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| """Convert SVG Path's elliptical arcs to Bezier curves. | |
| The code is mostly adapted from Blink's SVGPathNormalizer::DecomposeArcToCubic | |
| https://github.com/chromium/chromium/blob/93831f2/third_party/ | |
| blink/renderer/core/svg/svg_path_parser.cc#L169-L278 | |
| """ | |
| from fontTools.misc.transform import Identity, Scale | |
| from math import atan2, ceil, cos, fabs, isfinite, pi, radians, sin, sqrt, tan | |
| TWO_PI = 2 * pi | |
| PI_OVER_TWO = 0.5 * pi | |
| def _map_point(matrix, pt): | |
| # apply Transform matrix to a point represented as a complex number | |
| r = matrix.transformPoint((pt.real, pt.imag)) | |
| return r[0] + r[1] * 1j | |
| class EllipticalArc(object): | |
| def __init__(self, current_point, rx, ry, rotation, large, sweep, target_point): | |
| self.current_point = current_point | |
| self.rx = rx | |
| self.ry = ry | |
| self.rotation = rotation | |
| self.large = large | |
| self.sweep = sweep | |
| self.target_point = target_point | |
| # SVG arc's rotation angle is expressed in degrees, whereas Transform.rotate | |
| # uses radians | |
| self.angle = radians(rotation) | |
| # these derived attributes are computed by the _parametrize method | |
| self.center_point = self.theta1 = self.theta2 = self.theta_arc = None | |
| def _parametrize(self): | |
| # convert from endopoint to center parametrization: | |
| # https://www.w3.org/TR/SVG/implnote.html#ArcConversionEndpointToCenter | |
| # If rx = 0 or ry = 0 then this arc is treated as a straight line segment (a | |
| # "lineto") joining the endpoints. | |
| # http://www.w3.org/TR/SVG/implnote.html#ArcOutOfRangeParameters | |
| rx = fabs(self.rx) | |
| ry = fabs(self.ry) | |
| if not (rx and ry): | |
| return False | |
| # If the current point and target point for the arc are identical, it should | |
| # be treated as a zero length path. This ensures continuity in animations. | |
| if self.target_point == self.current_point: | |
| return False | |
| mid_point_distance = (self.current_point - self.target_point) * 0.5 | |
| point_transform = Identity.rotate(-self.angle) | |
| transformed_mid_point = _map_point(point_transform, mid_point_distance) | |
| square_rx = rx * rx | |
| square_ry = ry * ry | |
| square_x = transformed_mid_point.real * transformed_mid_point.real | |
| square_y = transformed_mid_point.imag * transformed_mid_point.imag | |
| # Check if the radii are big enough to draw the arc, scale radii if not. | |
| # http://www.w3.org/TR/SVG/implnote.html#ArcCorrectionOutOfRangeRadii | |
| radii_scale = square_x / square_rx + square_y / square_ry | |
| if radii_scale > 1: | |
| rx *= sqrt(radii_scale) | |
| ry *= sqrt(radii_scale) | |
| self.rx, self.ry = rx, ry | |
| point_transform = Scale(1 / rx, 1 / ry).rotate(-self.angle) | |
| point1 = _map_point(point_transform, self.current_point) | |
| point2 = _map_point(point_transform, self.target_point) | |
| delta = point2 - point1 | |
| d = delta.real * delta.real + delta.imag * delta.imag | |
| scale_factor_squared = max(1 / d - 0.25, 0.0) | |
| scale_factor = sqrt(scale_factor_squared) | |
| if self.sweep == self.large: | |
| scale_factor = -scale_factor | |
| delta *= scale_factor | |
| center_point = (point1 + point2) * 0.5 | |
| center_point += complex(-delta.imag, delta.real) | |
| point1 -= center_point | |
| point2 -= center_point | |
| theta1 = atan2(point1.imag, point1.real) | |
| theta2 = atan2(point2.imag, point2.real) | |
| theta_arc = theta2 - theta1 | |
| if theta_arc < 0 and self.sweep: | |
| theta_arc += TWO_PI | |
| elif theta_arc > 0 and not self.sweep: | |
| theta_arc -= TWO_PI | |
| self.theta1 = theta1 | |
| self.theta2 = theta1 + theta_arc | |
| self.theta_arc = theta_arc | |
| self.center_point = center_point | |
| return True | |
| def _decompose_to_cubic_curves(self): | |
| if self.center_point is None and not self._parametrize(): | |
| return | |
| point_transform = Identity.rotate(self.angle).scale(self.rx, self.ry) | |
| # Some results of atan2 on some platform implementations are not exact | |
| # enough. So that we get more cubic curves than expected here. Adding 0.001f | |
| # reduces the count of sgements to the correct count. | |
| num_segments = int(ceil(fabs(self.theta_arc / (PI_OVER_TWO + 0.001)))) | |
| for i in range(num_segments): | |
| start_theta = self.theta1 + i * self.theta_arc / num_segments | |
| end_theta = self.theta1 + (i + 1) * self.theta_arc / num_segments | |
| t = (4 / 3) * tan(0.25 * (end_theta - start_theta)) | |
| if not isfinite(t): | |
| return | |
| sin_start_theta = sin(start_theta) | |
| cos_start_theta = cos(start_theta) | |
| sin_end_theta = sin(end_theta) | |
| cos_end_theta = cos(end_theta) | |
| point1 = complex( | |
| cos_start_theta - t * sin_start_theta, | |
| sin_start_theta + t * cos_start_theta, | |
| ) | |
| point1 += self.center_point | |
| target_point = complex(cos_end_theta, sin_end_theta) | |
| target_point += self.center_point | |
| point2 = target_point | |
| point2 += complex(t * sin_end_theta, -t * cos_end_theta) | |
| point1 = _map_point(point_transform, point1) | |
| point2 = _map_point(point_transform, point2) | |
| target_point = _map_point(point_transform, target_point) | |
| yield point1, point2, target_point | |
| def draw(self, pen): | |
| for point1, point2, target_point in self._decompose_to_cubic_curves(): | |
| pen.curveTo( | |
| (point1.real, point1.imag), | |
| (point2.real, point2.imag), | |
| (target_point.real, target_point.imag), | |
| ) | |