Display corruption in panels after window shrink

[egmont]

Scenario 1:

• Go to a directory with more than a screenful of files.
• With the down arrow, place the cursor on the file that is currently visible at the bottom of the panel. (Example: if you have files named "a", "b", ... "z", and your terminal is 80x24, then you may for example see the entries from ".." (up-dir) to "n". Place the cursor over file "n" in this case.)
• Resize the window to be 1 line shorter.
• Expected behavior: the file listing should be scrolled so that the currently selected file ("n" in our example) is visible (e.g. show files from "a" to "n").
• Actual behavior: entries from ".." to "m" are shown, the cursor line disappears.

Scenario 2:

• Place the cursor on the file that's the second from the bottom (e.g. if you see entries from ".." to "n", place the cursor on "m").
• Resize the window in a single step to be 2 lines shorter. (If your window manager doesn't support this operation, then as a workaround, on top of ticket #2678's changes, you can enter the builtin viewer, resize there and then quit the viewer.)
• Expected behavior: as above
• Actual behavior: entries from "a" to "m" are shown and "m" is highlighted, so far this is okay, but then "m" is printed again where the separator line between the file list and the mini status should be.

Scenario 3, 4, etc.: Place the cursor on the 3rd (4th, etc.) visible file from the bottom, and shrink by 3 (4, etc. respectively) lines in one step. Actual behavior: as in scenario 2.

[egmont]

The function select_item() is the one that fixes the layout to make sure that the selected file is scrolled to be within the viewport. However, this function is not called on resize.

Please see the attached patch. (Of course, there are multiple possible places to place this call, you might prefer a different location.)

[egmont]

Side note: Similar bug happens when the window size is not changed, but you change an mc option that alters the panel size, e.g. you enable the hint bar. My patch happens to fix this particular case too, but I'm not sure it fixes all the cases. Probably it's not that important though :)

[egmont]

A much better version

[egmont]

I attach a much better version.

The problem was not that the infrastructure wasn't there, it was mainly some code duplication between adjust_top_file (buggy implementation) and select_item (correct implementation).

The bugs in the probably legacy adjust_top_file, which was executed at resize, are:

• off by one error: if the selected file is just below the visible area (panel->selected - old_top == llines (panel)), it does not adjust though it should.
• ugliness: modifies top_file by a lot when a small adjustment would also do, causing large unnecessary jumps of the viewport on the screen.
• ugliness: might leave some space unusused at the bottom, while files are scrolled out at the top.
• no support for "brief" file listing.

I've slightly refactored the code by moving the correct implementation to adjust_top_file. I've also refactored this good implementation a little bit and added comment to hopefully make it clearer what's going on.

Please review and apply if looks good, thanks! I hope it can make it into the next stable (4.8.1.1); after all, a display corruption on the main screen is quite ugly.

[angel_il]

branch: ​2684_always_show_selected_file
parent: master

Please review

[egmont]

Purely as a coding excercise for fun, I created an alternate version "try3". It is equally good as "try2". Pick whichever you personally prefer :)

I made some manual optimization in adjust_top_file for the code to be shorter, in the expense of probably being a tiny little bit harder to understand (but I explained it in the comment), more like in traditional "hackish" style.

The story is: in the big branch of adjust_top_file (in try2), if you reshuffle the four checks to a particular order, then there's no need for the other branch as now the big branch happens to return the desired value in that case too.

[egmont]

Alternate version, equally good as try2

[angel_il]

ARGH! :)

[egmont]

:D

(Feel free to ignore try3 :))

[andrew_b]

Merged to master.
changeset:94ffb8ba379360ec328de7fe05c69b4d3cd49825

[egmont]

Can I has backport to 4.8.1.x pretty please? :)

Soon that's going to be the stable branch for a year or even more, it'd be nice not to leave it with display corruption on the main screen.

Thanks a lot!
e.

[slavazanko]

Applied to stable:
changeset:5cebdc4bba9496e85ed3cb2e82d5b3fb5ef6e37b