Nested <svg> width/height with decimal values are truncated to integers, mis-scaling and mis-positioning embedded content

[Watremez]

Description

When a nested <svg> element declares non-integer width/height (e.g. width="5.8"), the fractional part is silently dropped. The nested content is then scaled from the truncated value, so it renders smaller than expected and appears shifted towards the top-left of its intended box (the x/y position is parsed as Float and stays correct, only the scale is wrong).

My real-world case is a QR code with a logo embedded as a nested <svg> sized in QR-module units (width="5.8" on a 29-module grid): the logo renders off-center inside the QR.

Minimal reproduction

The tomato circle is sized to exactly fill the blue-stroked square:

<svg xmlns="http://www.w3.org/2000/svg" width="200" height="200" viewBox="0 0 10 10">
  <rect width="10" height="10" fill="#eeeeee"/>
  <rect x="2.1" y="2.1" width="5.8" height="5.8" fill="none" stroke="#0000ff" stroke-width="0.1"/>
  <svg x="2.1" y="2.1" width="5.8" height="5.8" viewBox="0 0 100 100">
    <circle cx="50" cy="50" r="48" fill="#ff6347"/>
  </svg>
</svg>

Expected: the circle fills the blue square (scale = 5.8/100) — this is how Safari, Chrome and librsvg render it.

Actual with SwiftDraw: the circle is rendered at 5/100 scale (~86% of the expected size), anchored at the top-left of the square.

Cause

DOM.Length is an integer type, and the parsed floating-point dimension is truncated when the DOM.SVG is built:

• DOM/Sources/DOM.swift#L39 — typealias Length = Swift.Int
• DOM/Sources/Parser.XML.SVG.swift#L57 — DOM.SVG(width: DOM.Length(w), height: DOM.Length(h)) where w/h are Float (5.8 → 5)

The truncated value then feeds the nested-svg transform in LayerTree.Builder.makeTransform (sx = width / viewBox.width → 5/320 instead of 5.8/320 in my real case).

Per the SVG spec, width/height are <length> values and may be fractional.

Environment

• SwiftDraw 0.29.0 (also present on main at the time of writing)
• Reproduced with swiftdrawcli repro.svg --format png and with SVGView(svg:) on iOS 26

Workaround

Replacing the nested <svg x y width height viewBox> with <g transform="translate(…) scale(…)"> avoids the truncation, since transform values are parsed as Float.