Flattening components does not handle transformed components well

[khaledhosny]

In Test.glyphs I have many rotated, translated, or flipped components, but flattening components seems to not handle all of them correctly.

In the Test-Regular.ttf (built with fontmake -f), many components are mis positioned.

Below bad font (built with -f fontmake option) and above the good font (built without the option):

[khaledhosny]

(These are activated with numr feature).

[moyogo]

The issue is :

ufo2ft/Lib/ufo2ft/filters/flattenComponents.py

Line 47 in 3ad75bf

tr = tr.transform(component.transformation)

Applying scale transforms to translation transforms breaks the translations.

We should do something along those lines:

@@ -44,7 +44,9 @@ def _flattenComponent(glyphSet, component):
     for nested in glyph.components:
         flattened_components = _flattenComponent(glyphSet, nested)
         for i, (_, tr) in enumerate(flattened_components):
-            tr = tr.transform(component.transformation)
-            flattened_components[i] = (flattened_components[i][0], tr)
+            flat_tr = Transform()
+            flat_tr = flat_tr.translate(*component.transformation[4:]).translate(*tr[4:])
+            flat_tr = flat_tr.transform(Transform(*component.transformation[:4])).transform(Transform(*tr[:4]))
+            flattened_components[i] = (flattened_components[i][0], flat_tr)
         all_flattened_components.extend(flattened_components)
     return all_flattened_components

[khaledhosny]

This seems to work for me:

diff --git a/Lib/ufo2ft/filters/flattenComponents.py b/Lib/ufo2ft/filters/flattenComponents.py
index aa234b6..72ebdc0 100644
--- a/Lib/ufo2ft/filters/flattenComponents.py
+++ b/Lib/ufo2ft/filters/flattenComponents.py
@@ -43,8 +43,10 @@ def _flattenComponent(glyphSet, component):
     all_flattened_components = []
     for nested in glyph.components:
         flattened_components = _flattenComponent(glyphSet, nested)
-        for i, (_, tr) in enumerate(flattened_components):
-            tr = tr.transform(component.transformation)
-            flattened_components[i] = (flattened_components[i][0], tr)
+        for i, (name, tr) in enumerate(flattened_components):
+            flat_tr = Transform(*component.transformation)
+            flat_tr = flat_tr.translate(tr.dx, tr.dy)
+            flat_tr = flat_tr.transform((tr.xx, tr.xy, tr.yx, tr.yy, 0, 0))
+            flattened_components[i] = (name, flat_tr)
         all_flattened_components.extend(flattened_components)
     return all_flattened_components

[arrowtype]

Not sure it’s useful to say, but I’ve run into problems here, as well.

I can’t easily offer a simple reproduction case, but this the result of using decomposeTransformedComponents and flattenComponents at https://github.com/arrowtype/recursive/tree/b61385b2e6d40e4684fcc042957ec468863a4e94.

Related issues:

• Check for nested components fonttools/fontbakery#2961 (a FontBakery check for flattened components)
• Printing issues due to running TTF fonts through a PostScript 3 printer arrowtype/recursive#412 (printing issues triggered by nested components)