Round tap-zoom gestures to nearest integer

[friedbunny]

iOS changes

Rounds double-tap and two-finger tap zoom gestures to the nearest integer zoom level. This has benefits for raster tiles, as well as styles with zoom-based functions that transition on integers.

This results in a wider possible zoom range per gesticulation — 1.0 → ~0.5-1.5 levels. Here’s a comparison of double-tapping to zoom in with the changes in this PR:

Starting Zoom	Old Result	New Result
4.0	5.0 (+1.0)	5.0 (+1.0)
4.4	5.4 (+1.0)	5.0 (+0.6)
4.6	5.6 (+1.0)	6.0 (+1.4)

Fixes #2276.

Core changes

Exposes an already-existing setZoom variation that takes an anchor parameter — I did this to avoid calculating scale levels in the iOS zoom code. This makes Map::setZoom(zoom, {}, duration) ambiguous, so it’s now necessary to specify a type for the middle parameter.

[mention-bot]

@friedbunny, thanks for your PR! By analyzing this pull request, we identified @incanus, @1ec5 and @jfirebaugh to be potential reviewers.

[1ec5]

Can you make the corresponding changes to the Zoom In and Zoom Out buttons in the Android and macOS SDKs?

mapbox-gl-native/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/Transform.java

Lines 180 to 184 in e6c15d0

	if (zoomIn) {
	mapView.scaleBy(2.0, x, y, MapboxConstants.ANIMATION_DURATION);
	} else {
	mapView.scaleBy(0.5, x, y, MapboxConstants.ANIMATION_DURATION);
	}

mapbox-gl-native/platform/macos/src/MGLMapView.mm

Line 1045 in e6c15d0

[self setZoomLevel:self.zoomLevel + zoomDelta animated:animated];

/cc @tobrun

[friedbunny]

Went a bit further on macOS in 4ed80f9 and rounded all of the non-freeform zoom methods gestures and commands.

[friedbunny]

I’ll leave Android to @tobrun, in light of #7630.

[friedbunny]

As an extreme example, here’s Mapbox Streets at z10.99 vs z11.00:

[1ec5]

Looks good, and thanks also for the changes on the macOS side. I’ll leave it to you to decide whether the Android SDK should get this fix here or in a separate PR.

[1ec5]

FYI, the ⌥↑ and ⌥↓ shortcuts are built into MGLMapView. The menu items (which have their own shortcuts) are defined in MapDocument but could conceivably be moved into MGLMapView as well.

[friedbunny]

Ah, did not know that — I’ll update the text here.

[1ec5]

It looks like #7630 would’ve implemented a similar fix on the Android side. Not sure why @tobrun closed it.

[tobrun]

@1ec5 @friedbunny I initially created that PR to showcase the possibility of such a feature but this didn't make it to master at that time as I didn't want to change the "default" behaviour. We could definitely look into reopening it for consistency between the bindings.

cc @mapbox/android

[zugaldia]

We could definitely look into reopening it for consistency between the bindings.

Yeah, let's do that for 5.0. It doesn't look like a big lift.

[1ec5]

The Android side is happening once again in #7630. 🚢