new plugin: decrease accuracy of floating-point numbers

[deepsweet]

like in convertPathData plugin but at least for polyline and polygon data.

but if the default width/height are very small then increase the accuracy or do something else to reduce distortion.

[GreLI]

SVG allows relative coordinates, so it's important to avoid a systematic error by accumulation rounding errors from the every coordinate. I believe the rounding procedure should work with absolute coordinates. So, the conversion must be done before the rounding.

[deepsweet]

you're right, and that's how it happens in the existing convertPathData plugin.
first - convert absolute to relative, and only then - floating-point numbers rouding.

but there is a problem with the absolute->relative convertion that is not dependent on svgo own rounding - some browsers rounds relative coordinates calculation in their own way, and as a result it's impossible to get a "pixel lossless" optimization.

[GreLI]

No, no, no. I was saying quite opposite: first, convert to absolute if needed, then round the values, and then you can convert back to the relative. Otherwise the error will be accumulated on each path step.

[deepsweet]

oh, now i understand.

thank you, i'll keep it in mind :)