hide cursor on canvas, add mouse focus event, brush preview solid when small

src/app_events.cpp

@@ -7,6 +7,7 @@ void android_pick_file(android_app* mApplication, std::function<void(std::string
 #elif _WIN32
 std::string win32_open_file(const char* filter);
 std::string win32_open_dir();
+void win32_show_cursor(bool visible);
 #endif
 
 void App::crash_test()
@@ -37,6 +38,20 @@ void App::resize(float w, float h)
         main->update(w , h, zoom);
 }
 
+void App::show_cursor()
+{
+#ifdef _WIN32
+    win32_show_cursor(true);
+#endif
+}
+
+void App::hide_cursor()
+{
+#ifdef _WIN32
+    win32_show_cursor(false);
+#endif
+}
+
 void App::showKeyboard()
 {
     LOG("show keyboard");