Fm::IconInfo, scale factor and symbolic icons: not a bug but details #788
Description
Fm::IconInfo correctly scales icons with scale factors > 1; actually, it lets Qt do it. It's responsible for icons inside pcmanfm-qt's (as well as LXQt file dialog's) view and side-pane. Other icons are controlled by Qt, whether directly or through an icon engine (like that of LXQt).
But, for example, with a scale factor of 2, LXQt's icon engine will choose symbolic icons for the sizes 16×2, 22×2 and 24×2 if the icon theme supports them, while Fm::IconInfo shows ordinary icons. The end result is sharp icons in both cases but Fm::IconInfo doesn't use symbolic icons with a scale factors of 2.
You could check that by launching QT_SCALE_FACTOR=2 pcmanfm-qt (after stopping pcmanfm-qt from LXQt session settings). If your icon theme supports symbolic icons, the toolbar icons will be symbolic but the side-pane and view icons won't.
Since Fm::IconInfo takes the icon name from GIcon and uses QIconEngine to find the icon, there doesn't seem to be a place in it for dealing with scale factors directly. So, I'm not sure this could be changed in future. However, IMO, it's better to have an open issue for it.
EDIT: See #788 (comment) → 4, for why you might get confused by the Breeze icon set when testing this.