On Thu, Mar 31, 2011 at 6:21 PM, Charles Galpin <[email protected]> wrote:
> I made a stylesheet that rendered linestrings quite nicely with solid colors 
> (showing congestion on roads). I drew a thicker line in black below the 
> colored line and used a round line cap to give them a nice look.
>
> We'll these lines have the drawback that they cover the road details below 
> them, like the road names, and I have been asked to make them 
> semi-transparant.
>
> However once you start reducing the opacity things like drawing two lines 
> over each other stop working well, and the end caps overlap and produce 
> darker spots. If I change the line stroke-linecap to butt, and 
> stroke-linejoin to miter but I see small gaps between them, especially on 
> corners.
>
> If anyone has some general advice on this, please let me know, otherwise my 
> specific questions are
>
> 1. Is there an opacity setting I am not seeing for the linecaps perhaps?
>
> 2. What combinations of options will give me a nice style at the ends of 
> lines that don't meet others, but meet flush with adjoining lines without 
> gaps or overlaps? I'd settle for flat line ends if the rest of the joints 
> looked good.

If you use any graphic software to draw two translucent lines one on top of the
other you'll get exactly the effect you're mentioning.
That's simply how translucency works, there is nothing we can do about
it as far as I know.

I can imagine ways to avoid that effect applying some image processing
tecniques, but they would
be hard to implement and would slow down the rendering a bit and would
require more memory too.

Cheers
Andrea


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