[Matplotlib-devel] Internals of smooth plotting in matplotlib

[Dmitri Priimak]

On Mon, May 6, 2019 at 10:10 AM Chris Barker - NOAA Federal <
chris.barker at noaa.gov> wrote:

> Now I want to plot smooth plot using these points. If I just plot
> corresponding pixels I might have wholes in the image if I zoom in,
>
>
> You really don’t want to do that.
>
> so that it is not good. If I just poly line (there is such function in
> java Graphics2D object) based on these points I have another problem. I
> have to convert each point into onscreen pixel coordinates (I can use
> floor(..)
>
>
> I would use round(), but still, drawing in pixel coordinates will result
> in somewhat jagged lines.
>
> The way around that is to use “antialiased” drawing. I would be shocked if
> there wasn’t a Java lib for that.
>

There is but it does not seem to work very well. Certainly not as good as
AGG back end.


> Most MPL back-ends use the antigrain library (AGG) which is s particularly
> good renderer, but any antialiasing renderer should be pretty good.
>

I see that now. I don't really want to depend on AGG. Perhaps I can
re-implement it in Java/Scala.


>
> You also mention zooming — make sure you zoom before converting to pixel
> coords as well.
>

Yes, I am doing just that.


> HTH,
>
> -CHB
>
>
>
> or rounding to the nearest int when doing it). And that results in jagged
> step like line that  you can see here
>
> https://i.imgur.com/t26WDut.png
>
> That does not happen in matplotlib when let say using fig.plot(...)
> function. Output is always smooth which is what I want as well. Is there a
> particular place in code where I can see how that is done?
>
> --
> Dmitri Priimak
>
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