[Freeciv-Dev] Re: (PR#6356) move the origin tile of the mapview

["Jason Short" <jdorje@xxxxxxxxxxxxxxxxxxxxx>]

Jason Short wrote:

> The form that makes topology compatability easiest has the top-left 
> corner of the bounding box of the x0,y0 tile at (0,0).  Now we can align 
> both left and top sides of the mapview with a non-wrapping iso-map.  See 
> new.png (sent to RT separately).

Patch attached.

Note that it is easy to verify that this patch works.  The only two 
places that need changing are map_to_canvas_pos and canvas_to_map_pos. 
Just click around (middle-click) on various places on each tile and it's 
obvious that the two operations are inverses.

jason

Index: client/mapview_common.c
===================================================================
RCS file: /home/freeciv/CVS/freeciv/client/mapview_common.c,v
retrieving revision 1.63
diff -u -r1.63 mapview_common.c
--- client/mapview_common.c     2003/10/01 10:30:56     1.63
+++ client/mapview_common.c     2003/10/01 18:57:34
@@ -218,12 +218,10 @@
     /*
      * As the above picture shows, each isometric-coordinate unit
      * corresponds to a half-tile on the canvas.  Since the (x0, y0)
-     * tile actually has its top corner (of the diamond-shaped tile)
-     * located right at the corner of the canvas, to find the top-left
-     * corner of the surrounding rectangle we must subtract off an
-     * additional half-tile in the X direction.
+     * tile has its top-left corner located right at the corner of the
+     * canvas, the math is easy.
      */
-    *canvas_x = (iso_x - 1) * NORMAL_TILE_WIDTH / 2;
+    *canvas_x = iso_x * NORMAL_TILE_WIDTH / 2;
     *canvas_y = iso_y * NORMAL_TILE_HEIGHT / 2;
   } else {                     /* is_isometric */
     *canvas_x = map_x - mapview_canvas.map_x0;
@@ -276,8 +274,13 @@
      * only use integer math, and C integer division rounds toward zero
      * instead of rounding down.
      *
+     * canvas_x is translated so that the top corner of the origin tile
+     * will be at (0,0).  This means the origin is the top-leftmost tile
+     * that is fully shown on the canvas.
+     *
      * For another example of this math, see canvas_to_city_pos().
      */
+    canvas_x -= NORMAL_TILE_WIDTH / 2;
     *map_x = DIVIDE(canvas_x * H + canvas_y * W, W * H);
     *map_y = DIVIDE(canvas_y * W - canvas_x * H, W * H);
   } else {                     /* is_isometric */