IIRC, the clock and calendar ones are a hack, with code in Springboard actually drawing the icons. Or at least that’s how it was at the start.
Maybe they’ve refactored it into a private API by now, though any such API would involve icon-drawing app extensions sort of like widgets, which seems a bit heavy if only a few system apps will have it as a gimmick.
Same deal on Android. OEM launcher apps override the app icons for the OEM’s calendar and clock apps, and there is no way for a different app to achieve the same effect.
IIRC, the clock and calendar ones are a hack, with code in Springboard actually drawing the icons. Or at least that’s how it was at the start.
Maybe they’ve refactored it into a private API by now, though any such API would involve icon-drawing app extensions sort of like widgets, which seems a bit heavy if only a few system apps will have it as a gimmick.
Same deal on Android. OEM launcher apps override the app icons for the OEM’s calendar and clock apps, and there is no way for a different app to achieve the same effect.