sdl: fix: concurrent drawing on Windows

On Windows, we need to prevent the event thread
from drawing at the same time as the main thread,
when window is being adjusted.

Change-Id: I2b4e4a50fec427e53e310593850e2a556a594b31

firmware/target/hosted/sdl/button-sdl.c

@@ -243,7 +243,9 @@ static bool event_handler(SDL_Event *event)
             sdl_app_has_input_focus = 0;
         else if(event->window.event == SDL_WINDOWEVENT_RESIZED)
         {
+            SDL_LockMutex(window_mutex);
             sdl_window_adjustment_needed(false);
+            SDL_UnlockMutex(window_mutex);
 #if !defined (__APPLE__) && !defined(__WIN32)
             static unsigned long last_tick;
             if (TIME_AFTER(current_tick, last_tick + HZ/20) && !button_queue_full())
@@ -354,8 +356,10 @@ static void button_event(int key, bool pressed)
     case SDLK_TAB:
         if (!pressed)
         {
+            SDL_LockMutex(window_mutex);
             background = !background;
             sdl_window_adjustment_needed(true);
+            SDL_UnlockMutex(window_mutex);
 #if !defined(__WIN32) && !defined (__APPLE__)
             button_queue_post(SDLK_UNKNOWN, 0); /* update window on main thread */
 #endif
@@ -375,12 +379,14 @@ static void button_event(int key, bool pressed)
             display_zoom = 0;
             return;
         }
+        SDL_LockMutex(window_mutex);
         if (!display_zoom)
             SDL_SetHint(SDL_HINT_RENDER_SCALE_QUALITY,
                         strcmp(SDL_GetHint(SDL_HINT_RENDER_SCALE_QUALITY) ?:
                         "best", "best") ? "best": "nearest");
 
         sdl_window_adjustment_needed(!display_zoom);
+        SDL_UnlockMutex(window_mutex);
 #if !defined(__WIN32) && !defined (__APPLE__)
         button_queue_post(SDLK_UNKNOWN, 0); /* update window on main thread */
 #endif

firmware/target/hosted/sdl/lcd-sdl.c

@@ -102,6 +102,9 @@ void sdl_gui_update(SDL_Surface *surface, int x_start, int y_start, int width,
     SDL_Rect dest= {ui_x + x_start, ui_y + y_start, width, height};
 
     uint8_t alpha;
+
+    SDL_LockMutex(window_mutex);
+
     if (SDL_GetSurfaceAlphaMod(surface,&alpha) == 0 && alpha < 255)
         SDL_FillRect(sim_lcd_surface, NULL, 0); /* alpha needs a black background */
 
@@ -111,6 +114,7 @@ void sdl_gui_update(SDL_Surface *surface, int x_start, int y_start, int width,
 
     if (!sdl_window_adjust()) /* already calls sdl_window_render itself */
         sdl_window_render();
+    SDL_UnlockMutex(window_mutex);
 }
 
 /* set a range of bitmap indices to a gradient from startcolour to endcolour */

firmware/target/hosted/sdl/system-sdl.c

@@ -175,6 +175,8 @@ void power_off(void)
 void sim_do_exit()
 {
     sim_kernel_shutdown();
+    SDL_UnlockMutex(window_mutex);
+    SDL_DestroyMutex(window_mutex);
 
     SDL_Quit();
     exit(EXIT_SUCCESS);

firmware/target/hosted/sdl/window-sdl.c

@@ -33,6 +33,8 @@ extern SDL_Surface *remote_surface;
 SDL_Texture  *gui_texture;
 SDL_Surface  *sim_lcd_surface;
 
+SDL_mutex *window_mutex;
+
 static SDL_Window   *window;
 static SDL_Renderer *sdlRenderer;
 static SDL_Surface  *picture_surface;
@@ -220,4 +222,5 @@ void sdl_window_setup(void)
 
     SDL_SetHint(SDL_HINT_RENDER_SCALE_QUALITY, display_zoom == 1 ? "best" : "nearest");
     display_zoom = 0; /* reset to 0 unless/until user requests a scale level change */
+    window_mutex = SDL_CreateMutex();
 }

firmware/target/hosted/sdl/window-sdl.h

@@ -26,6 +26,9 @@
 extern SDL_Texture *gui_texture; /* Window content, including background */
 extern SDL_Surface *sim_lcd_surface; /* LCD content */
 
+extern SDL_mutex *window_mutex;  /* prevent concurrent drawing from event thread &
+                                    main thread on MS Windows */
+
 /* Renders GUI texture. Sets up new texture, if necessary */
 void sdl_window_render(void);