[Freeciv-Dev] (PR#2408) Problem with diagonal roads and rails

["Guest via RT" <rt@xxxxxxxxxxxxxx>]

I will describe the issue for non-isometric tilesets, but I believe the 
same problem and solution would apply to isometric tilesets as well.

Diagonal roads and rails are only drawn in two tiles - there should be 
two tiny little "corners" on the tiles it passes between.

See also this thread in the FreeCiv forum on Apolyton.net, where I have 
been working on a "bigtrident" tileset with 60x60 pixel tiles.  Due to 
the size of the tiles, this problem is a lot more noticable than with 
existing 30x30 tiles.

http://apolyton.net/forums/showthread.php?s=&threadid=66549

In particular, this diagram (which should also be attached to this 
report):

http://apolyton.net/forums/attachment.php?s=&postid=1440347

In order to deal with diagonal railways, we need just four new tiles - 
all transparent except for a little bit of railway in a corner. The 
existing code already makes a railway tiles by overlaying multiple 
railway tiles - so adding up to four more images shouldn't hurt.

i.e. add four tiles:

rail_passing_ne_corner
rail_passing_se_corner
rail_passing_sw_corner
rail_passing_nw_corner

If these are not defined in a tileset, then use nothing.

Something similar could be done for isometric tiles.

The diagram should show what I mean - the grey grid is meant to be a 4 
by 3 section of map, and the black parallel lines are railways.

The bits in red are what we need to add to make the diagonal railways 
look better. In the case of the tile in the middle of the loop, this 
can be acheived by combining the three new tiles 
rail_passing_se_corner, rail_passing_sw_corner and 
rail_passing_nw_corner.

The same applies to roads, we need four more new tiles:

road_passing_ne_corner
road_passing_se_corner
road_passing_sw_corner
road_passing_nw_corner

Peter (maubp)