[Bf-taskforce25] Grease Pencil - Review of UI for 2.5

[Joshua Leung]

Hi all,

While 2.5 presents many new possibilities, it is also a good time to have a
second look at some existing tools. It has come to my attention that there
are several issues that would be worthwhile to review before any porting
work commences.

1) Storage of Grease Pencil Data -> Per region? Per Area? Per Screen/Window?
Attached to data? Library Data?
In 2.4x, Grease Pencil data is stored per Area. This was based on the idea
that Grease Pencil sketches are meant to be used as temporary annotations,
that are really only valid for the context/view in which they were created
for. Following this logic, in 2.5, Grease Pencil data should be moved down
to per-region level in some cases (notably 4-split 3D-View), though this
does make context issues much more complex to define.

However, several critical issues have popped up regarding storage on
per-area instance level. The most critical of these it seems, is that there
seems to be a bit of user-interest in being able to have Grease Pencil
sketches that are able to be loaded up in difference instances of some area.
For example, when changing back and forth between two screen layouts, it may
be useful to be able to have some annotations made while viewing one of
these layouts (i.e. 3D-View in screen 1) to be available for the other (i.e.
another 3D-View in screen 2).

Another issue is the limitation of not being able to annotate screen-level
items such as headers, etc. for potential uses in making tutorials... The
other critical issue, is the lack of undo support, since data stored on
screen level is very difficult to get undo working for.

Therefore, my personal preference was (and still is) to make Grease Pencil
data library data (i.e. linkable datablocks). I should note here that this
would have happened already, had I not encountered a nasty problem where the
new datablock would just not show up in any list of datablocks, despite
having added most if not all of the necessary code in the right places.
(Perhaps it was just the choice of ID code to be 'GP', right beside the
existing 'GR' for groups?)


2) Method of Drawing
Currently in 2.4x, there are two methods of drawing with Grease Pencil:
click-drag + modifier key, or by enabling 'Draw Mode On' (in panel) and
simply click-dragging, where (shift-)LMB-click-drag draws a stroke
regardless of mouse-selection preference, and (alt-)RMB-click-drag being the
eraser.

A few notes about these methods.
- The method using modifier keys is really quite problematic with many of
our existing keymaps, and is bound to keep causing problems, since clicks
are very easily misinterpreted resulting in Grease Pencil either being
skipped or overriding the intended action.
- The more modal method ('Draw Mode On', which takes priority access to
click events) is less ideal from our non-modal/non-blocking UI paradigms.
However, in practice, this is often more practical, since when users start
sketching, they're less likely to be drawing a single isolated stroke, but
rather a series of them. Using the first method, they'd need to keep a
finger depressing some key while they should be concentrating on what to
draw instead.
Personally, I prefer the 'Draw Mode On' method.

However, with 2.5, this may prove a bit trickier to hack successfully. It
may be worthwhile to consider a third option. Headers/regions(?) would get
operator buttons which would activate the Grease Pencil modal operator. Once
this is activated, the user can draw multiple strokes as per 'Draw Mode On',
but the modal state keeps running at the end of each stroke until the user
explicitly cancels drawing with Esc. We'd need some for of indicators
(header prints?) that this was running in a semi-mode, but normal view
manipulation should still be possible (though selection may be a bit
difficult).


Anyone have any thoughts regarding the presented ideas, or any potentially
better suggestions?

Regards,
Aligorith
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