Fix the --screenshot commandline arg.

A new fake video mode video::fake::hide_window was added,
as screenshots need a rendering context and thus a window.
It draws everything as normal, just with the window hidden.

The other fake modes were also renamed to increase clarity a bit.

src/display.cpp

@@ -790,7 +790,10 @@ surface display::screenshot(bool map_screenshot)
 
 	map_screenshot_ = true;
 
+	DBG_DP << "invalidating region for map screenshot";
 	invalidate_locations_in_rect(map_area());
+
+	DBG_DP << "drawing map screenshot";
 	draw();
 
 	map_screenshot_ = false;
@@ -800,6 +803,7 @@ surface display::screenshot(bool map_screenshot)
 	ypos_ = old_ypos;
 
 	// Read rendered pixels back as an SDL surface.
+	LOG_DP << "reading pixels for map screenshot";
 	return video::read_pixels();
 }
 
@@ -1301,6 +1305,9 @@ void display::drawing_buffer_add(const drawing_layer layer, const map_location&
 
 void display::drawing_buffer_commit()
 {
+	DBG_DP << "committing drawing buffer"
+	       << " with " << drawing_buffer_.size() << " items";
+
 	// std::list::sort() is a stable sort
 	drawing_buffer_.sort();
 
@@ -2394,7 +2401,7 @@ void display::draw()
 	set_scontext_unsynced leave_synced_context;
 
 	// This isn't the best, but also isn't important enough to do better.
-	if(redraw_background_) {
+	if(redraw_background_ && !map_screenshot_) {
 		DBG_DP << "display::draw redraw background";
 		render_map_outside_area();
 		draw_manager::invalidate_region(map_outside_area());
@@ -3133,7 +3140,7 @@ void display::invalidate_all()
 
 bool display::invalidate(const map_location& loc)
 {
-	if(invalidateAll_)
+	if(invalidateAll_ && !map_screenshot_)
 		return false;
 
 	bool tmp;
@@ -3143,7 +3150,7 @@ bool display::invalidate(const map_location& loc)
 
 bool display::invalidate(const std::set<map_location>& locs)
 {
-	if(invalidateAll_)
+	if(invalidateAll_ && !map_screenshot_)
 		return false;
 	bool ret = false;
 	for (const map_location& loc : locs) {
@@ -3186,7 +3193,7 @@ bool display::invalidate_visible_locations_in_rect(const SDL_Rect& rect)
 
 bool display::invalidate_locations_in_rect(const SDL_Rect& rect)
 {
-	if(invalidateAll_)
+	if(invalidateAll_ && !map_screenshot_)
 		return false;
 
 	DBG_DP << "invalidating locations in " << rect;

src/game_launcher.cpp

@@ -313,6 +313,7 @@ bool game_launcher::init_video()
 {
 	// Handle special commandline launch flags
 	if(cmdline_opts_.nogui
+		|| cmdline_opts_.screenshot
 		|| cmdline_opts_.headless_unit_test
 		|| cmdline_opts_.render_image)
 	{
@@ -325,7 +326,14 @@ bool game_launcher::init_video()
 			PLAIN_LOG << "--nogui flag is only valid with --multiplayer or --screenshot or --plugin flags";
 			return false;
 		}
-		video::init(video::fake::window);
+		if(cmdline_opts_.screenshot) {
+			// Screenshots require a rendering context, and thus a window,
+			// so we create one but hidden.
+			video::init(video::fake::hide_window);
+		} else {
+			// Other functions don't require a window at all.
+			video::init(video::fake::no_window);
+		}
 		game_config::no_delay = true;
 		return true;
 	}

src/tests/utils/fake_display.cpp

@@ -68,7 +68,7 @@ fake_display_manager::fake_display_manager()
 	, main_event_context_()
 	, disp_(dummy_board_, std::shared_ptr<wb::manager>(), dummy_reports, "", dummy_cfg_)
 {
-	video::init(video::fake::draw);
+	video::init(video::fake::no_draw);
 }
 
 game_display& fake_display_manager::get_display()

src/video.cpp

@@ -74,7 +74,7 @@ namespace video
 void render_screen(); // exposed and used only in draw_manager.cpp
 
 // Internal functions
-static void init_window();
+static void init_window(bool hidden=false);
 static void init_test_window();
 static void init_fake();
 static void init_test();
@@ -98,12 +98,15 @@ void init(fake type)
 	case fake::none:
 		init_window();
 		break;
-	case fake::window:
+	case fake::no_window:
 		init_fake();
 		break;
-	case fake::draw:
+	case fake::no_draw:
 		init_test();
 		break;
+	case fake::hide_window:
+		init_window(true);
+		break;
 	default:
 		throw error("unrecognized fake type passed to video::init");
 	}
@@ -151,6 +154,7 @@ bool testing()
 
 void init_fake()
 {
+	LOG_DP << "running headless";
 	headless_ = true;
 	refresh_rate_ = 1;
 	game_canvas_size_ = {800,600};
@@ -351,7 +355,7 @@ void init_test_window()
 	update_test_framebuffer();
 }
 
-void init_window()
+void init_window(bool hidden)
 {
 	// Position
 	const int x = preferences::fullscreen() ? SDL_WINDOWPOS_UNDEFINED : SDL_WINDOWPOS_CENTERED;
@@ -374,6 +378,11 @@ void init_window()
 		window_flags |= SDL_WINDOW_MAXIMIZED;
 	}
 
+	if(hidden) {
+		LOG_DP << "hiding main window";
+		window_flags |= SDL_WINDOW_HIDDEN;
+	}
+
 	uint32_t renderer_flags = SDL_RENDERER_ACCELERATED | SDL_RENDERER_TARGETTEXTURE;
 
 	if(preferences::vsync()) {

src/video.hpp

@@ -38,10 +38,11 @@ namespace video
 /**
  * For describing the type of faked display, if any.
  *
- * fake::window never tries to create a window, or draw anything.
- * fake::draw does create an offscreen window, but does not draw to it.
+ * fake::no_window never tries to create a window, or draw anything.
+ * fake::no_draw does create an offscreen window, but does not draw to it.
+ * fake::hide_window creates a window as normal, but does not display it.
  */
-enum class fake { none, window, draw };
+enum class fake { none, no_window, no_draw, hide_window };
 
 /**
  * Initialize the video subsystem.

src/wesnoth.cpp

@@ -503,7 +503,7 @@ static int process_command_args(const commandline_options& cmdline_opts)
 		srand(*cmdline_opts.rng_seed);
 	}
 
-	if(cmdline_opts.screenshot || cmdline_opts.render_image) {
+	if(cmdline_opts.render_image) {
 		SDL_setenv("SDL_VIDEODRIVER", "dummy", 1);
 	}