Add test that exposes a bug, fix bug. Caught in review.

src/nanoemoji/color_glyph.py

@@ -49,7 +49,7 @@
 import pathops
 
 
-def _scale_viewbox_to_font_metrics(
+def scale_viewbox_to_font_metrics(
     view_box: Rect, ascender: int, descender: int, width: int
 ):
     assert descender <= 0
@@ -71,7 +71,7 @@ def map_viewbox_to_font_space(
 ) -> Affine2D:
     return Affine2D.compose_ltr(
         [
-            _scale_viewbox_to_font_metrics(view_box, ascender, descender, width),
+            scale_viewbox_to_font_metrics(view_box, ascender, descender, width),
             # flip y axis and shift so things are in the right place
             Affine2D(1, 0, 0, -1, 0, ascender),
             user_transform,
@@ -85,7 +85,7 @@ def map_viewbox_to_otsvg_space(
 ) -> Affine2D:
     return Affine2D.compose_ltr(
         [
-            _scale_viewbox_to_font_metrics(view_box, ascender, descender, width),
+            scale_viewbox_to_font_metrics(view_box, ascender, descender, width),
             # shift things in the [+x,-y] quadrant where OT-SVG expects them
             Affine2D(1, 0, 0, 1, 0, -ascender),
             user_transform,

src/nanoemoji/parts.py

@@ -24,6 +24,7 @@
 from functools import lru_cache, partial, reduce
 import json
 from nanoemoji.config import FontConfig
+from nanoemoji.color_glyph import scale_viewbox_to_font_metrics
 from pathlib import Path
 from picosvg.geometric_types import Rect
 from picosvg.svg import SVG
@@ -149,7 +150,10 @@ def add(self, source: PathSource):
             )
         elif isinstance(source, SVG):
             source.checkpicosvg()
-            transform = Affine2D.rect_to_rect(source.view_box(), self.view_box)
+            source_box = source.view_box()
+            transform = scale_viewbox_to_font_metrics(
+                self.view_box, source_box.h, 0, source_box.w
+            )
             shapes = tuple(s.as_path() for s in source.shapes())
         else:
             raise ValueError(f"Unknown part source: {type(source)}")

tests/parts_test.py

@@ -227,3 +227,30 @@ def test_scaled_merge_arcs_to_cubics():
         "MCCCCZ",
         "MCCCCZ",
     ), f"Path damaged\nnorm {norm}\npaths {paths}"
+
+
+def _start_at_origin(path):
+    cmd, args = next(iter(path))
+    assert cmd == "M"
+    x, y = args
+    return path.move(-x, -y)
+
+
+# SVGs with varied width that contains squares should push squares
+# into the part store, not get mangled into rectangles.
+def test_squares_stay_squares():
+    parts = ReusableParts(view_box=Rect(0, 0, 10, 10))
+
+    parts.add(SVG.parse(locate_test_file("square_vbox_narrow.svg")))
+    parts.add(SVG.parse(locate_test_file("square_vbox_square.svg")))
+    parts.add(SVG.parse(locate_test_file("square_vbox_narrow.svg")))
+
+    # Every square should have normalized the same
+    assert len(parts.shape_sets) == 1, parts.to_json()
+
+    paths = only(parts.shape_sets.values())
+
+    paths = [_start_at_origin(SVGPath(d=p)).relative(inplace=True) for p in paths]
+    assert {p.d for p in paths} == {
+        "M0,0 l3,0 l0,3 l-3,0 l0,-3 z"
+    }, "The square should remain 3x3; converted to relative and starting at 0,0 they should be identical"