def process_cubic(self, offset_path, blade_path, params, quality):
""" Add offset correction to a cubic bezier.
"""
r = self.config.offset
p0 = blade_path.currentPosition()
p1, p2, p3 = params
self.add_continuity_correction(offset_path, blade_path, p1)
curve = QPainterPath()
curve.moveTo(p0)
curve.cubicTo(*params)
p = QPainterPath()
p.moveTo(p0)
if quality == 1:
polygon = curve.toSubpathPolygons(IDENITY_MATRIX)[0]
else:
m = QTransform.fromScale(quality, quality)
m_inv = QTransform.fromScale(1/quality, 1/quality)
polygon = m_inv.map(curve.toSubpathPolygons(m)[0])
for point in polygon:
p.lineTo(point)
t = curve.percentAtLength(p.length())
angle = curve.angleAtPercent(t)
a = radians(angle)
dx, dy = r*cos(a), -r*sin(a)
offset_path.lineTo(point.x()+dx, point.y()+dy)
blade_path.cubicTo(*params)
def add_continuity_correction(self, offset_path, blade_path, point):
""" Adds if the upcoming angle and previous angle are not the same
we need to correct for that difference by "arcing back" about the
current blade point with a radius equal to the offset.
"""
# Current blade position
cur = blade_path.currentPosition()
# Determine direction of next move
sp = QPainterPath()
sp.moveTo(cur)
sp.lineTo(point)
next_angle = sp.angleAtPercent(1)
# Direction of last move
angle = blade_path.angleAtPercent(1)
# If not continuous it needs corrected with an arc
if isnan(angle) or isnan(next_angle):
return
if abs(angle - next_angle) > self.config.cutoff:
r = self.config.offset
a = radians(next_angle)
dx, dy = r*cos(a), -r*sin(a)
po = QPointF(cur.x()+dx, cur.y()+dy)
c = offset_path.currentPosition()
dx, dy = po.x()-cur.x()+c.x()-cur.x(), po.y()-cur.y()+c.y()-cur.y()
c1 = QPointF(cur.x()+dx, cur.y()+dy)
offset_path.quadTo(c1, po)
