[core] Move MapData storage to MapContext

This allows MapData members to hold GL resources which must be released
on the MapContext thread -- necessary for the following commit.

include/mbgl/map/map.hpp

@@ -178,8 +178,8 @@ class Map : private util::noncopyable {
 private:
     View& view;
     const std::unique_ptr<Transform> transform;
-    const std::unique_ptr<MapData> data;
     const std::unique_ptr<util::Thread<MapContext>> context;
+    MapData* data;
 
     enum class RenderState {
         never,

src/mbgl/map/map.cpp

@@ -17,8 +17,10 @@ namespace mbgl {
 Map::Map(View& view_, FileSource& fileSource, MapMode mapMode, GLContextMode contextMode, ConstrainMode constrainMode)
     : view(view_),
       transform(std::make_unique<Transform>(view, constrainMode)),
-      data(std::make_unique<MapData>(mapMode, contextMode, view.getPixelRatio())),
-      context(std::make_unique<util::Thread<MapContext>>(util::ThreadContext{"Map", util::ThreadType::Map, util::ThreadPriority::Regular}, view, fileSource, *data))
+      context(std::make_unique<util::Thread<MapContext>>(
+        util::ThreadContext{"Map", util::ThreadType::Map, util::ThreadPriority::Regular},
+        view, fileSource, mapMode, contextMode, view.getPixelRatio())),
+      data(&context->invokeSync<MapData&>(&MapContext::getData))
 {
     view.initialize(this);
     update(Update::Dimensions);

src/mbgl/map/map_context.cpp

@@ -25,9 +25,10 @@
 
 namespace mbgl {
 
-MapContext::MapContext(View& view_, FileSource& fileSource, MapData& data_)
+MapContext::MapContext(View& view_, FileSource& fileSource, MapMode mode_, GLContextMode contextMode_, const float pixelRatio_)
     : view(view_),
-      data(data_),
+      dataPtr(std::make_unique<MapData>(mode_, contextMode_, pixelRatio_)),
+      data(*dataPtr),
       asyncUpdate([this] { update(); }),
       asyncInvalidate([&view_] { view_.invalidate(); }),
       texturePool(std::make_unique<TexturePool>()) {
@@ -57,6 +58,7 @@ void MapContext::cleanup() {
     style.reset();
     painter.reset();
     texturePool.reset();
+    dataPtr.reset();
 
     glObjectStore.performCleanup();
 

src/mbgl/map/map_context.hpp

@@ -5,6 +5,7 @@
 #include <mbgl/map/update.hpp>
 #include <mbgl/map/transform_state.hpp>
 #include <mbgl/map/map.hpp>
+#include <mbgl/map/map_data.hpp>
 #include <mbgl/style/style.hpp>
 #include <mbgl/util/async_task.hpp>
 #include <mbgl/util/gl_object_store.hpp>
@@ -27,9 +28,11 @@ struct FrameData {
 
 class MapContext : public Style::Observer {
 public:
-    MapContext(View&, FileSource&, MapData&);
+    MapContext(View&, FileSource&, MapMode, GLContextMode, const float pixelRatio);
     ~MapContext();
 
+    MapData& getData() { return data; }
+
     void pause();
 
     void triggerUpdate(const TransformState&, Update = Update::Nothing);
@@ -69,6 +72,7 @@ class MapContext : public Style::Observer {
     void loadStyleJSON(const std::string& json, const std::string& base);
 
     View& view;
+    std::unique_ptr<MapData> dataPtr;
     MapData& data;
 
     util::GLObjectStore glObjectStore;

test/miscellaneous/map_context.cpp

@@ -13,9 +13,9 @@ TEST(MapContext, DoubleStyleLoad) {
     std::shared_ptr<HeadlessDisplay> display = std::make_shared<HeadlessDisplay>();
     HeadlessView view(display, 1, 512, 512);
     DefaultFileSource fileSource(nullptr);
-    MapData data(MapMode::Continuous, GLContextMode::Unique, view.getPixelRatio());
 
-    util::Thread<MapContext> context({"Map", util::ThreadType::Map, util::ThreadPriority::Regular}, view, fileSource, data);
+    util::Thread<MapContext> context({"Map", util::ThreadType::Map, util::ThreadPriority::Regular},
+        view, fileSource, MapMode::Continuous, GLContextMode::Unique, view.getPixelRatio());
 
     context.invokeSync(&MapContext::setStyleJSON, "", "");
     context.invokeSync(&MapContext::setStyleJSON, "", "");