Prevent the game from displaying until story screen has finished

Should fix #6867 and #3421.

src/display.cpp

@@ -2546,6 +2546,11 @@ void display::render()
 	// It is not responsible for halos and floating labels.
 	//DBG_DP << "display::render" << endl;
 
+	// No need to render if we aren't going to draw anything.
+	if(prevent_draw_) {
+		return;
+	}
+
 	// render to the offscreen buffer
 	auto target_setter = draw::set_render_target(front_);
 	draw();
@@ -2569,6 +2574,10 @@ bool display::expose(const SDL_Rect& region)
 	// Note: clipping region is set by draw_manager,
 	// and will be contained by <region>.
 
+	if(prevent_draw_) {
+		return false;
+	}
+
 	// Blit from the pre-rendered front buffer.
 	// TODO: draw_manager - API to get src region in output space
 	rect src_region = region;

src/display.hpp

@@ -563,6 +563,15 @@ public:
 	/** Checks if location @a loc or one of the adjacent tiles is visible on screen. */
 	bool tile_nearly_on_screen(const map_location &loc) const;
 
+	// TODO: draw_manager - this isn't really the correct solution
+	/** Prevent the game display from drawing.
+	  * Used while story screen is showing to prevent flicker. */
+	void set_prevent_draw(bool pd) { prevent_draw_ = pd; }
+
+private:
+	bool prevent_draw_ = false;
+
+public:
 	/** Screen fade */
 	void fade_to(const color_t& color, int duration);
 	void set_fade(const color_t& color);

src/play_controller.cpp

@@ -242,6 +242,7 @@ void play_controller::init(const config& level)
 		map_start_ = map_location(level.child_or_empty("display").child_or_empty("location"));
 		if(start_faded_) {
 			gui_->set_fade({0,0,0,255});
+			gui_->set_prevent_draw(true);
 		}
 
 		// Ensure the loading screen doesn't end up underneath the game display

src/playsingle_controller.cpp

@@ -130,6 +130,7 @@ void playsingle_controller::init_gui()
 	}
 
 	// Fade in
+	gui_->set_prevent_draw(false);
 	if(!gui_->video().any_fake()) {
 		gui_->fade_to({0,0,0,0}, 500);
 	} else {