Labelled polygons cause fatal crash when map rotated

[mvmcjr]

What is the bug?

If there's a polygon layer present, and you try to zoom in, the app will hang or crash on android, this happens both on a real phone and on emulator

Not sure if it happens on other platforms

How can we reproduce it?

The example app provided has the exact same problem, just open the "Polygons" page and try to zoom in:

The "zooming" level required to hang depends, but keep on zooming in until it happens

Do you have a potential solution?

No response

[JaffaKetchup]

Hi @redbaty,
Can you add the Flutter version & device information please (preferably not an emulator), and check whether running without impeller changes the result?

[mvmcjr]

Hello @JaffaKetchup

Sorry, forgot to add

This is the output of flutter doctor

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 3.29.0, on Microsoft Windows [Version 10.0.26100.3323], locale en-GB)
[✓] Windows Version (11 Pro 64-bit, 24H2, 2009)
[✓] Android toolchain - develop for Android devices (Android SDK version 35.0.0)
[✓] Chrome - develop for the web
[✓] Visual Studio - develop Windows apps (Visual Studio Community 2022 17.13.2)
[✓] Android Studio (version 2024.3)
[✓] VS Code (version 1.98.0)
[✓] Connected device (4 available)
[✓] Network resources

And I've tested on two devices:

• Motorola G7 Power running Android 9
• Samsung S24 Ultra running Android 14

Using the flag --no-enable-impeller it still hangs

[JaffaKetchup]

@redbaty Did this occur in a released version for you, or can you only reproduce on the example app?

[mvmcjr]

@JaffaKetchup Occurred both in the example app as well as in my application with version 8.1.0:

  flutter_map:
    dependency: "direct main"
    description:
      name: flutter_map
      sha256: bbf145e8220531f2f727608c431871c7457f3b134e513543913afd00fdc1cd47
      url: "https://pub.dev"
    source: hosted
    version: "8.1.0"

[mvmcjr]

Doesnt seem to happen on 8.0.0

Maybe something to do with the label?

Since the freezing seem to occur when the label would start to show

[JaffaKetchup]

What's your Polygon configuration look like? I can reproduce.

[JaffaKetchup]

The issue is indeed with labels. Likely an infinite loop of some kind? Can only reproduce on Android at the moment, but may be more due to screen size. Introduced in e9272e2, appears to occur in all 3 label positioning methods. Cause is drawLabelIfVisible within polygon painter looping infinitely.

[JaffaKetchup]

The issue occurs when the map rotation is not 0. It can occur on any platform. The issue occurs as the _buildLabelTextPainter method has not been modified to properly work across worlds.

If the rotation is 0, the first cases are always met when the text would appear off screen (and are therefore culled, stopping the layout repetitions). I'm not sure if this code is properly stable for multi-world use, but it seems to work, and I haven't had time to fully dig it out.

flutter_map/lib/src/layer/polygon_layer/label.dart

Lines 20 to 27 in 5250313

	if (rotationRad == 0) {
	if (dx + width / 2 < 0 || dx - width / 2 > mapSize.width) {
	return null;
	}
	if (dy + height / 2 < 0 || dy - height / 2 > mapSize.height) {
	return null;
	}
	}

However, if the rotation is not 0, then this statement evaluates. If true, the layout will repeat, one world over.

flutter_map/lib/src/layer/polygon_layer/label.dart

Line 31 in 5250313

if (bounds.max.dx - bounds.min.dx - padding > width) {

This statement appears to always evaluates to true if the label is within viewport at all. It does not take into consideration the shift of the world - it's only checking whether the label fits in its container (polygon bounds - padding).

The code needs to be updated to consider world shift. cc @monsieurtanuki (I'll take a look at fixing it as well.)