juanjo opened the ticket and wrote:

Currently dropdown lists are put above or below the widget:

1. If there is enough space below the widget that opens the list, draw it below.
2. Else, if there is enough space above the widget, draw it above.
3. Finally, if the complete list cannot be drawn because there isn't enough space, draw it below with a scrollbar.

Moreover, if 1 and 2 fails, and there is not enough space to draw at least one item below the widget, the next assert is triggered (in a not-too-close point of the code):
Assertion failed at line 688 of .../src/widgets/../widget_type.h: capacity > 0

The patch tries to change the procedure for choosing a place to draw the list:

1. If there is enough space below the widget that opens the list, draw it below.
   2b) Else, check where is more space available and see if a scrollbar is needed.
   3b) Before continuing, if there is no space for drawing a single item, stop with an assert(). (Could be changed to show an alert or debug message or to return without drawing the list).

This way, it is possible to draw a dropdown list with a scrollbar above the widget. In addition, if the list cannot be shown, an assert is triggered as well, but in a place where it is easier to understand the problem.

There are several changes on names of variables:

+int available_height = GetMainViewBottom() - top - 4;
so the expression "top + height + 4 >= GetMainViewBottom()" becomes "height >= available_height".

+int available_height_above = w->top + wi_rect.top - GetMainViewTop() - 4;
so the expression "w->top + wi_rect.top - height > GetMainViewTop()" becomes "available_height_above > height".

The expression "screen_bottom - 4 - top" becomes "available_height".

Attachments

• DropdownList.diff (3.14 KiB)

Reported version: trunk
Operating system: All

This issue was imported from FlySpray: https://bugs.openttd.org/task/6060