Glyphs smart components by cmyr · Pull Request #1689 · googlefonts/fontc

cmyr · 2025-10-09T19:20:43Z

This is a checkpoint, and only glyphs3 sources are supported. (I believe that smart components might also exist in glyphs2 sources)

fontdrasil/src/coords.rs

rsheeter · 2025-10-09T21:31:28Z

fontdrasil/src/coords.rs

+
    pub fn has_non_zero(&self, tag: Tag) -> bool {
        self.get(tag).unwrap_or_default().to_f64() != 0.0
    }


New behavior seems testable but no new tests

fontdrasil/src/variations.rs

glyphs-reader/src/error.rs

glyphs-reader/src/font.rs

rsheeter · 2025-10-09T21:39:36Z

glyphs-reader/src/font.rs

+                    "expected only 1 or 2 in partSelection, found '{other}'"
+                ))),
+            })
+            .collect::<Result<_, _>>()?;


Is it valid to have 2 entries that both have the same SmartComponentValue, e.g. 2 Min's?

a given layer could be at the min of two different axes, if that's what you mean?

glyphs-reader/src/font.rs

rsheeter · 2025-10-09T21:48:20Z

glyphs-reader/src/font.rs

+                        _ => layer.shapes.push(shape),
+                    };
+                }
+            }


This feels more gross than it perhaps has to be?

glyphs-reader/src/font.rs

rsheeter · 2025-10-09T22:22:05Z

glyphs-reader/src/font.rs

+            Some(335)
+        );
+    }
 }


Should we test some defective smart components?

I've ported the tests from fonttools, although that doesn't provide a ton of coverage of malformed inputs. It doesn't seem like this stuff is really used much in the wild after all, so I'm inclined to just get this in as a checkpoint, and if we run into problems we can flesh it out more.

rsheeter · 2025-10-09T22:26:16Z

glyphs-reader/src/smart_components.rs

+                *range.start()
+            } else {
+                *range.end()
+            };


Is the assumption that there are exactly two and they must be min and max? We don't seem to actually check this?

rsheeter · 2025-10-09T22:30:19Z

glyphs-reader/src/smart_components.rs

The python refs are much appreciated but ... this is fairly hard to follow. Lots of noise for iters and maps and such that make it hard to see the logic. Maybe moving some of that into helper methods and/or adding comments might help?

rsheeter · 2025-10-09T22:30:57Z

glyphs-reader/src/smart_components.rs

+        .collect()
+}
+
+//https://github.com/fonttools/fonttools/blob/03a3c8ed9e/Lib/fontTools/varLib/models.py#L47


The citation makes me wonder if this belongs somewhere in the var model code?

rsheeter

LGTM subject to addressing comments where feasible

This is a checkpoint of an initial basic implementation, based on glyphsLib.

- clarify some names and docs - start porting fonttools test cases