the editor is invisible (because on a non-rendered page) its parent is null.
But when we undo its deletion, we need to have a parent to attach it.
This fixes invalid type references (either due to invalid paths for the
import or missing imports) in the JS doc, as well as some missing or
invalid parameter names for @param annotations.
