PrecisionPoint TransformState::latLngToPoint dateline issue

[tobrun]

Issue in mbgl when calculating points based on LatLng from the left side of the dateline after crossing the dateline from left to right. This is a follow up issue for #3995.

An example:

Take this LatLng:

LatLng [longitude=-179.64576449708883, latitude=-16.83408606795382, altitude=0.0]

before crossing the dateline latLngToPoint is giving us Point[x=455.80133, y= 746.6456]
while after crossing the dateline latLngToPoint is giving us Point[x=393667.44, y=747.1837].
Normally we should see a small decrease in value not a big increase.

[tobrun]

Related method in transform_state.cpp:

PrecisionPoint TransformState::latLngToPoint(const LatLng& latLng) const {
    return coordinateToPoint(latLngToCoordinate(latLng));
}

which on his turn calls:

PrecisionPoint TransformState::coordinateToPoint(const TileCoordinate& coord) const {
    mat4 mat = coordinatePointMatrix(coord.zoom);
    matrix::vec4 p;
    matrix::vec4 c = {{ coord.column, coord.row, 0, 1 }};
    matrix::transformMat4(p, c, mat);
    return { p[0] / p[3], height - p[1] / p[3] };
}

and

TileCoordinate TransformState::latLngToCoordinate(const LatLng& latLng) const {
    const double tileZoom = getZoom();
    const double k = zoomScale(tileZoom) / worldSize();
    return {
        lngX(latLng.longitude) * k,
        latY(latLng.latitude) * k,
        tileZoom
    };
}

[1ec5]

I can reproduce this issue in the iOS SDK. From my location in California, if I zoom out to z0 and pan west, the user location annotation disappears as soon as the map view’s center point crosses the antimeridian. The iOS SDK similarly positions the user location annotation using Transform::latLngToPoint() (via Map::pixelForLatLng() and -[MGLMapView convertCoordinate:toPointToView:]).

[tobrun]

To make this problem a bit more visual, see this clip where I'm visualising the touch events.

[brunoabinader]

@tobrun @1ec5 this should have been fixed in fd123de - could you please test using this hash?

[tobrun]

@brunoabinader I'm on it, currently building specifically from that commit.

[tobrun]

The user location and camera are LatLng [longitude=179.931, latitude=-16.945]
At that time the user location is converted to x: 77.64928 and y: 918.33923

Just before crossing the dateline the camera is on LatLng [longitude=179.99965655644286, latitude=-16.91392665410768] the values are x: 40.649273 and y: 906.33923.

Just after crossing the dateline the camera is on LatLng [longitude=-179.99907836847547, latitude=-16.91429282823615] the values are x: 3601749.0 and y: 618666.6

While it should be almost the same as before crossing, the x value should be a bit lower.

[tobrun]

Here is the related video showing it,
note that the hash mentioned above contained this flashing regression from #4174.
which is no longer a problem on master.

[brunoabinader]

On it 👍

[brunoabinader]

👉 #4214.