[core] Do not constrain on X axis in ConstrainMode::HeightOnly

1 files changed, 15 insertions, 10 deletions

diff --git a/src/mbgl/map/transform_state.cpp b/src/mbgl/map/transform_state.cpp
index 9ff68a1a60..5cbd307698 100644
--- a/src/mbgl/map/transform_state.cpp
+++ b/src/mbgl/map/transform_state.cpp
@@ -352,21 +352,26 @@ bool TransformState::rotatedNorth() const {
 }
 
 void TransformState::constrain(double& scale_, double& x_, double& y_) const {
-    // Constrain minimum scale to avoid zooming out far enough to show off-world areas.
-    scale_ = util::max(scale_,
-                       static_cast<double>(rotatedNorth() ? size.height : size.width) / util::tileSize,
-                       static_cast<double>(rotatedNorth() ? size.width : size.height) / util::tileSize);
+    if (constrainMode == ConstrainMode::None) {
+        return;
+    }
+
+    const double ratioX = (rotatedNorth() ? size.height : size.width) / util::tileSize;
+    const double ratioY = (rotatedNorth() ? size.width : size.height) / util::tileSize;
+
+    // Constrain minimum scale to avoid zooming out far enough to show off-world areas on the Y axis.
+    // If Y axis ratio is too small to be constrained, use X axis ratio instead.
+    scale_ = util::max(scale_, ratioY < 1.0 ? ratioX : ratioY);
+
+    // Constrain min/max pan to avoid showing off-world areas on the Y axis.
+    double max_y = (scale_ * util::tileSize - (rotatedNorth() ? size.width : size.height)) / 2;
+    y_ = std::max(-max_y, std::min(y_, max_y));
 
-    // Constrain min/max pan to avoid showing off-world areas.
     if (constrainMode == ConstrainMode::WidthAndHeight) {
+        // Constrain min/max pan to avoid showing off-world areas on the X axis.
         double max_x = (scale_ * util::tileSize - (rotatedNorth() ? size.height : size.width)) / 2;
         x_ = std::max(-max_x, std::min(x_, max_x));
     }
-
-    if (constrainMode != ConstrainMode::None) {
-        double max_y = (scale_ * util::tileSize - (rotatedNorth() ? size.width : size.height)) / 2;
-        y_ = std::max(-max_y, std::min(y_, max_y));
-    }
 }
 
 void TransformState::moveLatLng(const LatLng& latLng, const ScreenCoordinate& anchor) {