a RF script to preview a glyphs "convex hull" and "centroid"...

CentroidHull.py

from mojo.roboFont import RGlyph
from fontTools.pens.basePen import BasePen
from mojo.subscriber import Subscriber, registerGlyphEditorSubscriber, unregisterGlyphEditorSubscriber, listRegisteredSubscribers
from fontPens.flattenPen import flattenGlyph
from scipy.spatial import ConvexHull

class MyCopyDecomposingPen(BasePen):
    def __init__(self, glyphSet, outPen):
        super(MyCopyDecomposingPen, self).__init__(glyphSet)
        self._moveTo = outPen.moveTo
        self._lineTo = outPen.lineTo
        self._curveToOne = outPen.curveTo
        self._closePath = outPen.closePath
        self._endPath = outPen.endPath


class CentroidPreview(Subscriber):
    debug = False

    def build(self):
        glyphEditor = self.getGlyphEditor()
        self.container = glyphEditor.extensionContainer(
            identifier='com.roboFont.CentroidPreview.background',
            location='background',
            clear=True,
        )
        self.convexHullLayer = self.container.appendPathSublayer(
            strokeColor=(1,0,0,1),
            fillColor=(1,0,0,.05),
            strokeWidth=1,
            )
        self.centroidLayer = self.container.appendSymbolSublayer(
            position=(0,0)
        )

    def destroy(self):
        self.container.clearSublayers()

    def glyphEditorDidSetGlyph(self, info):
        glyph = info['glyph']
        if glyph is not None:
            self.drawCentroid(glyph)

    def glyphEditorGlyphDidChange(self, info):
        glyph = info['glyph']
        if glyph is not None:
            self.drawCentroid(glyph)
        
    def glyphEditorDidMouseDrag(self, info):
        glyph = info['glyph']
        if glyph is not None:
            self.drawCentroid(glyph)


    def centroid(self,vertices):
        # https://stackoverflow.com/questions/75699024/finding-the-centroid-of-a-polygon-in-python
        x, y = 0, 0
        n = len(vertices)
        signed_area = 0
        for i in range(len(vertices)):
            x0, y0 = vertices[i]
            x1, y1 = vertices[(i + 1) % n]
            # shoelace formula
            area = (x0 * y1) - (x1 * y0)
            signed_area += area
            x += (x0 + x1) * area
            y += (y0 + y1) * area
        signed_area *= 0.5
        x /= 6 * signed_area
        y /= 6 * signed_area
        return x, y
    
    def drawCentroid(self, glyph):
        if glyph.isEmpty():
            self.convexHullLayer.setVisible(False)
            self.centroidLayer.setVisible(False)
        else:
            
            self.convexHullLayer.setVisible(True)
            self.centroidLayer.setVisible(True)
            
            tempGlyph = RGlyph()
            tempGlyph.appendGlyph(glyph)
            pen = MyCopyDecomposingPen(glyph.font, tempGlyph.getPen())
            tempGlyph.draw(pen)
            tempGlyph.removeOverlap()
            flattenGlyph(tempGlyph,10)
        
            points = [(point.x,point.y) for contour in tempGlyph.contours for point in contour.points]
            if points:
                hull = ConvexHull(points)
                hullPoints = hull.points[hull.vertices]
    
                pen = self.convexHullLayer.getPen()
                pen.moveTo(hullPoints[0])
                for hp in hullPoints[1:]:
                    pen.lineTo(hp)
                pen.closePath()

                x, y = self.centroid([tuple(p) for p in hullPoints])

                cgPath = pen.path        
                self.convexHullLayer.setPath(cgPath)
            
                self.centroidLayer.setImageSettings(
                    dict(
                        name="star",
                        size=(10,10),
                        fillColor=(1, 0, 0, 1),
                        pointCount=10
                    )
                )
                self.centroidLayer.setPosition((x,y))
            
            
            
if __name__ == '__main__':
    finder = [subs for subs in listRegisteredSubscribers() if 'CentroidPreview' in subs.getIdentifier()]
    if finder:        
        for s in finder:
            unregisterGlyphEditorSubscriber(s)
    else:
        registerGlyphEditorSubscriber(CentroidPreview)