kicad-developers team mailing list archive

[Brian Sidebotham <brian.sidebotham@xxxxxxxxx>]

On 21 February 2012 07:25, Miguel Angel Ajo Pelayo <miguelangel@xxxxxxx> wrote:
>
>     I've been playing around with the code, and learning a little bit how
> does kicad draw everything.
>
> I'm also quite new to KiCad, and I'm getting used to work with the tool. It
> was surprising for me
> that the layers are painted using GR_OR operation.
>
> Is it implemented this way because you find it more clear to work this way?
> or is it implemented
> this way to simplify (/speedup) the drawing process?
>
> For me, it would seem nicer (may be it's just what I'm used to):
>
>   Drawing without OR/XOR/etc, just drawing, in order:
>
>    1) tracks bottom-up for all the layers (excluding: current one, and
> current overlay one)
>    2) tracks of the current layer
>    3) the current overlay (current overlay = nearest one to the current
> layer)
>    4) vias, pads, etc.
>
> It must be a little bit more time consuming, since (in plain implementation)
> we may need to
> iterate all over the lists at least 3 times (1,2,3). Better implementation
> could be done
> with a little more of memory usage.
>
>
>     If it's something that the project finds interesting, I could be doing
> it. Even if there is a 50%/50% and
> the code could be done in such way that doesn't become harder to maintain,
> also both modes could be kept.
>
>
>     Cheers,
>
> --
>
> Miguel Angel Ajo Pelayo
> http://www.nbee.es
> +34 636 52 25 69
> skype: ajoajoajo

Hi Miguel,

The drawing code is as it is in order to efficient whilst allowing the
layers to be visible through each other. For example, where a Front
track crosses over a Back track we would see the OR'd result of the
two layer colours where they cross. This is a very handy feature - I
have only ever known PCB layout packages to use this method of
compositing the view. Nowadays though transparency is generally used
instead.

See Torsten's work on a Graphics Abstracion Layer for KiCad:
https://code.launchpad.net/~kicad-testing-committers/kicad/kicad-gal

Best Regards,

Brian.