[Freeciv-Dev] Re: (PR#4004) A canvas_iterate macro for mapview

["Jason Short" <jdorje@xxxxxxxxxxxxxxxxxxxxx>]

Jason Short wrote:
> I would like to write a new macro, canvas_iterate, to the mapview code. 
>   The interface is
> 
>    canvas_iterate(canvas_x0, canvas_y0, width, height, x_itr, y_itr)
> 
> and it iterates over the mapview canvas, *in map coordinates*.

I believe this one works, although it's difficult to see why.  Although 
it is extremely complicated, it isn't too much worse than the current 
show_city_descriptions iteration - and certainly better than it would be 
if such an iteratation were used in 10 places throughout the code...

jason

#define canvas_iterate(canvas_x0, canvas_y0, width, height, map_x, map_y)   \
{                                                                           \
  int _gui_x, _gui_y;                                                       \
  int _gui_width, _gui_height;                                              \
  int _my_width = width + NORMAL_TILE_WIDTH - 1;                            \
  int _my_height = height + NORMAL_TILE_HEIGHT - 1;                         \
  int _my_canvas_x0 = canvas_x0, _my_canvas_y0 = canvas_y0;                 \
  if (is_isometric) {                                                       \
    _my_canvas_x0 -= NORMAL_TILE_WIDTH / 2 - 1;                             \
    _my_canvas_y0 -= NORMAL_TILE_HEIGHT / 2 - 1;                            \
    _my_width += NORMAL_TILE_WIDTH - 2;                                     \
    _my_height += NORMAL_TILE_HEIGHT - 2;                                   \
  }                                                                         \
  _gui_width = _my_width / NORMAL_TILE_WIDTH;                               \
  if (is_isometric) {                                                       \
    _gui_height = 2 * _my_height / NORMAL_TILE_HEIGHT;                      \
  } else {                                                                  \
    _gui_height = _my_height / NORMAL_TILE_HEIGHT;                          \
  }                                                                         \
  for (_gui_x = 0; _gui_x < _gui_width; _gui_x++) { /* native x */          \
    for (_gui_y = 0; _gui_y < _gui_height; _gui_y++) { /* native y */       \
      int _gx = 2 * _gui_x + (is_isometric ? (_gui_y & 1) : 0); /* ntl x */ \
      int _gy = is_isometric ? _gui_y : (2 * _gui_y); /* ntl y */           \
      int _canvas_x = _my_canvas_x0 + _gx * NORMAL_TILE_WIDTH / 2;          \
      int _canvas_y = _my_canvas_y0 + _gy * NORMAL_TILE_HEIGHT / 2;         \
      int map_x, map_y;                                                     \
      if (_canvas_x > canvas_x0 - NORMAL_TILE_WIDTH                         \
          && _canvas_y > canvas_y0 - NORMAL_TILE_HEIGHT                     \
          && _canvas_x <= canvas_x0 + width                                 \
          && _canvas_y <= canvas_y0 + height                                \
          && canvas_to_map_pos(&map_x, &map_y, _canvas_x, _canvas_y)) {