[Freeciv-Dev] Re: to wrap or not to wrap?

[Raimar Falke <hawk@xxxxxxxxxxxxxxxxxxxxxxx>]

On Wed, Oct 10, 2001 at 12:27:06PM -0400, Jason Dorje Short wrote:
> Raimar Falke wrote:
> > 
> > On Wed, Oct 10, 2001 at 11:39:19AM -0400, Jason Dorje Short wrote:
> > > Raimar Falke wrote:
> > > >
> > > > On Wed, Oct 10, 2001 at 10:34:13AM -0400, Jason Dorje Short wrote:
> 
> > > > > That is, if we limit our topologies to only those that wrap in simple
> > > > > ways, we can write a wrap_map_pos(&vx, &vy) function that will wrap 
> > > > > the
> > > > > given coordinate pair [1] independent of it's being a actual tile.  
> > > > > This
> > > > > can be used practically as-is in the current client implementation,
> > > > > although I strongly feel that this implementation is flawed and should
> > > > > be fixed anyway.
> 
> > > Like I said, it is confusing and will probably lead to misuse.
> > 
> > Usual question: who/what needs this? Note that the only wrapping
> > occurs at the GUI and even this case will be no longer if the client
> > draw each tile only one time.
> 
> AFAIK just the client.
> 
> Right now the client does only draw each tile one time.  However, it
> uses a "trick" to accomplish this:
> 
> /* x0, y0 is corner of canvas */
> /* width, height are dimensions of canvas */
> for (x=0; x<width; x++)
>   for (y=0; y<width; y++) {
>     x1 = x, y1 = y;
>     wrap_map_pos(&x1, &y1);
>     draw_tile(x0+x1, y0+y1);
>   }
> 
> See, (x1, y1) isn't an actual map position!  It's a vector representing
> the position of the tile on the map canvas.  If the canvas is wider than
> the map, then the tile *will* be drawn twice - but it'll be drawn in the
> same position so nobody notices (this could easily be avoided by
> restricting the size of the mapcanvas).  The important point, though, is
> that because (x1, y1) isn't an actual map position normalize_map_pos
> can't be used on it.
> 
> The "correct" way to do the drawing is like this, IMO:
> 
> for (x=0; x<width; x++)
>   for (y=0; y<height; y++) {
>     x1 = x0+x, y1 = y0+y;
>     if (normalize_map_pos(&x1, &y1))
>       draw_tile(x1, y1);
>     else
>       draw_black_tile(x1, y1);
>   }
> 
> This uses only mathematically correct operations on the map position. 
> In the case of the overhead view it is still easy to avoid drawing tiles
> multiple times [1] - 

> you just restrict the size of the map canvas [2]. 

What if in the above loop the width isn't the map canvas width, but
the map.xsize? It should be fine if you blank all tiles before.

> In the case of the isometric view the math would be harder but it would
> still be possible.
> 
> Gaute pointed out before that it doesn't matter which set of coordinates
> you choose to be proper/normal - it's just a convenience to make
> everything happen within map.xsize/map.ysize.  Mathematically this is
> correct, but wrap_map_pos is not mathematically clean - the client MUST
> have each vector returned by wrap_map_pos be exactly correct.
> 
> [1] Personally, I would prefer to have tiles drawn multiple times.  But
> that's just me...

If it is cleaner what is needed for one-drawing and what for the
multiple drawing I don't have a problem. This can be a compile or
run-time constant. However it looks to me that the easier goal of the
next step is the one-time draw solution.

> [2] This really seems like the obvious solution.  Does anyone know why
> it wasn't used before?

So in overall we don't need the method you suggested?!

        Raimar

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