Robofont: skew selected segments to Italic angle

skew_selected_segments_to_italic_angle.py

import math


def calc_vector(p1, p2):
    x1, y1 = p1
    x2, y2 = p2
    return x2 - x1, y2 - y1


def calc_distance(p1, p2):
    return math.hypot(*calc_vector(p1, p2))


def calc_angle(p1, p2):
    dx, dy = calc_vector(p1, p2)
    return math.atan2(dy, dx)


def polar_point(center, radius, angle):
    '''
    Get points on a circle for arbitrary angle
    '''
    x = center[0] + radius * math.cos(angle)
    y = center[1] + radius * math.sin(angle)
    return x, y


g = CurrentGlyph()
italic_angle = (math.pi / 2) + math.radians(g.font.info.italicAngle)
sel_segments = [s for c in g.contours for s in c.segments if s.selected]

g.prepareUndo('skew segments')
for segment in sel_segments:

    point = segment.points[-1]
    contour = segment.contour
    prev_segment = contour[segment.index - 1 % len(contour.segments)]
    prev_point = prev_segment.points[-1]

    point_a, point_b = prev_point.position, point.position

    segment_angle = calc_angle(point_a, point_b)
    segment_length = calc_distance(point_a, point_b)
    segment_center = polar_point(point_a, segment_length / 2, segment_angle)
    target_angle = italic_angle

    if segment_angle < 0:
        segment_angle += math.pi
    skew = math.degrees(segment_angle) - math.degrees(target_angle)
    prev_point.skewBy((skew, 0), segment_center)
    point.skewBy((skew, 0), segment_center)
    prev_point.round()
    point.round()

g.changed()
g.performUndo()