vehicle part descriptions: handle overflow and scrolling

change vpart_info::format_description to count the number of lines
printed and return that value.

change vehicle:print_vparts_desc to count the number of lines it is
printing versus the window size, and to add scroll messages if the
there are more lines of description than available space. Add an offset,
so the descriptions don't always start printing at the frame part.

adjust veh_interact::do_main_loop to add the keybinds for scrolling
through the descriptions.

incidentally, in veh_interact::move_cursor, correctly pass the size of
w_msg so descriptions get line wrapped to the width of the window and not
the height.

data/raw/keybindings.json

@@ -1897,6 +1897,24 @@
             { "input_method":"keyboard", "key":"TAB" }
         ]
     },
+    {
+        "type" : "keybinding",
+        "id": "DESC_LIST_UP",
+        "category": "VEH_INTERACT",
+        "name": "Scroll up through vehicle part descriptions",
+        "bindings":[
+            { "input_method":"keyboard", "key":"<" }
+        ]
+    },
+    {
+        "type" : "keybinding",
+        "id": "DESC_LIST_DOWN",
+        "category": "VEH_INTERACT",
+        "name": "Scroll down through vehicle part descriptions",
+        "bindings":[
+            { "input_method":"keyboard", "key":">" }
+        ]
+    },
     {
         "type" : "keybinding",
         "id": "TOGGLE_UNAVAILABLE_CONSTRUCTIONS",

src/veh_interact.cpp

@@ -176,6 +176,8 @@ veh_interact::veh_interact( vehicle &veh, int x, int y )
     main_context.register_action("RELABEL");
     main_context.register_action("FUEL_LIST_DOWN");
     main_context.register_action("FUEL_LIST_UP");
+    main_context.register_action("DESC_LIST_DOWN");
+    main_context.register_action("DESC_LIST_UP");
     main_context.register_action("CONFIRM");
     main_context.register_action("HELP_KEYBINDINGS");
     main_context.register_action("FILTER");
@@ -318,6 +320,10 @@ void veh_interact::do_main_loop()
         } else if ( action == "FUEL_LIST_UP" ) {
             move_fuel_cursor( -1 );
             move_cursor( 0, 0 );
+        } else if ( action == "DESC_LIST_DOWN" ) {
+            move_cursor( 0, 0, 1 );
+        } else if ( action == "DESC_LIST_UP" ) {
+            move_cursor( 0, 0, -1 );
         }
         if ( sel_cmd != ' ' ) {
             finish = true;
@@ -1566,14 +1572,20 @@ bool veh_interact::can_potentially_install(const vpart_info &vpart)
  * Moves the cursor on the vehicle editing window.
  * @param dx How far to move the cursor on the x-axis.
  * @param dy How far to move the cursor on the y-axis.
+ * @param dstart_at How far to change the start position for vehicle part descriptions
  */
-void veh_interact::move_cursor( int dx, int dy )
+void veh_interact::move_cursor( int dx, int dy, int dstart_at )
 {
     const int hw = getmaxx( w_disp ) / 2;
     const int hh = getmaxy( w_disp ) / 2;
 
     ddx += dy;
     ddy -= dx;
+    if( dx || dy ) {
+       start_at = 0;
+    } else {
+       start_at += dstart_at;
+    }
 
     display_veh();
     // Update the current active component index to the new position.
@@ -1598,7 +1610,7 @@ void veh_interact::move_cursor( int dx, int dy )
     wrefresh( w_parts );
 
     werase( w_msg );
-    veh->print_vparts_descs( w_msg, getmaxy( w_msg ), cpart );
+    veh->print_vparts_descs( w_msg, getmaxy( w_msg ), getmaxx( w_msg ), cpart, start_at );
     wrefresh( w_msg );
 
     can_mount.clear();

src/veh_interact.h

@@ -55,6 +55,7 @@ class veh_interact
 
         int ddx = 0;
         int ddy = 0;
+        int start_at = 0;
         const vpart_info *sel_vpart_info = nullptr;
         char sel_cmd = ' '; //Command currently being run by the player
 
@@ -92,7 +93,7 @@ class veh_interact
                           const std::map<skill_id, int> &skills, int moves ) const;
 
         int part_at( int dx, int dy );
-        void move_cursor( int dx, int dy );
+        void move_cursor( int dx, int dy, int dstart_at = 0 );
         task_reason cant_do( char mode );
         bool can_potentially_install( const vpart_info &vpart );
         /** Move index (parameter pos) according to input action:

src/veh_type.cpp

@@ -514,9 +514,10 @@ std::string vpart_info::name() const
     return name_;
 }
 
-void vpart_info::format_description( std::ostringstream &msg, std::string format_color,
-                                     int width ) const
+int vpart_info::format_description( std::ostringstream &msg, std::string format_color,
+                                    int width ) const
 {
+    int lines = 0;
     if( ! description.empty() ) {
         msg << _( "<color_white>Description</color>\n" );
         msg << "> " << format_color;
@@ -527,6 +528,7 @@ void vpart_info::format_description( std::ostringstream &msg, std::string format
             msg << "\n  " << wrap_descrip[i];
         }
         msg << "</color>\n";
+        lines += 1 + wrap_descrip.size();
 
         // borrowed from item.cpp and adjusted
         const quality_id quality_jack( "JACK" );
@@ -539,8 +541,10 @@ void vpart_info::format_description( std::ostringstream &msg, std::string format
                                       ( int )convert_weight( qual.second * TOOL_LIFT_FACTOR ), weight_units() );
             }
             msg << ".</color>\n";
+            lines += 1;
         }
     }
+    return lines;
 }
 
 requirement_data vpart_info::install_requirements() const

src/veh_type.h

@@ -149,7 +149,8 @@ class vpart_info
         bool legacy = true;
 
         /** Format the description for display */
-        void format_description( std::ostringstream &msg, std::string format_color, int width ) const;
+        int format_description( std::ostringstream &msg, std::string format_color, int width ) const;
+
 
         /** Installation requirements for this component */
         requirement_data install_requirements() const;

src/vehicle.cpp

@@ -2889,12 +2889,12 @@ int vehicle::print_part_list( const catacurses::window &win, int y1, const int m
  * Prints a list of descriptions for all parts to the screen inside of a boxed window
  * highlighting a selected one.
  * @param win The window to draw in.
- * @param y1 The y-coordinate to start drawing at.
  * @param max_y Draw no further than this y-coordinate.
  * @param width The width of the window.
  * @param &p The index of the part being examined.
+ * @param start_at Which vehicle part to start printing at.
  */
-void vehicle::print_vparts_descs( const catacurses::window &win, int width, int &p ) const
+void vehicle::print_vparts_descs( const catacurses::window &win, int max_y, int width, int &p, int start_at ) const
 {
     if( p < 0 || p >= ( int )parts.size() ) {
         return;
@@ -2903,15 +2903,29 @@ void vehicle::print_vparts_descs( const catacurses::window &win, int width, int
     std::vector<int> pl = this->parts_at_relative( parts[p].mount.x, parts[p].mount.y );
     std::ostringstream msg;
 
-    for( size_t i = 0; i < pl.size(); i++ ) {
+    int lines = 0;
+    start_at = std::max( start_at, 0 );
+    if( start_at ) {
+           msg << "<color_yellow>" << "<  " << _( "More parts here..." ) << "</color>\n";
+           lines += 1;
+    }
+    for( size_t i = start_at; i < pl.size(); i++ ) {
         const vehicle_part &vp = parts[ pl [ i ] ];
+        std::ostringstream possible_msg;
         std::string name_color = string_format( "<color_%1$s>",
                                                 string_from_color( vp.is_broken() ? c_dark_gray : c_light_green ) );
-        msg << name_color << vp.name() << "</color>\n";
+        possible_msg << name_color << vp.name() << "</color>\n";
         std::string desc_color = string_format( "<color_%1$s>",
                                                 string_from_color( vp.is_broken() ? c_dark_gray : c_light_gray ) );
-        vp.info().format_description( msg, desc_color, width - 2 );
-        msg << "</color>\n";
+        int new_lines = 2 + vp.info().format_description( possible_msg, desc_color, width - 2 );
+        possible_msg << "</color>\n";
+        if( lines + new_lines <= max_y ) {
+           msg << possible_msg.str();
+           lines += new_lines;
+        } else {
+           msg << "<color_yellow>" << _( "More parts here..." ) << "  >" << "</color>\n";
+           break;
+        }
     }
     werase( win );
     fold_and_print( win, 0, 1, width, c_light_gray, msg.str() );

src/vehicle.h

@@ -580,7 +580,8 @@ class vehicle
                              int hl = -1 ) const;
 
         // Vehicle parts descriptions - descriptions for all the parts on a single tile
-        void print_vparts_descs( const catacurses::window &win, int width, int &p ) const;
+        void print_vparts_descs( const catacurses::window &win, int max_y, int width, int &p,
+                                 int start_at ) const;
 
     /**
      *  Operate vehicle controls