Map tiles showing wrongly on iOS 13 on larger screen sizes

[mvl22]

"Since latest iOS update I am getting multiple images on the map on my iPhone 8 Plus. No problem with other smaller iPhones. Reinstalling hasn’t helped."

[si-the-pie]

The image shows tiles repeating themselves across the page.
Happens on these route map styles:

• OpenCycleMap
• OpenStreetMap
• Ordnance Survey

However this style does work fine (and so is the recommended work-around):

• Apple Vector

This style doesn't work, only some of the street text and road numbers appear but the rest is blank:

• Bing Map

As experienced on iPhone 7 Plus 13.1.2

[mvl22]

[mvl22]

I can confirm this isn't a problem on iOS13 on an iPhone6S device.

So perhaps this is specific to particular larger screen sizes, i.e. later devices.

[mvl22]

Simon's phone requests tiles at 3x size as:

/opencyclemap/16/32794/21588@3x.png

from the tileserver.

[mvl22]

I suspect the problem relates to the fact that 3x tiles are being requested (which are 768x768px), but the retina tile renderer has references only to sizes 256 and 512:

https://github.com/cyclestreets/ios/blob/master/src/maps/CSRetinaTileRenderer.m

On the request side, this code I suspect is receiving 3 for %i:

https://github.com/cyclestreets/ios/blob/master/src/maps/CSOpenCycleMapSource.m#L71-L79
https://github.com/cyclestreets/ios/blob/master/src/maps/CSMapSource.m#L272-L288
https://github.com/cyclestreets/ios/blob/master/src/maps/CSRetinaTileRenderer.m#L98

Looks like MKTileOverlayPath receives the contentScaleFactor parameter from MapKit, i.e. the OS. The MapKit documentation states:

"This value is typically either 1.0 (for standard resolution displays) or 2.0 (for Retina displays)."

but perhaps there has been a change in iOS13 to supply 3.0 rather than 2.0 but this documentation not updated.

[mvl22]

The following server-side fix is now installed on the tileserver/cache config as a workaround, targetting the CycleStreets/428 release when scale is 3, downgrading it to 2, which is confirmed as fixing the issue in the app:

# Workaround bug in iOS app on iOS13; see: https://github.com/cyclestreets/ios/issues/118
if (substr_count ($_SERVER['HTTP_USER_AGENT'], 'CycleStreets/428')) {
	if (isSet ($_GET['scale']) && ($_GET['scale'] == '3')) {
		$_GET['scale'] = '2';
	}
}

However, the problem still needs to be fixed properly in the iOS codebase.

[si-the-pie]

Can we tell users that the problem is now fixed?

The immediate problem is that cached tiles will still appear and so they will think the app is still broken.

Searches suggest that the only way of clearing the app cache is to remove the app and re-install it, which is obviously a bit of a faff. Do we know how long the app keeps the tiles? The response header has Expires after 24 hours. So maybe just wait until tomoz.