[ttGlyphPen_test] Add bounds test for 'nested' composite glyph

This is a regression introduced with https://github.com/fonttools/fonttools/pull/3750

The test currently fails because we are now applying rounding to the
coordinates extracted from each component of a composite glyph, *before*
these are transformed; with nested components of components with non trivial transforms, the rounding errors compound leading to incorrect bounds.

Tests/pens/ttGlyphPen_test.py

@@ -614,6 +614,52 @@ class TTGlyphPointPenTest(TTGlyphPenTestBase):
         # these are the expected bounds as computed from the rounded coordinates
         self.assertGlyphBoundsEqual(compositeGlyph, (74, 680, 329, 834))
 
+    def test_composite_bounds_with_nested_components(self):
+        # The following test case is taken from Joan.glyphs at
+        # https://github.com/PaoloBiagini/Joan
+        # There's a composite glyph 'bullet.sc' which contains a transformed
+        # component 'bullet', which in turn is a composite glyph referencing
+        # another transformed components ('period'). The two transformations
+        # combine to produce the final transformed coordinates, but the necessary
+        # rounding should only happen at the end, and not at each intermediate
+        # level of the nested component tree.
+        glyphSet = {}
+        pen = TTGlyphPointPen(glyphSet)
+
+        pen.beginPath()
+        pen.addPoint((141.0, -8.0), "qcurve")
+        pen.addPoint((168.0, -8.0), None)
+        pen.addPoint((205.0, 30.5), None)
+        pen.addPoint((205.0, 56.0), "qcurve")
+        pen.addPoint((205.0, 82.25), None)
+        pen.addPoint((168.0, 118.0), None)
+        pen.addPoint((141.0, 118.0), "qcurve")
+        pen.addPoint((114.0, 118.0), None)
+        pen.addPoint((78.0, 79.5), None)
+        pen.addPoint((78.0, 54.0), "qcurve")
+        pen.addPoint((78.0, 27.75), None)
+        pen.addPoint((114.0, -8.0), None)
+        pen.endPath()
+        glyphSet["period"] = pen.glyph()
+
+        pen.addComponent("period", (1.6, 0, 0, 1.6, -41, 140))
+        glyphSet["bullet"] = pen.glyph()
+
+        pen.addComponent("bullet", (0.9, 0, 0, 0.9, 9, 49))
+        compositeGlyph = glyphSet["bullet.sc"] = pen.glyph()
+
+        # this is the xMin of 'bullet.sc' glyph if coordinates were left unrounded
+        coords, _, _ = compositeGlyph.getCoordinates(glyphSet)
+        assert pytest.approx(min(x for x, y in coords)) == 84.42033
+
+        compositeGlyph.recalcBounds(glyphSet)
+
+        # if rounding happened at intermediate stages (i.e. after extracting transformed
+        # coordinates of 'period' component from 'bullet', before transforming 'bullet'
+        # component in 'bullet.sc'), the rounding errors would compound leading to xMin
+        # incorrectly be equal to 85. Whereas 84.42033 should round down to 84.
+        self.assertGlyphBoundsEqual(compositeGlyph, (84, 163, 267, 345))
+
     def test_open_path_starting_with_move(self):
         # when a contour starts with a 'move' point, it signifies the beginnig
         # of an open contour.