[svg] fix rotation in svg

masque/file/svg.py

@@ -10,11 +10,26 @@ import svgwrite     # type: ignore
 
 from .utils import mangle_name
 from .. import Pattern
+from ..utils import rotation_matrix_2d
 
 
 logger = logging.getLogger(__name__)
 
 
+def _ref_to_svg_transform(ref) -> str:
+    linear = rotation_matrix_2d(ref.rotation) * ref.scale
+    if ref.mirrored:
+        linear = linear @ numpy.diag((1.0, -1.0))
+
+    a = linear[0, 0]
+    b = linear[1, 0]
+    c = linear[0, 1]
+    d = linear[1, 1]
+    e = ref.offset[0]
+    f = ref.offset[1]
+    return f'matrix({a:g} {b:g} {c:g} {d:g} {e:g} {f:g})'
+
+
 def writefile(
         library: Mapping[str, Pattern],
         top: str,
@@ -107,7 +122,7 @@ def writefile(
             if target is None:
                 continue
             for ref in refs:
-                transform = f'scale({ref.scale:g}) rotate({ref.rotation:g}) translate({ref.offset[0]:g},{ref.offset[1]:g})'
+                transform = _ref_to_svg_transform(ref)
                 use = svg.use(href='#' + mangle_name(target), transform=transform)
                 svg_group.add(use)
 

masque/test/test_svg.py

@@ -0,0 +1,70 @@
+from pathlib import Path
+import xml.etree.ElementTree as ET
+
+import numpy
+import pytest
+from numpy.testing import assert_allclose
+
+pytest.importorskip("svgwrite")
+
+from ..library import Library
+from ..pattern import Pattern
+from ..file import svg
+
+
+SVG_NS = "{http://www.w3.org/2000/svg}"
+XLINK_HREF = "{http://www.w3.org/1999/xlink}href"
+
+
+def _child_transform(svg_path: Path) -> tuple[float, ...]:
+    root = ET.fromstring(svg_path.read_text())
+    for use in root.iter(f"{SVG_NS}use"):
+        if use.attrib.get(XLINK_HREF) == "#child":
+            raw = use.attrib["transform"]
+            assert raw.startswith("matrix(") and raw.endswith(")")
+            return tuple(float(value) for value in raw[7:-1].split())
+    raise AssertionError("No child reference found in SVG output")
+
+
+def test_svg_ref_rotation_uses_correct_affine_transform(tmp_path: Path) -> None:
+    lib = Library()
+    child = Pattern()
+    child.polygon("1", vertices=[[0, 0], [1, 0], [0, 1]])
+    lib["child"] = child
+
+    top = Pattern()
+    top.ref("child", offset=(3, 4), rotation=numpy.pi / 2, scale=2)
+    lib["top"] = top
+
+    svg_path = tmp_path / "rotation.svg"
+    svg.writefile(lib, "top", str(svg_path))
+
+    assert_allclose(_child_transform(svg_path), (0, 2, -2, 0, 3, 4), atol=1e-10)
+
+
+def test_svg_ref_mirroring_changes_affine_transform(tmp_path: Path) -> None:
+    base = Library()
+    child = Pattern()
+    child.polygon("1", vertices=[[0, 0], [1, 0], [0, 1]])
+    base["child"] = child
+
+    top_plain = Pattern()
+    top_plain.ref("child", offset=(3, 4), rotation=numpy.pi / 2, scale=2, mirrored=False)
+    base["plain"] = top_plain
+
+    plain_path = tmp_path / "plain.svg"
+    svg.writefile(base, "plain", str(plain_path))
+    plain_transform = _child_transform(plain_path)
+
+    mirrored = Library()
+    mirrored["child"] = child.deepcopy()
+    top_mirrored = Pattern()
+    top_mirrored.ref("child", offset=(3, 4), rotation=numpy.pi / 2, scale=2, mirrored=True)
+    mirrored["mirrored"] = top_mirrored
+
+    mirrored_path = tmp_path / "mirrored.svg"
+    svg.writefile(mirrored, "mirrored", str(mirrored_path))
+    mirrored_transform = _child_transform(mirrored_path)
+
+    assert_allclose(plain_transform, (0, 2, -2, 0, 3, 4), atol=1e-10)
+    assert_allclose(mirrored_transform, (0, 2, 2, 0, 3, 4), atol=1e-10)