viewbox values get rounded to nearest int

[RiedleroD]

Not much to explain here, the issue is quite simple. I hope the fix will be simple too 🤞🏻 I've attached some renders of a test image. I tested in resvg 0.41 and 0.43

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1.5 1.5">
	<rect fill="green" width="1.7" height="1.7"/>
	<rect fill="blue" width="1.5" height="1.5"/>
	<rect fill="red" width="1.2" height="1.2"/>
</svg>

Impl	Image	viewbox size	command
Your Browser		-	-
rsvg		1.5x1.5	rsvg-convert test.svg -w 100 -o test_rsvg.png
inkscape		1.5x1.5	inkscape "/home/riedler/Downloads/test.svg" --export-filename="test_inkscape.png" -w 100
resvg		2x2	resvg test.svg -w 100 test_resvg.png

note that this is less of an issue when rounded up, but quite a big issue when rounded down, since some SVGs are perfectly cut to their contents. I feel that a suitable hotfix would be always rounding up, and cutting the resulting bitmap image to the proper size afterwards.

I didn't test whether aspect ratio is preserved e.g. when viewBox="0 0 1.5 2", but I assume that's also an issue.

[RazrFalcon]

Not sure if the SVG spec specifies this behavior to begin with. Will see what we can do about it.

[RiedleroD]

I would say so, considering what they say here: https://www.w3.org/TR/SVG11/types.html#Precision

edit: equivalent SVG 2 spec: https://www.w3.org/TR/SVG2/types.html#Precision

[RazrFalcon]

Yes, I'm familiar with it, but it doesn't describe that case in particular.
Once again, I will look into it eventually.

[jermy]

Just to quickly comment - this is a specific issue with the resvg binary, and shouldn't be an issue if you use the the C or Rust API directly.

It's easy enough to change to support floating point sizes returned for the SVG, but for consistent behaviour will require a small modification to tiny-skia to support scale_by, scale_to_width and scale_to_height against the Size type (which currently only exist on it uses IntSize).

I've got those patches - let me know if it's worth doing a couple of respective PRs for this.

[jermy]

In the spirit of pushing stashed things upstream rather than lose them; I've created PRs for tiny-skia #146 and #875 that contain what I mentioned I'd previously done.

I have no idea how much appetite for a change like this in resvg, but @RiedleroD here it is if you wanted to pull these changes into local versions of resvg/tiny-skia and try it out.