Added Proof-of-concept of the new background still has some flaws

* upon scrolling the background static (so maps scrolls over wood)

* _off^usr has redraw glitches since background is only updated every
  now and then

* the alpha at the border tends to "build up"

* we impose a huge performance hit

The code still needs a lot of work, but what needs to be done heavily
depends on whether or not the half-hexes are reintroduced so that the
is postponed until that descission has been made.

changelog

@@ -33,6 +33,8 @@ Version 1.3.3+svn:
    * reduced "sea sickness" effect when scrolling at accelerated speed
    * allow to select item in menu with right-click 
    * right-click outside of a cancelable dialog to close it
+   * added experimental new background read comment before draw_background()
+     in display.cpp
  * Miscellaneous and bugfixes
    * fix bug #4299: word wrap for menus with very long option strings
    * various bugfixes and code cleanups

data/core/terrain-graphics/_final.cfg

@@ -854,4 +854,6 @@
 {TERRAIN_ADJACENT          -560    Chw              (!,Chw,Chr)                          water/coast}
 {TERRAIN_ADJACENT          -570    (!,Chr,Chw)      Chr                                  flat/grass}
 
+{TERRAIN_BASE       _off^*                 off-map/alpha}
+
 {TERRAIN_BASE_DEFAULT void}

players_changelog

@@ -25,6 +25,9 @@ Version 1.3.3+svn:
      an image of a new scenario immediately before entering it, is now only
      presented if the game was built with TINY_GUI.  Non-tiny systems do this
      automatically without asking.
+   * Added a new experimental background, this is under evaluation but causes
+     a rather severe performance penalty especially while scrolling. This will
+     be fixed once the decission of the final version has been made.
 
   * Unit changes and balancing
 

src/display.cpp

@@ -70,7 +70,7 @@ display::display(unit_map& units, CVideo& video, const gamemap& map,
 	screen_(video), xpos_(0), ypos_(0),
 	zoom_(DefaultZoom), map_(map), units_(units),
 	temp_unit_(NULL),
-	minimap_(NULL), redrawMinimap_(false),
+	minimap_(NULL), redrawMinimap_(false), redraw_background_(true),
 	status_(status),
 	teams_(t), nextDraw_(0),
 	invalidateAll_(true), invalidateUnit_(true),
@@ -502,6 +502,7 @@ void display::scroll(int xmove, int ymove)
 	_scroll_event.notify_observers();
 	update_rect(map_area());
 
+	redraw_background_ = true;
 	redrawMinimap_ = true;
 }
 
@@ -536,6 +537,7 @@ void display::set_zoom(int amount)
 		energy_bar_rects_.clear();
 		image::set_zoom(zoom_);
 		map_labels_.recalculate_labels();
+		redraw_background_ = true;
 		invalidate_all();
 
 		// Forces a redraw after zooming. This prevents some graphic glitches from occurring.
@@ -786,6 +788,8 @@ void display::redraw_everything()
 
 	map_labels_.recalculate_labels();
 
+	redraw_background_ = true;
+
 	invalidate_all();
 	draw(true,true);
 }
@@ -902,6 +906,34 @@ static void draw_label(CVideo& video, surface target, const theme::label& label)
 	update_rect(loc);
 }
 
+/**
+ * Proof-of-concept of the new background still has some flaws
+ * * upon scrolling the background static (so maps scrolls over wood)
+ * * _off^usr has redraw glitches since background is only updated every now and then
+ * * the alpha at the border tends to "build up"
+ * * we impose a huge performance hit
+ *
+ * needs quite some work to become fully working, but first evaluate whether
+ * the new way is really wanted.
+ */
+static void draw_background(surface screen, const SDL_Rect& area)
+{
+	static const surface wood(image::get_image("terrain/off-map/wood.png",image::UNSCALED));
+	static const unsigned int width = wood->w;
+	static const unsigned int height = wood->h;
+	wassert(!wood.null());
+
+	const unsigned int w_count = static_cast<int>(ceil(static_cast<double>(area.w) / static_cast<double>(width)));
+	const unsigned int h_count = static_cast<int>(ceil(static_cast<double>(area.h) / static_cast<double>(height)));
+
+	for(unsigned int w = 0, w_off = area.x; w < w_count; ++w, w_off += width) {
+		for(unsigned int h = 0, h_off = area.y; h < h_count; ++h, h_off += height) {
+			SDL_Rect clip = {w_off, h_off, 0, 0};
+			SDL_BlitSurface(wood, NULL, screen, &clip);
+		}
+	}
+}
+
 void display::draw(bool update,bool force)
 {
 	bool changed = false;
@@ -935,6 +967,19 @@ void display::draw(bool update,bool force)
 		changed = true;
 	}
 
+	if(redraw_background_) {
+		// full redraw of the background
+		const SDL_Rect clip_rect = map_outside_area();
+		const surface outside_surf(screen_.getSurface());
+		clip_rect_setter set_clip_rect(outside_surf, clip_rect);
+		draw_background(outside_surf, clip_rect);
+
+		redraw_background_ = false;
+
+		// force a full map redraw
+		invalidateAll_ = true;
+	}
+
 	if(invalidateAll_ && !map_.empty()) {
 		INFO_DP << "draw() with invalidateAll\n";
 		gamemap::location topleft;
@@ -1939,7 +1984,7 @@ std::vector<surface> display::get_terrain_images(const gamemap::location &loc,
 	} else if(terrain_type == ADJACENT_BACKGROUND){
 		// this should only happen with the off map tiles and now 
 		// return the void image. NOTE this is a temp hack
-		const surface surface(image::get_image(game_config::void_image));
+		const surface surface(image::get_image("terrain/off-map/alpha.png"));
 		wassert(!surface.null());
 		if (!surface.null()) {
 			res.push_back(surface);

src/display.hpp

@@ -478,6 +478,7 @@ private:
 
 	surface minimap_;
 	bool redrawMinimap_;
+	bool redraw_background_;
 
 	paths::route route_;