Rework easing transition code

This brings the easing transition code a bit closer to how easings work
in gl-js. Instead of having an array of individual transitions for scale,
rotate, and pan, there is a single transition function that does all the
required calculations. This permits us to:

* Eliminate the "timeout" transition. (Fixes #126)
* Replace start/stopPanning() et al with setGestureInProgress(). Apps or
  SDKs are expected to make paired calls to setGestureInProgress(). This
  state will be ORed with the active easing state to determine when to
  use texture interpolation. (Fixes #79)
* Run style recalculations only when an ease transition that affects the
  zoom is in progress. (Fixes #1155)

4 files changed, 16 insertions, 21 deletions

diff --git a/include/mbgl/map/map.hpp b/include/mbgl/map/map.hpp
index 436a07cb47..cdcfa27e42 100644
--- a/include/mbgl/map/map.hpp
+++ b/include/mbgl/map/map.hpp
@@ -100,13 +100,12 @@ public:
 
     // Transition
     void cancelTransitions();
+    void setGestureInProgress(bool);
 
     // Position
     void moveBy(double dx, double dy, Duration = Duration::zero());
     void setLatLng(LatLng latLng, Duration = Duration::zero());
     LatLng getLatLng() const;
-    void startPanning();
-    void stopPanning();
     void resetPosition();
 
     // Scale
@@ -117,8 +116,6 @@ public:
     double getZoom() const;
     void setLatLngZoom(LatLng latLng, double zoom, Duration = Duration::zero());
     void resetZoom();
-    void startScaling();
-    void stopScaling();
     double getMinZoom() const;
     double getMaxZoom() const;
 
@@ -128,8 +125,6 @@ public:
     void setBearing(double degrees, double cx, double cy);
     double getBearing() const;
     void resetNorth();
-    void startRotating();
-    void stopRotating();
 
     // API
     void setAccessToken(const std::string &token);
diff --git a/include/mbgl/map/transform.hpp b/include/mbgl/map/transform.hpp
index b15c119c44..ef89a4eefa 100644
--- a/include/mbgl/map/transform.hpp
+++ b/include/mbgl/map/transform.hpp
@@ -3,6 +3,7 @@
 
 #include <mbgl/map/transform_state.hpp>
 #include <mbgl/util/chrono.hpp>
+#include <mbgl/map/update.hpp>
 #include <mbgl/util/geo.hpp>
 #include <mbgl/util/noncopyable.hpp>
 #include <mbgl/util/vec.hpp>
@@ -31,8 +32,6 @@ public:
     void setLatLng(LatLng latLng, Duration = Duration::zero());
     void setLatLngZoom(LatLng latLng, double zoom, Duration = Duration::zero());
     inline const LatLng getLatLng() const { return current.getLatLng(); }
-    void startPanning();
-    void stopPanning();
 
     // Zoom
     void scaleBy(double ds, double cx = -1, double cy = -1, Duration = Duration::zero());
@@ -40,8 +39,6 @@ public:
     void setZoom(double zoom, Duration = Duration::zero());
     double getZoom() const;
     double getScale() const;
-    void startScaling();
-    void stopScaling();
     double getMinZoom() const;
     double getMaxZoom() const;
 
@@ -50,14 +47,15 @@ public:
     void setAngle(double angle, Duration = Duration::zero());
     void setAngle(double angle, double cx, double cy);
     double getAngle() const;
-    void startRotating();
-    void stopRotating();
 
     // Transitions
     bool needsTransition() const;
-    void updateTransitions(TimePoint now);
+    UpdateType updateTransitions(TimePoint now);
     void cancelTransitions();
 
+    // Gesture
+    void setGestureInProgress(bool);
+
     // Transform state
     const TransformState currentState() const;
     const TransformState finalState() const;
@@ -69,13 +67,9 @@ private:
     void _setScale(double scale, double cx, double cy, Duration = Duration::zero());
     void _setScaleXY(double new_scale, double xn, double yn, Duration = Duration::zero());
     void _setAngle(double angle, Duration = Duration::zero());
-    void _clearPanning();
-    void _clearRotating();
-    void _clearScaling();
 
     void constrain(double& scale, double& y) const;
 
-private:
     View &view;
 
     mutable std::recursive_mutex mtx;
@@ -92,10 +86,14 @@ private:
     const double min_scale = std::pow(2, 0);
     const double max_scale = std::pow(2, 18);
 
-    std::forward_list<util::ptr<util::transition>> transitions;
-    util::ptr<util::transition> scale_timeout;
-    util::ptr<util::transition> rotate_timeout;
-    util::ptr<util::transition> pan_timeout;
+    void startTransition(std::function<Update(double)> frame,
+                         std::function<void()> finish,
+                         Duration);
+
+    TimePoint transitionStart;
+    Duration transitionDuration;
+    std::function<Update(TimePoint)> transitionFrameFn;
+    std::function<void()> transitionFinishFn;
 };
 
 }
diff --git a/include/mbgl/map/transform_state.hpp b/include/mbgl/map/transform_state.hpp
index 5f2dfa49e4..c1a324a899 100644
--- a/include/mbgl/map/transform_state.hpp
+++ b/include/mbgl/map/transform_state.hpp
@@ -77,6 +77,7 @@ private:
     bool rotating = false;
     bool scaling = false;
     bool panning = false;
+    bool gestureInProgress = false;
 
     // map position
     double x = 0, y = 0;
diff --git a/include/mbgl/map/update.hpp b/include/mbgl/map/update.hpp
index 3d02434c60..3aa871bf03 100644
--- a/include/mbgl/map/update.hpp
+++ b/include/mbgl/map/update.hpp
@@ -11,6 +11,7 @@ enum class Update : UpdateType {
     Debug                     = 1 << 1,
     DefaultTransitionDuration = 1 << 2,
     Classes                   = 1 << 3,
+    Zoom                      = 1 << 4,
 };
 
 }