[Gzz] The FenPDF interface

[Benja Fallenstein]

What we need
============

- Move to a buoy
- Move inside the focused article/canvas
- Select an area (for linking or transclusion)
- Make a link
- Make a transclusion

Moving inside the focused article or canvas can be done in two ways: By 
clicking where you want to go, or by dragging the article/canvas to the 
position where you want it to be. The latter 'feels' much better; to 
some degree this is be due to timing: moving to a point close to the 
focus takes a very long time when clicking there.

Actions we can use
==================

- Left click
- Left drag
- Right/middle click/drag
- Modifier key + click/drag
- Shortcut key

Everything except left click and left drag is unusual to many people.

The hardest decision
====================

It seems pretty clear that left-click should be moving to the clicked 
point. But should left drag (on the focused article/canvas) mean 
dragging the paper, or making a selection? Both are well-established 
conventions in PUIs.

Now, everything that can be done with dragging the paper can be done 
with clicking on points. Not as conveniently, yes; but if we improve the 
timing, I think it won't be horrible. Therefore, I think left drag 
should be selection, and drag-to-move-paper should be another 
button/combination.

Proposed interface
==================

First of all, I think while reading you want to be able to keep track of 
different parts of different articles. This could be done with having 
multiple cursors (foci) in different parts of the screen. But then you'd 
want to be able to store different arrangements of them and so on, and 
it would get messy.

So, I propose that at every time, you have your main focus, "what you're 
reading right now," and a PP canvas for

- bookmarks
- notes
- arranging transclusions into Memex-like trails etc

I propose that the PP canvas is a resizable region at the bottom of the 
screen, a bit like a panel but generally larger. The main (upper) focus 
can be an article or PP canvas; the secondary focus ("panel") is always 
a PP canvas. You would have the following kinds of objects on screen:

- Articles (in upper focus)
- PP canvases (in upper and lower focus)
- Buoys of an article or PP canvas
- Nodes on a PP canvas: Text, transclusion from article
- Selections on the article shown in the upper focus

Selections would be a rectangular shaded region of the article. You 
couldn't select regions on a PP canvas.

Proposed bindings
=================

- Left click on point of article or PP canvas: focus it
- Left click on PP canvas buoy: If attached to upper focus, make it the 
upper focus; if attached to lower focus, make it the lower focus
- Left click on article buoy: Make upper focus

(Yes, even if it's attached to the lower focus. Since the lower focus is 
always a PP canvas, the article buoy cannot be made the lower focus. 
Because of this, the lower focus can be used for bookmarking: simply 
transclude something there; clicking on the corresponding buoy will move 
the main focus there.)

- Left drag on focused article (outside current selection): Make 
selection (shown as translucent grey overlay). There can be at most one 
selection at a time. Moving (left clicking or dragging) destroys the 
selection; so does making a new selection, or typing on a PP canvas.

- IMPORTANT: Left drag the current selection, a buoy, or a PP node (text 
or transclusion): If dragged onto a PP canvas, transclude; if dragged 
onto another buoy/PP node/selection, make link.

While dragging, a connective line is shown from the origin of the drag 
to the position of the mouse cursor. Additionally, a translucent copy of 
the dragged area is shown under the mouse cursor, *except* if the mouse 
cursor is over a second buoy/PP node/selection. This is to show that if 
the thing is dragged here, a link will be made, not a transclusion.

So, to make a link, you select the first end and transclude it to your 
PP canvas, move to the second end, and drag it onto the first end, 
making the link.

- Right click: Show a context menu. I think context menus are very 
useful because you can never have enough mouse buttons for all the 
things that you can do to an object on the screen. The context menu will 
allow you to delete links (when clicking on a linked buoy), 
transclusions and PP text nodes (when clicking on them) and maybe PP 
canvases. On a selection/buoy/PP node, the context menu will allow you 
to transclude them onto a *new* PP canvas, so when you want to take 
notes on something on a new PP canvas, you use that. The context menu of 
a PP canvas shown in the lower focus will allow you to show it in the 
upper focus, and vice versa.

All these are very useful, but not absolutely essential for using 
FenPDF. -- The context menu will appear after you *released* the right 
mouse button, so that we can have--

- Right drag: Drag-to-move the focused article or PP canvas.

- Middle drag or left+right drag (for two button mice): Zoom / adjust 
fisheye.

- Mouse wheel or Shift-any drag (for wheelless mice): Adjust relative 
size of lower/upper focus. Wheeling up makes the lower focus bigger; 
wheeling down makes the upper focus bigger. (In other words, it's like 
you're moving the imaginary line separating the two.)

By default, the lower focus should take up approx. 1/4 of the screen, I 
think. Up for experimenting.

Opinions, please.

- Benja