Make middle click scrolling based on movement distance not screen centre.

changelog

@@ -82,6 +82,8 @@ Version 1.11.7+dev:
    * Hide eras menu in MP Create for campaigns which have
      "allow_era_choice=no".
    * Introduced side's name in MP Connect.
+   * Middle click scrolling is now based on distance from initial click instead
+     of the centre of the screen.
  * WML engine:
    * WML variable turn_number is set correctly (to 1) in prestart and start
      events.  Previously, it retained its last value from the previous scenario

players_changelog

@@ -55,6 +55,8 @@ Version 1.11.7+dev:
      will need to do so again.
    * Added possibility to hide eras menu for campaigns in MP Create.
    * Introduced side's name in MP Connect.
+   * Middle click scrolling is now based on distance from initial click instead
+     of the centre of the screen.
 
 
 Version 1.11.7:

src/controller_base.cpp

@@ -20,6 +20,8 @@
 #include "game_preferences.hpp"
 #include "log.hpp"
 #include "mouse_handler_base.hpp"
+#include "resources.hpp"
+#include "play_controller.hpp"
 
 #include <boost/foreach.hpp>
 
@@ -171,18 +173,15 @@ bool controller_base::handle_scroll(CKey& key, int mousex, int mousey, int mouse
 		dx += scroll_speed;
 	}
 	if ((mouse_flags & SDL_BUTTON_MMASK) != 0 && preferences::middle_click_scrolls()) {
+		map_location original_loc = resources::controller->get_mouse_handler_base().get_scroll_start();
+		
 		const SDL_Rect& rect = get_display().map_outside_area();
 		if (point_in_rect(mousex, mousey,rect)) {
-			// relative distance from the center to the border
-			// NOTE: the view is a rectangle, so can be more sensible in one direction
-			// but seems intuitive to use and it's useful since you must
-			// more often scroll in the direction where the view is shorter
-			const double xdisp = ((1.0*mousex / rect.w) - 0.5);
-			const double ydisp = ((1.0*mousey / rect.h) - 0.5);
-			// 4.0 give twice the normal speed when mouse is at border (xdisp=0.5)
-			int speed = 4 * scroll_speed;
-			dx += round_double(xdisp * speed);
-			dy += round_double(ydisp * speed);
+			// Scroll speed is proportional from the distance from the first
+			// middle click and scrolling speed preference.
+			double speed = 0.02 * scroll_speed;
+			dx += speed * (mousex - original_loc.x);
+			dy += speed * (mousey - original_loc.y);
 		}
 	}
 

src/controller_base.hpp

@@ -115,7 +115,6 @@ protected:
 	bool browse_;
 	bool scrolling_;
 	joystick_manager joystick_manager_;
-
 };
 
 

src/mouse_handler_base.cpp

@@ -157,6 +157,8 @@ void mouse_handler_base::mouse_press(const SDL_MouseButtonEvent& event, const bo
 		}
 	} else if (is_middle_click(event)) {
 		if (event.state == SDL_PRESSED) {
+			set_scroll_start(event.x, event.y);
+			
 			map_location loc = gui().minimap_location_on(event.x,event.y);
 			minimap_scrolling_ = false;
 			if(loc.valid()) {

src/mouse_handler_base.hpp

@@ -134,6 +134,12 @@ public:
 	 */
 	virtual void right_mouse_up(int x, int y, const bool browse);
 
+	/**
+	 * Called when the middle click scrolling
+	 */
+	void set_scroll_start (int x, int y) { scroll_start_x_ = x; scroll_start_y_ = y; }
+	const map_location get_scroll_start () { return map_location(scroll_start_x_, scroll_start_y_); }
+
 protected:
 	void cancel_dragging();
 	void clear_dragging(const SDL_MouseButtonEvent& event, bool browse);
@@ -161,6 +167,10 @@ protected:
 
 	/** Show context menu flag */
 	bool show_menu_;
+	
+	/** Relative to middle click scrolling */
+	int scroll_start_x_;
+	int scroll_start_y_;
 };
 
 } // end namespace events