Postby Xav » Sun Oct 08, 2017 7:00 pm
It seems a little rude to dismiss Brynn's reply with "Literally everything that a computer program does is maths!". By that argument I want to know why I can't calculate the trajectory of the Voyager 1 probe by playing Pacman. After all, it's all maths, right?
The point I think she was trying to make is that the algorithm used for the Fill tool is largely bitmap based, not vector based. Still maths, but a different subset of the field. The Fill tool essentially performs the same job as the bucket fill in a bitmap editor, but then converts the resultant collection of pixels to a vector. It's a bit like exporting your image as a PNG, loading it into a bitmap editor, filling a region, importing it back into Inkscape then running Trace Bitmap on the filled area.
It's not a mathematically precise tool, but it is computationally cheap. And because it works on the pixels of a bitmap representation of your image, the end result depends on the resolution of that bitmap - which is why zooming has an effect. In my opinion it's only really of any use for filling the outline artwork of comic strips and similar - and even then (as I know from experience) it can still require a lot of manual cleaning up to get the desired result.
For most vector work it's best avoided. If you want mathematically accurate (or, at least, more accurate) shapes then you should be using boolean operations to create your path instead.