[Freeciv-Dev] Re: (PR#6257) recodify map_pos<->index conversion to use native positions

["Jason Short" <jdorje@xxxxxxxxxxxxxxxxxxxxx>]

Gregory Berkolaiko wrote:
> On Tue, 23 Sep 2003, Jason Short wrote:
> 
> 
>>Index positions are ordered based off of native ones.  So the current 
>>conversion operations (e.g., map_pos_to_index and index_to_map_pos) are 
>>no good when we start using native positions.
>>
>>Unfortunately going through native coordinates requires an intermediate 
>>pair of variables, which is a problem with macros.  There are three 
>>possible solutions:
> 
> 
> How about introducing 2 new macros
>       map_to_native_x
>       map_to_native_y
> ?

Clever.  This is generally the type of thing we want to avoid - since 
most of the time it will only lead to misuse - but here it is helpful.

Patch attached.

Note that for for iso-maps the calculation will be something like

   y: (map_x + map_y - map.xsize)
   x: (map_x - map_y + map.xsize - (map_x + map_y - map.xsize) & 1) / 2

which is why both map x and y values are needed for the macros (which is 
why taking them individually is generally a bad idea).

I used map_pos_to_native_[xy] for the names - along the lines of 
map_pos_to_index.  Making them longer discourages people from using them 
needlessly :-).

jason

? rc
Index: common/map.h
===================================================================
RCS file: /home/freeciv/CVS/freeciv/common/map.h,v
retrieving revision 1.153
diff -u -r1.153 map.h
--- common/map.h        2003/09/19 13:17:12     1.153
+++ common/map.h        2003/09/23 18:31:48
@@ -241,15 +241,20 @@
 #define map_to_native_pos(pnat_x, pnat_y, map_x, map_y) \
   (*(pnat_x) = (map_x), *(pnat_y) = (map_y))
 
+#define map_pos_to_native_x(map_x, map_y) (map_x)
+#define map_pos_to_native_y(map_x, map_y) (map_y)
+
 #define map_pos_to_index(map_x, map_y)        \
   (CHECK_MAP_POS((map_x), (map_y)),           \
-   (map_x) + (map_y) * map.xsize)
+   (map_pos_to_native_x(map_x, map_y)         \
+    + map_pos_to_native_y(map_x, map_y) * map.xsize))
 
 /* index_to_map_pos(int *, int *, int) inverts map_pos_to_index */
 #define index_to_map_pos(pmap_x, pmap_y, index) \
   (CHECK_INDEX(index),                          \
    *(pmap_x) = (index) % map.xsize,             \
-   *(pmap_y) = (index) / map.xsize)
+   *(pmap_y) = (index) / map.xsize,             \
+   native_to_map_pos(pmap_x, pmap_y, *(pmap_x), *(pmap_y)))
 
 #define DIRSTEP(dest_x, dest_y, dir)   \
 (    (dest_x) = DIR_DX[(dir)],         \