Inconsistencies of grip, norm and center control points in selection tool

[Antonio Ospite]

While looking into fixing the color for the newly added center control points
for shapes, I noticed a couple of things in the selection tool in the master
branch.

See the attached inkscape_selection_tool_control_points_bugs.webm file.

1. When the selection tool is active, in rotation mode, the rotation center
   control point does not show up when dragged on a black background.

2. This led me to look at the code in src/seltrans.cpp about the _norm and
   _grip control points, and I noticed that also the _norm control point
   becomes invisible on a black background, and not only in rotation mode.

   And the _grip control point is *never* displayed because of its color: it's
   basically white in XOR mode.

Can the _grip control point be removed? Or should it be made more visible?

I am going to follow up shortly with a proposal to fix these issues.

Thanks,
   Antonio

[Antonio Ospite (ospite)]

The attached file inkscape_selection_tool_control_points_fix_proposal.webm
shows my proposal to fix the issues from above.

Maybe "pause" the video when appropriate to read the text and understand what
I mean, the timing in the edit is not great. :)

Basically I propose:

1. When dragging the center control point, draw it using the color used for
   SP_KNOT_STATE_DRAGGING and the XOR blending mode.

2. Since the _norm and _grip control points are only displayed during
   dragging, show them too with the same criteria from above.

If the end result is acceptable I will clean up the local code I have and send a Merge Request.

The doubt I still have is about the _grip control point, should it be always
displayed or could it be removed completely?

FWIW I'd keep it and always display it.

Thanks,
   Antonio

[Patrick Storz (ede123)]

> The doubt I still have is about the _grip control point,
> should it be always displayed or could it be removed completely?

What do you meant with "always displayed" as far as I understand this control point will only be known once it's "gripped", so how should it always be shown?

I like all your other suggestions though, i.e.
- fixing the color of the control points to properly blend
- properly show _norm and _grip control points while dragging

[Patrick Storz (ede123)]

P.S. I don't think the _grip control point is necessary (I never missed it ;-) ), but if we already have code for it I guess it also does not hurt to fix it and show it. After all it's an indicator for the user which point is actually being dragged.

[Antonio Ospite (ospite)]

>> The doubt I still have is about the _grip control point, should it be
>> always displayed or could it be removed completely?

> What do you meant with "always displayed" as far as I understand this
> control point will only be known once it's "gripped", so how should it
> always be shown?

Yeah, I meant "displayed when DRAGGING"; the _always_ was a thinko caused by
the fact that currently the _grip control point is _never_ displayed.

Since the code is there I guess it's OK to actually show it, and if it ends up
annoying users we will have a reason to completely remove it. :)

Thanks,
   Antonio

[Antonio Ospite (ospite)]

MR sent: https://gitlab.com/inkscape/inkscape/merge_requests/55

[Antonio Ospite (ospite)]

A fix was committed in master, see the merge request page for info.

I don't think I can change the milestone field for this report.