def _apply_gradient_common_parts(
gradient: etree.Element,
paint: _GradientPaint,
transform: Affine2D = Affine2D.identity(),
):
gradient.attrib["gradientUnits"] = "userSpaceOnUse"
for stop in paint.stops:
stop_el = etree.SubElement(gradient, "stop")
stop_el.attrib["offset"] = _ntos(stop.stopOffset)
stop_el.attrib["stop-color"] = stop.color.opaque().to_string()
if stop.color.alpha != 1.0:
stop_el.attrib["stop-opacity"] = _ntos(stop.color.alpha)
if paint.extend != Extend.PAD:
gradient.attrib["spreadMethod"] = paint.extend.name.lower()
transform = transform.round(_DEFAULT_ROUND_NDIGITS)
if transform != Affine2D.identity():
# Safari has a bug which makes it reject a gradient if gradientTransform
# contains an 'involutory matrix' (i.e. matrix whose inverse equals itself,
# such that M @ M == Identity, e.g. reflection), hence the following hack:
# https://github.com/googlefonts/nanoemoji/issues/268
# https://en.wikipedia.org/wiki/Involutory_matrix
# TODO: Remove once the bug gets fixed
if transform @ transform == Affine2D.identity():
transform = transform._replace(a=transform.a + 0.00001)
assert transform.inverse() != transform
gradient.attrib["gradientTransform"] = transform.tostring()
def _svg_matrix(transform: Affine2D) -> str:
return transform.round(_DEFAULT_ROUND_NDIGITS).tostring()