Add elafronBounds

docs/font-metadata.md

@@ -4,6 +4,40 @@ Each font can optionally provide a metadata file containing information that can
 
 All positions and widths are specified in ems.
 
+## metrics
+
+This section contains font-wide measurements and adjustments. The
+`elafronBounds` object gives the horizontal outline bounds of the elafron
+component in composite glyphs.
+
+```js
+{
+  "metrics": {
+    "ascent": 0.8,
+    "descent": 0.2,
+    "winAscent": 1.4,
+    "winDescent": 0.466,
+    "oligonMidpoint": 0.307,
+    "elafronBounds": {
+      "runningElafron": {
+        "left": 0.59,
+        "right": 1.696
+      },
+      "petastiRunningElafron": {
+        "left": 0.425,
+        "right": 1.431
+      }
+    }
+  },
+  ...
+}
+```
+
+These bounds can be used to terminate a melisma at the component's edge
+without assuming that it matches the stand-alone glyph. Given the composite
+glyph's advance width, the signed offset needed to center lyrics beneath its
+elafron is `left + right - advanceWidth`.
+
 ## glyphsWithAnchors
 
 This section contains the anchor points for all glyphs that contain anchors. If mark-to-base positioning is not available, marks can be positioned using the data in this section.

fonts/neanes.metadata.json

@@ -6,7 +6,17 @@
     "descent": 0.2,
     "winAscent": 1.4,
     "winDescent": 0.466,
-    "oligonMidpoint": 0.307
+    "oligonMidpoint": 0.307,
+    "elafronBounds": {
+      "runningElafron": {
+        "left": 0.59,
+        "right": 1.696
+      },
+      "petastiRunningElafron": {
+        "left": 0.425,
+        "right": 1.431
+      }
+    }
   },
   "glyphsWithAnchors": {
     "ison": {

fonts/neanesengraving.metadata.json

@@ -6,7 +6,17 @@
     "descent": 0.2,
     "winAscent": 1.4,
     "winDescent": 0.466,
-    "oligonMidpoint": 0.307
+    "oligonMidpoint": 0.307,
+    "elafronBounds": {
+      "runningElafron": {
+        "left": 0.542,
+        "right": 1.648
+      },
+      "petastiRunningElafron": {
+        "left": 0.502,
+        "right": 1.508
+      }
+    }
   },
   "glyphsWithAnchors": {
     "ison": {

fonts/neanesrtl.metadata.json

@@ -6,7 +6,17 @@
     "descent": 0.2,
     "winAscent": 1.4,
     "winDescent": 0.466,
-    "oligonMidpoint": 0.307
+    "oligonMidpoint": 0.307,
+    "elafronBounds": {
+      "runningElafron": {
+        "left": 0.08,
+        "right": 1.185
+      },
+      "petastiRunningElafron": {
+        "left": 0.085,
+        "right": 1.091
+      }
+    }
   },
   "glyphsWithAnchors": {
     "ison": {

fonts/neanesrtlengraving.metadata.json

@@ -6,7 +6,17 @@
     "descent": 0.2,
     "winAscent": 1.4,
     "winDescent": 0.466,
-    "oligonMidpoint": 0.307
+    "oligonMidpoint": 0.307,
+    "elafronBounds": {
+      "runningElafron": {
+        "left": -0.002,
+        "right": 1.104
+      },
+      "petastiRunningElafron": {
+        "left": 0.019,
+        "right": 1.024
+      }
+    }
   },
   "glyphsWithAnchors": {
     "ison": {

fonts/neanesstathisseries.metadata.json

@@ -6,7 +6,17 @@
     "descent": 0.2,
     "winAscent": 1.4,
     "winDescent": 0.466,
-    "oligonMidpoint": 0.309
+    "oligonMidpoint": 0.309,
+    "elafronBounds": {
+      "runningElafron": {
+        "left": 0.72,
+        "right": 1.772
+      },
+      "petastiRunningElafron": {
+        "left": 0.389,
+        "right": 1.515
+      }
+    }
   },
   "glyphsWithAnchors": {
     "ison": {

fonts/neanesstathisseriesengraving.metadata.json

@@ -6,7 +6,17 @@
     "descent": 0.2,
     "winAscent": 1.4,
     "winDescent": 0.466,
-    "oligonMidpoint": 0.309
+    "oligonMidpoint": 0.309,
+    "elafronBounds": {
+      "runningElafron": {
+        "left": 0.72,
+        "right": 1.772
+      },
+      "petastiRunningElafron": {
+        "left": 0.721,
+        "right": 1.847
+      }
+    }
   },
   "glyphsWithAnchors": {
     "ison": {

scripts/generate-font-metadata.py

@@ -88,6 +88,24 @@ def contour_bbox(contour):
     return xmin, ymin, xmax, ymax
 
 
+def find_widest_contour_bbox(glyph):
+    bboxes = [bbox for contour in glyph.foreground if (bbox := contour_bbox(contour))]
+
+    if not bboxes:
+        return None
+
+    return max(bboxes, key=lambda bbox: bbox[2] - bbox[0])
+
+
+def find_lowest_contour_bbox(glyph):
+    bboxes = [bbox for contour in glyph.foreground if (bbox := contour_bbox(contour))]
+
+    if not bboxes:
+        return None
+
+    return min(bboxes, key=lambda bbox: bbox[1])
+
+
 def create_temp_glyph_from_contours(font, source_glyph, contours, name):
     temp_glyph = font.createChar(-1, name)
     temp_glyph.clear()
@@ -355,6 +373,7 @@ def asdict(self):
             "winAscent": round(self.font.os2_winascent / self.font.em, 3),
             "winDescent": round(self.font.os2_windescent / self.font.em, 3),
             "oligonMidpoint": round(self.font.oligon_midpoint / self.font.em, 3),
+            "elafronBounds": self.elafron_bounds(),
         }
 
         anchors = self.anchors()
@@ -396,6 +415,32 @@ def asdict(self):
 
         return d
 
+    def elafron_bounds(self):
+        # In runningElafron the wider of the two adjacent contours is the
+        # elafron. In petastiRunningElafron the elafron is the contour below
+        # the petasti. Derive the component bounds from those outlines instead
+        # of assuming they match the stand-alone elafron.
+        contour_bboxes = {
+            "runningElafron": find_widest_contour_bbox(self.font["runningElafron"]),
+            "petastiRunningElafron": find_lowest_contour_bbox(
+                self.font["petastiRunningElafron"]
+            ),
+        }
+
+        bounds = {}
+
+        for glyph_name, bbox in contour_bboxes.items():
+            if bbox is None:
+                raise ValueError(f"Cannot locate the elafron in {glyph_name}")
+
+            elafron_left, _, elafron_right, _ = bbox
+            bounds[glyph_name] = {
+                "left": round(elafron_left / self.font.em, 3),
+                "right": round(elafron_right / self.font.em, 3),
+            }
+
+        return bounds
+
     def anchors(self):
         all_anchors = {}