I'm not sure this is very useful. I had an initial idea to stop using
screen_bottom1 in final_text_loc_on_screen, by starting from screen_top1
rather than screen_bottom1. But that changes the direction in which we
scan for the text line in situations where there is somehow no text on
screen (something that should never happen but I have zero confidence in
that).
Still, it doesn't seem like a bad thing to drastically reduce the
lifetime of some derived state.
Really what I need to do is throw this whole UX out and allow the cursor
to be on a drawing as a whole. So up arrow or left arrow below a drawing
would focus the whole drawing in a red border, and another up arrow and
left arrow would skip the drawing and continue upward. I think that
change to the UX will eliminate a whole class of special cases in the
code.
Thanks Alex Schroeder for reporting this crash. The scenario:
* Edit a file like say this repo's Readme.
* The second line is empty and there's a '+' to insert a drawing.
Click on that.
* Resize the window so just the first line of text and the drawing are
visible.
* Close the window.
* Reopen lines.love, it will reopen the same file.
* Click on the left margin to the left of the drawing.
Before this commit these steps yielded the following crash:
Error: bad argument #1 to 'len' (string expected, got nil)
text.lua:626: in function 'pos_at_end_of_screen_line'
edit.lua:298: in function 'mouse_press'
There were two distinct problems here:
1. State.screen_bottom1 is not required to point to a text line, it
could just as well be a drawing. I have been sloppy in handling that.
2. The bug was partially masked (the need to close and reopen the
window) by a second bug: inserting a drawing was not invalidating the
cache I save of starty coordinates for each line. (I've inserted and
deleted starty invalidations a few times in the past, but it looks
like I'd never had one in this particular location edit.draw before.)
How did these issues get missed for years?
- Even though I use lines.love on a daily basis, it turns out I don't
actually create line drawings all that often.
- When I do, I'm still living in files that are mostly text with only
an occasional drawing.
- I keep my windows fairly large.
Between these 3 patterns, the odds of running into a drawing as the
first or bottom-most line on the screen were fairly small. And then I
had to interact with it. I suspect I tend to interact with drawings
after centering them vertically.
---
Bug #1 in particular has some interesting past history.
* Near the start of the project, when I implemented line-wrapping I
started saving screen_bottom, the bottom-most line displayed on
screen. I did this so I could scroll down easily just by assigning
`screen_top = screen_bottom`. (On the other hand, scrolling up still
required some work. I should perhaps get rid of it and just compute
scrolls from scratch each time.)
* Also near the start of the project, I supported selecting text by a
complex state machine spanning keypress, mouse press and mouse
release:
mouse click (press and immediate release) moves cursor
mouse drag (press and much later release) creates selection
shift-click selects from current cursor to click location
shift-movement creates/grows a selection
* On 2023-06-01, inscript reported a bug. Opening a window with just a
little bit of text (lots of unused space in the window), selecting all
the text and then clicking below all the text would crash the editor.
To fix this I added code at the bottom of edit.mouse_press which
computed the final visible line+pos location and used that in the
cursor-move/text-selection state machine. It did this computation
based on.. screen_bottom. But I didn't notice that screen_bottom could
be a drawing (which has no pos). This commit's bug/regression was
created.
* On 2023-09-20, Matt Wynne encountered a crash which got me to realize
I need code at the bottom of edit.mouse_release symmetric to the code
at the bottom of edit.mouse_press. I still didn't notice that
screen_bottom could be a drawing.
So in fixing inscript's bug report, I introduced (at least) 2
regressions, because I either had no idea or quickly forgot that
screen_bottom could point at a drawing.
While I created regressions, the underlying mental bug feels new. I just
never focused on the fact that screen_bottom could point at a drawing.
This past history makes me suspicious of my mouse_press/mouse_release
code. I think I'm going to get rid of screen_bottom entirely as a
concept. I'll still have to be careful though about the remaining
locations and which of them are allowed to point at drawings:
- cursor and selection are not allowed to point at drawings
- screen_top and screen_bottom are allowed to point at drawings
I sometimes copy between these 4 location variables. Auditing shows no
gaps where cursor could ever end up pointing at a drawing. It's just
when I started using screen_bottom for a whole new purpose (in
the mouse_press/release state machine) that I went wrong.
I should also try getting rid of starty entirely. Is it _really_ needed
for a responsive editor? I think I introduced it back when I didn't know
what I was doing with LÖVE and was profligately creating text objects
willy-nilly just to compute widths.
Getting rid of these two fairly global bits of mutable state will
hopefully make lines much more robust when the next person tries it out
in 6 months :-/ X-(
Thanks everyone for the conversation around this bug:
https://merveilles.town/@akkartik/112567862542495637
---
Bug #2 has some complexity as well, and might lead to some follow-on
cleanup.
When I click on the button to insert a new drawing, the mouse_release
hook triggers and moves the cursor below the new drawing. This is
desirable, but I'd never noticed this happy accident. It stops working
when I invalidate starty for all lines (which gets recomputed and cached
for all visible lines on every frame).
Fixing this caused a couple of unit tests start crashing for 2 reasons
that required their own minor fixes:
- My emulated mouse press and release didn't have an intervening
frame and so mouse_release no longer receives starty. Now I've added
a call to edit.draw() between press and release.
This might actually bite someone for real someday, if they're
running on a slow computer or something like that. I've tried to
click really fast but I can't seem to put mouse_press and release in
the same frame (assuming 30 frames per second)
- My tests' window dimensions often violate my constraint that the
screen always have one line of text for showing the cursor. They're
unrealistically small or have a really wide aspect ratio (width 2x
of height). I suspect lines.love will itself crash in those
situations, but hopefully they're unrealistic. Hmm, I wonder what
would happen if someone maximized in a 16:9 screen, that's almost
2x.. Anyways, I've cleaned a couple of tests up, but might need to
fix up others at some point. I'd have to rejigger all my brittle
line-wrapping tests if I modify the screen width :-/ X-(
scenario:
- create a long wrapping line
- tap past end of first screen line
Before this commit the cursor would be positioned not quite at the end
of the screen line but one character before. In effect there was no way
to position cursor at end of a wrapping line.
I'm not sure how this bug has lasted so long. It was introduced in
commit 8d3adfa36 back in June 2022, which was itself billed as a bugfix
for "clicking past end of screen line". But when I go back to it this
bug exists even back then. How did I miss it?! I wrote a test back then
-- and the test was wrong, has always been wrong.
I'm not sure this can trigger everywhere (I've only been able to
exercise it in Lua Carousel), but it seems like a safety net worth
having against future modifications by anybody.
This commit doesn't guarantee we'll always catch it. But if this
invariant is violated, things can get quite difficult to debug. I found
in the Lua Carousel fork that all the xpcalls I keep around were
actively hindering my ability to notice this invariant being violated.
Each one should provide a message that will show up within LÖVE. Stop
relying on nearby prints to the terminal.
I also found some unnecessary ones.
There is some potential here for performance regressions: the format()
calls will trigger whether or not the assertion fails, and cause
allocations. So far Lua's GC seems good enough to manage the load even
with Moby Dick, even in some situations that caused issues in the past
like undo.
scenario:
* position a wrapped line on screen
* search for the word immediately after the point of wrapping
Before this commit the word would be highlighted twice:
- at the end of the first screen line
- at the start of the second screen line
Now it shows up at the right place.
To fix this I have to first stop incrementally updating screen_bottom1
in the middle of a frame. Now it always has a good value from the end of
a frame.
I'm also running into some limitations in the test I'd ideally like to
write (that are documented in a comment), but I still get some sort of
automated test for this bugfix.
This is a violation of an existing rule in Manual_tests.md. The
following command weakly suggests there aren't any others:
grep ':sub(' *.lua |grep pos
A code editor is unlikely to need support for extremely long lines. And
that kind of scroll is jarring anyway in a code editor. We don't read
code like a novel, and less scroll per page implies more scrolling work.
I'd gotten rid of this functionality and the test for it [1] back in the
spokecone fork, but only took out the test when first pulling it into
the source editor.
[1] test_pagedown_often_shows_start_of_wrapping_line
This doesn't affect this fork directly, but it's a bad idea to assume
the _app_ is always going to be doing just what a particular subsystem
(here, the text editor in edit.lua+text.lua) is doing.
I think all we need to maintain is the populate_screen_line_starting_pos
array. It's easy to render screen lines one by one from it, and we'll
only ever construct one additional screen line at a time.
I'd hoped to delete other calls to Text.populate_screen_line_starting_pos,
but it turns out we need to update it when editing sometimes. Give up on
that for now; it's a no-op if not needed.
It's just uneconomic to maintain given how little I've used it. I have a
bug right now and no time to port the bugfix to all the complexities of
the B side.
I briefly considered tossing out the entire source editor. But I _have_
been using it to browse logs across sessions. The live editor doesn't
quite cover all my use cases just yet.
We now have duplication in the source editor only for:
* syntax highlighting
* hyperlinking [[WikiWords]]
* ability to hide cursor (when showing file browser or Focus is in log browser)