Improve the Path tool's segment editing mode

[4adex]

Closes #2832

[Keavon]

• Two more issues in this video. First part shows being able to hover a point even if it's invisible. Second part shows how the new hover styling (which I updated the visuals of) turns white when it's already selected, but should only apply the visual change to the outside while keeping the inner part solid blue because it's still selected.

  capture_34_.mp4
  • We also want the anchors/handles to light up, as if hovered, when currently within the box/lasso selection. And segments while in segment mode.

• Shift clicking the point/segment mode checkboxes still lets you deselect all of them, but deselecting all shouldn't be possible.

• If I have a segment selected in segment mode, switching to point mode keeps that segment selected which shouldn't be possible.

• Upon inserting a point, it needs to not select the point, while in segment mode, since point selection shouldn't ever occur in that mode.

[4adex]

#2860 (comment)
All of these are also covered in this PR, double checked.

[Keavon]

Can you please explain the idea behind the frozen flag in the CheckboxInput, why that's necessary (what consideration was taken for doing it purely in the backend?), etc.?

[4adex]

I first did it purely in backend only, so these were the two approaches that I tried -

• I used the disabled flag (disabled when only one mode is activated) so that you cannot turn both modes to false, as in https://130b5a88.graphite.pages.dev/ but then it also greys out the button and it doesn't look good for the UX that which mode is active and what can be actually clicked.
• Then I tried without the disabled flag, in which the options don't update if only that specific mode is enabled. But you can still click on the button and for a very short moment you will see the button to be off and then it turns back to white in the next frame, which worked but also was bad UX.

Hence I decided to make a flag frozen similar to disabled, which works as disabled button but with the primary color (without being greyed out).

[Keavon]

Can you go back to the approach from your second bullet point, where it briefly flashes as disabled? We can live with that for the moment. What I need to do is adapt the UI design system to better accommodate the similarities ranging from checkboxes to radio buttons so they can share certain parts of their behavior, as needed here. The little flaw can be fixed at that time.

[Keavon]

• Please ensure that, while in segment editing mode, I can still drag handles.
• In both segment and point mode, when I'm clicking down to select an anchor/handle or segment, we need the gray ghost-of-the-original-shape outline to not show up until dragging has begun, since this flashes when the mouse is down. Most visible on an open path like a "C" shape which still has a Fill node causing the straight line between endpoints to show this. (I realize this is somewhat unrelated but still worth mentioning here.)
• After Ctrl-clicking to insert a point on a selected segment, the resulting two segments should also be selected. This overrides the bullet point I'd written above:

  Upon inserting a point, it needs to not select the point, while in segment mode, since point selection shouldn't ever occur in that mode.

[Keavon]

Incomplete comment sentence

[Keavon]

I pushed my code review tweaks. I'll mark this as a draft while waiting the other requests in today's comments above. We're close on this one now!