drive map rendering from main thread

android/cpp/native_map_view.cpp

@@ -124,12 +124,16 @@ void NativeMapView::deactivate() {
     }
 }
 
-void NativeMapView::invalidate(std::function<void()> render) {
+void NativeMapView::invalidate() {
+    mbgl::Log::Debug(mbgl::Event::Android, "NativeMapView::invalidate");
+
+    // TODO: inform the main thread that it must call map->renderSync();
+}
+
+void NativeMapView::swap() {
     mbgl::Log::Debug(mbgl::Event::Android, "NativeMapView::invalidate");
 
     if ((display != EGL_NO_DISPLAY) && (surface != EGL_NO_SURFACE)) {
-        render();
-
         if (!eglSwapBuffers(display, surface)) {
             mbgl::Log::Error(mbgl::Event::OpenGL, "eglSwapBuffers() returned error %d",
                              eglGetError());

include/mbgl/android/native_map_view.hpp

@@ -23,7 +23,8 @@ public:
     void activate() override;
     void deactivate() override;
     void notify() override;
-    void invalidate(std::function<void()> render) override;
+    void invalidate() override;
+    void swap() override;
 
     void notifyMapChange(mbgl::MapChange change, Duration delay = Duration::zero()) override;
 

include/mbgl/map/view.hpp

@@ -44,9 +44,11 @@ public:
     virtual void resize(uint16_t width, uint16_t height, float pixelRatio);
 
     // Called from the render thread. The implementation must trigger a rerender.
-    // (i.e. either the passed render() function for rendering immediately on the map thread,
-    // or map->renderSync() from the main thread must be called as a result of this)
-    virtual void invalidate(std::function<void()> render) = 0;
+    // (map->renderSync() from the main thread must be called as a result of this)
+    virtual void invalidate() = 0;
+
+    // Called from the render thread after the render is complete.
+    virtual void swap() = 0;
 
     // Reads the pixel data from the current framebuffer. If your View implementation
     // doesn't support reading from the framebuffer, return a null pointer.

include/mbgl/platform/default/glfw_view.hpp

@@ -8,6 +8,8 @@
 #endif
 #include <GLFW/glfw3.h>
 
+#include <atomic>
+
 class GLFWView : public mbgl::View {
 public:
     GLFWView(bool fullscreen = false);
@@ -17,7 +19,8 @@ public:
     void activate() override;
     void deactivate() override;
     void notify() override;
-    void invalidate(std::function<void()> render) override;
+    void invalidate() override;
+    void swap() override;
 
     static void onKey(GLFWwindow *window, int key, int scancode, int action, int mods);
     static void onScroll(GLFWwindow *window, double xoffset, double yoffset);
@@ -62,6 +65,7 @@ private:
     std::function<void()> changeStyleCallback;
 
     GLFWwindow *window = nullptr;
+    std::atomic_flag clean = ATOMIC_FLAG_INIT;
 };
 
 #endif

include/mbgl/platform/default/headless_view.hpp

@@ -33,7 +33,8 @@ public:
     void deactivate() override;
     void notify() override;
     void resize(uint16_t width, uint16_t height, float pixelRatio) override;
-    void invalidate(std::function<void()> render) override;
+    void invalidate() override;
+    void swap() override;
     std::unique_ptr<StillImage> readStillImage() override;
 
 private:

platform/default/glfw_view.cpp

@@ -282,6 +282,10 @@ void GLFWView::onMouseMove(GLFWwindow *window, double x, double y) {
 void GLFWView::run() {
     while (!glfwWindowShouldClose(window)) {
         glfwWaitEvents();
+        const bool dirty = !clean.test_and_set();
+        if (dirty) {
+            map->renderSync();
+        }
     }
 }
 
@@ -297,8 +301,12 @@ void GLFWView::notify() {
     glfwPostEmptyEvent();
 }
 
-void GLFWView::invalidate(std::function<void()> render) {
-    render();
+void GLFWView::invalidate() {
+    clean.clear();
+    glfwPostEmptyEvent();
+}
+
+void GLFWView::swap() {
     glfwSwapBuffers(window);
     fps();
 }

platform/default/headless_view.cpp

@@ -280,8 +280,12 @@ void HeadlessView::deactivate() {
 #endif
 }
 
-void HeadlessView::invalidate(std::function<void()> render) {
-    render();
+void HeadlessView::invalidate() {
+    // no-op
+}
+
+void HeadlessView::swap() {
+    // no-op
 }
 
 }

platform/ios/MGLMapView.mm

@@ -2755,13 +2755,18 @@ class MBGLView : public mbgl::View
         [EAGLContext setCurrentContext:nil];
     }
 
-    void invalidate(std::function<void()>) override
+    void invalidate() override
     {
         [nativeView performSelectorOnMainThread:@selector(invalidate)
                                      withObject:nil
                                   waitUntilDone:NO];
     }
 
+    void swap() override
+    {
+        // no-op
+    }
+
     private:
         __weak MGLMapView *nativeView = nullptr;
 };

src/mbgl/map/map.cpp

@@ -43,7 +43,7 @@ void Map::renderStill(StillImageCallback callback) {
 }
 
 void Map::renderSync() {
-    context->invokeSync(&MapContext::render);
+    context->invokeSync(&MapContext::renderSync);
 }
 
 void Map::update(Update update_) {

src/mbgl/map/map_context.cpp

@@ -269,7 +269,11 @@ void MapContext::update() {
             }
         }
 
-        view.invalidate([this] { render(); });
+        if (mayRender) {
+            render();
+        } else {
+            view.invalidate();
+        }
     }
 
     updated = static_cast<UpdateType>(Update::Nothing);
@@ -302,9 +306,16 @@ void MapContext::renderStill(StillImageCallback fn) {
     }
 
     callback = fn;
+    mayRender = true;
     triggerUpdate(Update::RenderStill);
 }
 
+void MapContext::renderSync() {
+    mayRender = true;
+    render();
+    mayRender = false;
+}
+
 void MapContext::render() {
     assert(util::ThreadContext::currentlyOn(util::ThreadType::Map));
 
@@ -326,11 +337,15 @@ void MapContext::render() {
     painter->setDebug(data.getDebug());
     painter->render(*style, transformState, data.getAnimationTime());
 
+    mayRender = false;
+
     if (data.mode == MapMode::Still) {
         callback(nullptr, view.readStillImage());
         callback = nullptr;
     }
 
+    view.swap();
+
     // Schedule another rerender when we definitely need a next frame.
     if (data.transform.needsTransition() || style->hasTransitions()) {
         triggerUpdate();
@@ -351,7 +366,7 @@ void MapContext::setSourceTileCacheSize(size_t size) {
         for (const auto &source : style->sources) {
             source->setCacheSize(sourceCacheSize);
         }
-        view.invalidate([this] { render(); });
+        view.invalidate();
     }
 }
 
@@ -361,7 +376,7 @@ void MapContext::onLowMemory() {
     for (const auto &source : style->sources) {
         source->onLowMemory();
     }
-    view.invalidate([this] { render(); });
+    view.invalidate();
 }
 
 void MapContext::onTileDataChanged() {

src/mbgl/map/map_context.hpp

@@ -34,12 +34,12 @@ public:
     ~MapContext();
 
     void pause();
-    void render();
 
     void resize(uint16_t width, uint16_t height, float ratio);
 
     using StillImageCallback = std::function<void(std::exception_ptr, std::unique_ptr<const StillImage>)>;
     void renderStill(StillImageCallback callback);
+    void renderSync();
 
     void triggerUpdate(Update = Update::Nothing);
 
@@ -62,6 +62,7 @@ public:
 
 private:
     void updateTiles();
+    void render();
 
     // Style-related updates.
     void cascadeClasses();
@@ -88,6 +89,7 @@ private:
     std::string styleURL;
     std::string styleJSON;
 
+    bool mayRender = false;
     StillImageCallback callback;
     size_t sourceCacheSize;
     TransformState transformState;

test/fixtures/mock_view.hpp

@@ -1,5 +1,5 @@
-#ifndef TEST_RESOURCES_MOCK_VIEW
-#define TEST_RESOURCES_MOCK_VIEW
+#ifndef TEST_FIXTURES_MOCK_VIEW
+#define TEST_FIXTURES_MOCK_VIEW
 
 #include <mbgl/map/view.hpp>
 
@@ -13,7 +13,8 @@ public:
     void activate() override {};
     void deactivate() override {};
     void notify() override {};
-    void invalidate(std::function<void()>) override {};
+    void invalidate() override {}
+    void swap() override {}
 };
 
 }

test/miscellaneous/transform.cpp

@@ -1,4 +1,5 @@
 #include "../fixtures/util.hpp"
+#include "../fixtures/mock_view.hpp"
 
 #include <mbgl/util/run_loop.hpp>
 #include <mbgl/map/map_data.hpp>
@@ -11,18 +12,6 @@
 
 using namespace mbgl;
 
-class MockView : public View {
-public:
-    void activate() override {
-    }
-    void deactivate() override {
-    }
-    void notify() override {
-    }
-    void invalidate(std::function<void()>) override {
-    }
-};
-
 TEST(Transform, InvalidScale) {
     MockView view;
     Transform transform(view);

test/style/resource_loading.cpp

@@ -1,7 +1,7 @@
 #include "../fixtures/fixture_log_observer.hpp"
 #include "../fixtures/util.hpp"
+#include "../fixtures/mock_view.hpp"
 #include "mock_file_source.hpp"
-#include "mock_view.hpp"
 
 #include <mbgl/map/map_data.hpp>
 #include <mbgl/map/transform_state.hpp>