[glfw] Main loop integration

This new code can be used for rendering on the Main thread
while it will also work for rendering on the Map thread
before we make the switch. Needed by #2909.

include/mbgl/platform/default/glfw_view.hpp

@@ -2,6 +2,8 @@
 #define MBGL_COMMON_GLFW_VIEW
 
 #include <mbgl/mbgl.hpp>
+#include <mbgl/util/run_loop.hpp>
+#include <mbgl/util/timer.hpp>
 
 #ifdef MBGL_USE_GLES2
 #define GLFW_INCLUDE_ES2
@@ -92,6 +94,9 @@ private:
 
     std::function<void()> changeStyleCallback;
 
+    mbgl::util::RunLoop runLoop;
+    mbgl::util::Timer frameTick;
+
     GLFWwindow *window = nullptr;
     std::atomic_flag clean = ATOMIC_FLAG_INIT;
 };

platform/default/glfw_view.cpp

@@ -419,8 +419,16 @@ void GLFWView::onMouseMove(GLFWwindow *window, double x, double y) {
 }
 
 void GLFWView::run() {
-    while (!glfwWindowShouldClose(window)) {
-        glfwWaitEvents();
+    auto callback = [&] {
+        if (glfwWindowShouldClose(window)) {
+            frameTick.stop();
+            runLoop.stop();
+
+            return;
+        }
+
+        glfwPollEvents();
+
         const bool dirty = !clean.test_and_set();
         if (dirty) {
             const double started = glfwGetTime();
@@ -430,7 +438,10 @@ void GLFWView::run() {
                 map->update(mbgl::Update::Repaint);
             }
         }
-    }
+    };
+
+    frameTick.start(mbgl::Duration::zero(), mbgl::Milliseconds(1000 / 60), callback);
+    runLoop.run();
 }
 
 float GLFWView::getPixelRatio() const {