Use Inkscape to export your file to PNG.
Open the PNG in Gimp and export it to a variety of file formats.
Currently, the 2.10 export dialog box does not show the file types dialog. But if you type the correct file extension, you will have the specific dialog box for that file type.
OK, so this is what I have worked out.
Slices will automatically be ordered from left to right yes but the image doesnt have to be upright.
So for a film reel example where I want columns and slices going vertically down then right ...
Rotate the image. So my picture is now on its side and the slices run along the length meaning when I cut them it will have ...