[Freeciv-Dev] Re: (PR#7297) Caching map canvas

["Vasco Alexandre da Silva Costa" <vasc@xxxxxxxxxxxxxx>]

<URL: http://rt.freeciv.org/Ticket/Display.html?id=7297 >

On Fri, 23 Jan 2004, Raimar Falke wrote:

>
> <URL: http://rt.freeciv.org/Ticket/Display.html?id=7297 >
>
>
> Idea: have a backing store of the size of map which contains the whole
> drawn into it.
>
> Purpose: allow fast changing of the mapview origin by just copying
> relevant parts of the backing store to the screen in the right places.
>
> You have the problem of wrapping (after the eastmost tile comes the
> westmost one). But this is easy for non-iso tilesets. Non-iso tilesets
> have another advantage: they have no overlapping between tiles.
>
> For iso tilesets the idea is to have a larger backing store. 9 times
> the place required for drawing the complete map. So around the primary
> instance of the map in the backing store you place 8 other copies of
> it around. At the border you do the correct overlapping drawing.
>
> A little picture for the iso case:
>
>
>       a                b               c
>
>
>           +---------------+
>       d   |            e  |            f
>           |               |
>           |               |
>           +---------------+
>       g                h               i
>
> where the rectangle is the part which is drawn to the screen. And a-i
> are the instances of the map.
>
> Advantages:
>   - fast change of map origin
>   - pixel based position of the view quite easy
>
> Disadvantages:
>   - large memory usage
>   - updating of a tiles is more expensive in the iso case

Old scrolling games used these sorts of techniques. e.g. parallax
scrolling.

---
Vasco Alexandre da Silva Costa @ Instituto Superior Tecnico, Lisboa