improve gestures in perspective view

The location under your finger stays under your finger as you pan.
The location you double tap to zoom stays at the same point.
The location at the center of a pinch zoom stays at the center.
The location at the center of a rotation stays at the center.

include/mbgl/map/map.hpp

@@ -98,6 +98,7 @@ public:
 
     // Position
     void moveBy(double dx, double dy, const Duration& = Duration::zero());
+    void setLatLng(LatLng latLng, vec2<double> point, const Duration& = Duration::zero());
     void setLatLng(LatLng latLng, const Duration& = Duration::zero());
     LatLng getLatLng() const;
     void resetPosition();

platform/android/jni.cpp

@@ -637,7 +637,7 @@ void JNICALL nativeSetLatLng(JNIEnv *env, jobject obj, jlong nativeMapViewPtr, j
         return;
     }
 
-    nativeMapView->getMap().setLatLng(mbgl::LatLng(latitude, longitude), std::chrono::milliseconds(duration));
+    nativeMapView->getMap().setLatLng(mbgl::LatLng(latitude, longitude), mbgl::Duration(duration));
 }
 
 jobject JNICALL nativeGetLatLng(JNIEnv *env, jobject obj, jlong nativeMapViewPtr) {

platform/default/glfw_view.cpp

@@ -329,7 +329,10 @@ void GLFWView::onMouseMove(GLFWwindow *window, double x, double y) {
         double dx = x - view->lastX;
         double dy = y - view->lastY;
         if (dx || dy) {
-            view->map->moveBy(dx, dy);
+            double flippedY = view->height - y;
+            view->map->setLatLng(
+                    view->map->latLngForPixel(mbgl::vec2<double>(x - dx, flippedY + dy)),
+                    mbgl::vec2<double>(x, flippedY));
         }
     } else if (view->rotating) {
         view->map->rotateBy(view->lastX, view->lastY, x, y);

platform/ios/MGLMapView.mm

@@ -879,7 +879,14 @@ std::chrono::steady_clock::duration secondsAsDuration(float duration)
         CGPoint delta = CGPointMake([pan translationInView:pan.view].x - self.centerPoint.x,
                                     [pan translationInView:pan.view].y - self.centerPoint.y);
 
-        _mbglMap->moveBy(delta.x, delta.y);
+        double flippedY = self.bounds.size.height - [pan locationInView:pan.view].y;
+        _mbglMap->setLatLng(
+            _mbglMap->latLngForPixel(mbgl::vec2<double>(
+                [pan locationInView:pan.view].x - delta.x,
+                flippedY + delta.y)),
+            mbgl::vec2<double>(
+                [pan locationInView:pan.view].x,
+                flippedY));
 
         self.centerPoint = CGPointMake(self.centerPoint.x + delta.x, self.centerPoint.y + delta.y);
 
@@ -1052,7 +1059,7 @@ std::chrono::steady_clock::duration secondsAsDuration(float duration)
 
         _mbglMap->setBearing(newDegrees,
                             [rotate locationInView:rotate.view].x,
-                            [rotate locationInView:rotate.view].y);
+                            self.bounds.size.height - [rotate locationInView:rotate.view].y);
         
         [self notifyMapChange:mbgl::MapChangeRegionIsChanging];
     }

src/mbgl/map/map.cpp

@@ -166,6 +166,11 @@ void Map::setLatLng(LatLng latLng, const Duration& duration) {
     update(Update::Repaint);
 }
 
+void Map::setLatLng(LatLng latLng, vec2<double> point, const Duration& duration) {
+    transform->setLatLng(latLng, point, duration);
+    update(Update::Repaint);
+}
+
 LatLng Map::getLatLng() const {
     return transform->getLatLng();
 }

src/mbgl/map/transform.cpp

@@ -6,6 +6,7 @@
 #include <mbgl/util/math.hpp>
 #include <mbgl/util/unitbezier.hpp>
 #include <mbgl/util/interpolate.hpp>
+#include <mbgl/util/tile_coordinate.hpp>
 #include <mbgl/platform/platform.hpp>
 
 #include <cstdio>
@@ -113,6 +114,27 @@ void Transform::setLatLng(const LatLng latLng, const Duration& duration) {
     easeTo(options);
 }
 
+void Transform::setLatLng(const LatLng latLng, vec2<double> point, const Duration& duration) {
+    if (std::isnan(latLng.latitude) || std::isnan(latLng.longitude)) {
+        return;
+    }
+
+    auto coord = state.latLngToCoordinate(latLng);
+    auto coordAtPoint = state.pointToCoordinate(point);
+    auto coordCenter = state.pointToCoordinate({ state.width / 2.0f, state.height / 2.0f });
+
+    float columnDiff = coordAtPoint.column - coord.column;
+    float rowDiff = coordAtPoint.row - coord.row;
+
+    auto newLatLng = state.coordinateToLatLng({
+            coordCenter.column - columnDiff,
+            coordCenter.row - rowDiff,
+            coordCenter.zoom
+    });
+
+    setLatLng(newLatLng, duration);
+}
+
 void Transform::setLatLngZoom(const LatLng latLng, const double zoom, const Duration& duration) {
     CameraOptions options;
     options.center = latLng;
@@ -173,25 +195,20 @@ void Transform::_setScale(double new_scale, double cx, double cy, const Duration
         new_scale = state.max_scale;
     }
 
-    // Zoom in on the center if we don't have click or gesture anchor coordinates.
-    if (cx < 0 || cy < 0) {
-        cx = static_cast<double>(state.width) / 2.0;
-        cy = static_cast<double>(state.height) / 2.0;
+    const double factor = new_scale / state.scale;
+    double dx = 0;
+    double dy = 0;
+
+    if (cx > 0 || cy > 0) {
+        auto coord = state.pointToCoordinate({ cx, state.getHeight() - cy }).zoomTo(state.getZoom());
+        auto centerCoord = state.pointToCoordinate({ state.width / 2.0f, state.height / 2.0f }).zoomTo(state.getZoom());
+        auto coordDiff = centerCoord - coord;
+        dx = coordDiff.column * util::tileSize * (1.0 - factor);
+        dy = coordDiff.row * util::tileSize * (1.0 - factor);
     }
 
-    // Account for the x/y offset from the center (= where the user clicked or pinched)
-    const double factor = new_scale / state.scale;
-    const double dx = (cx - static_cast<double>(state.width) / 2.0) * (1.0 - factor);
-    const double dy = (cy - static_cast<double>(state.height) / 2.0) * (1.0 - factor);
-
-    // Account for angle
-    const double angle_sin = std::sin(-state.angle);
-    const double angle_cos = std::cos(-state.angle);
-    const double ax = angle_cos * dx - angle_sin * dy;
-    const double ay = angle_sin * dx + angle_cos * dy;
-
-    const double xn = state.x * factor + ax;
-    const double yn = state.y * factor + ay;
+    const double xn = state.x * factor - dx;
+    const double yn = state.y * factor - dy;
 
     _setScaleXY(new_scale, xn, yn, duration);
 }
@@ -318,18 +335,17 @@ void Transform::setAngle(const double new_angle, const double cx, const double c
         return;
     }
 
-    double dx = 0, dy = 0;
+    LatLng rotationCenter;
 
     if (cx >= 0 && cy >= 0) {
-        dx = (static_cast<double>(state.width) / 2.0) - cx;
-        dy = (static_cast<double>(state.height) / 2.0) - cy;
-        _moveBy(dx, dy, Duration::zero());
+        rotationCenter = state.pointToLatLng({ cx, cy });
+        setLatLng(rotationCenter, Duration::zero());
     }
 
     _setAngle(new_angle);
 
     if (cx >= 0 && cy >= 0) {
-        _moveBy(-dx, -dy, Duration::zero());
+        setLatLng(rotationCenter, { cx, cy }, Duration::zero());
     }
 }
 

src/mbgl/map/transform.hpp

@@ -29,6 +29,7 @@ public:
     // Position
     void moveBy(double dx, double dy, const Duration& = Duration::zero());
     void setLatLng(LatLng latLng, const Duration& = Duration::zero());
+    void setLatLng(LatLng latLng, vec2<double> point, const Duration& duration = Duration::zero());
     void setLatLngZoom(LatLng latLng, double zoom, const Duration& = Duration::zero());
     inline const LatLng getLatLng() const { return state.getLatLng(); }