Bug in updateSlidesVisibility() causes wrong display in overview mode

[steffen-mueller]

I've stumbled across the following bug in updateSlidesVisibility() and digged into it.

Reproduction

Create a presentation with 2 slide columns:

• One column with 15 slides (definitely more than the hardcoded viewDistance of 10 for the overview mode)
• One column with just one slide

Run through the presentation slide by slide. When arriving at the last slide, switch on the overview.

Instead of seeing the 15 slides in the first column, you'll only see a sad placeholder for the whole column. Moving the cursor with the arrow keys fixes the problem again.

Cause

The updateSlidesVisibility() function uses the getPreviousVerticalIndex() value as the starting point for each of the columns. As we've left the first column at say index 14, the system calculates a view distance > 10 for the first slides in the column, hiding them. The lower slides are visible but because our overflow is focussed on vertical index 0 for our first slide in column 2, we cannot see them.

Potential solution

In overflow mode, updateSlidesVisibility() should consider each column from the index of the currently selected slide (so because we had the first slide in column 2 selected, index 0) and not the previous vertical index.

Would be cool if this would be fixed soon. It's a confusing moment to have an empty overview ;) Thank you!