Panel Scroll Center

[Miven]

This patch adds an option, Center &scrolling, to the panel options dialog.

Behavior: This patch causes the panel to begin scrolling when the cursor reaches the middle of the panel, so that the cursor *tends* to stay in the middle of the panel on long listings. Only when you reach the beginning or the end of the listing will the cursor move to the first or last file.

Included is a patch for 5 files:
doc/man/mc.1.in
src/setup.h
src/setup.c
src/filemanager/boxes.c
src/filemanager/panel.c

These were diffed from the latest git repo of 4.8.11.

[Miven]

panel-scroll-center diff

[gotar]

This would be a great feature - I've thought about this many times (and forgot to create feature request), but extended to allow setting some boundaries (range) that selection could move inside before scrolling.

[andrew_b]

Branch: 3130_panel_center_scroll.
Initial changeset:f6306f2c98b5a3de04d3d6b1569c3e1cc1d78ad7

[zaytsev]

I'm a bit bothered by the copy-paste under /* define top file of column */ :-/ Too bad C doesn't have lambdas. Do you think it's worth it extracting into a small function?

[andrew_b]

Replying to zaytsev:

Do you think it's worth it extracting into a small function?

Lets's consider two cases.

1.

static int
panel_get_top_file_at_column (const WPanel * panel)
{
    int lines, top;

    lines = panel_lines (panel);

    top = panel->top_file;
    if (panel->list_cols > 1)
        top += lines * ((panel->selected - top) / lines);

    return top;
}

In this case lines is required twice: inside and outsize panel_get_top_file_at_column(). Thus, lines is calculated twice.

2.

static int
panel_get_top_file_at_column (const WPanel * panel, int lines)
{
    int top;

    top = panel->top_file;
    if (panel->list_cols > 1)
        top += lines * ((panel->selected - top) / lines);

    return top;
}

In this case lines is calculated once and passed into panel_get_top_file_at_column(). This looks like lines and panel are not matched but is not true.

Both cases are bad in my view.

[zaytsev]

So, how about the following code:

static int
i_cant_think_of_a_good_name_because_im_tired (const WPanel * panel)
{
    int lines, top;

    lines = panel_lines (panel);

    top = panel->top_file;
    if (panel->list_cols > 1)
        top += lines * ((panel->selected - top) / lines);

    return (panel->selected - top) - (lines / 2);
}

...


/* Scroll window when cursor is halfway down */ 
if ( i_cant_think_of_a_good_name_because_im_tired(panel) > 0) 
{ 
    panel->top_file++; 
    if (panel->top_file > panel->dir.len - items) 
        panel->top_file = panel->dir.len - items; 
}

...

/* Scroll window when cursor is halfway up */ 
if ( i_cant_think_of_a_good_name_because_im_tired(panel) < 0) 
{ 
    panel->top_file--; 
    if (panel->top_file < 0) 
        panel->top_file = 0; 
}

I must be certainly missing something (apart from a good name for the function, my brain is completely burned out now)...

[andrew_b]

Replying to zaytsev:

So, how about the following code:

Great! I added the fixup changeset:df62684006ec11e18e937bc19d33e781de7d1715
The better name of function is welcome!

[zaytsev]

The better name of function is welcome!

I would say maybe "panel_selected_relative_to_middle", but that's quite long. Everything looks good!

[andrew_b]

Merged to master: [4b142c7637af7ef206cb1b02655cdbb352aab3b6].

git log --pretty=oneline 82fc95f..4b142c7