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Bezier Example

pic7

This example shows a closed Bezier curve computed from a polygon. You should see a purple polygon, a red bezier curve computed from the polygon, and two sliders. You can drag points on the polygon to recompute the curve. The two sliders control the dash length of the dashed lines making up the two shapes.

File canvas/bezier.py

'''
Bezier Example
==============

This example shows a closed Bezier curve computed from a polygon. You
should see a purple polygon, a red bezier curve computed from the polygon,
and two sliders. You can drag points on the polygon to recompute the curve.
The two sliders control the dash length of the dashed lines making up the two
shapes.

'''
from kivy.app import App
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.slider import Slider
from kivy.graphics import Color, Bezier, Line


class BezierTest(FloatLayout):

    def __init__(self, points=[], loop=False, *args, **kwargs):
        super(BezierTest, self).__init__(*args, **kwargs)
        self.d = 10  # pixel tolerance when clicking on a point
        self.points = points
        self.loop = loop
        self.current_point = None  # index of point being dragged

        with self.canvas:
            Color(1.0, 0.0, 0.0)

            self.bezier = Bezier(
                    points=self.points,
                    segments=150,
                    loop=self.loop,
                    dash_length=100,
                    dash_offset=10)

            Color(1.0, 0.0, 1.0)
            self.line = Line(
                    points=self.points + self.points[:2],
                    dash_offset=10,
                    dash_length=100)

        s = Slider(y=0, pos_hint={'x': .3}, size_hint=(.7, None), height=50)
        s.bind(value=self._set_bezier_dash_offset)
        self.add_widget(s)

        s = Slider(y=50, pos_hint={'x': .3}, size_hint=(.7, None), height=50)
        s.bind(value=self._set_line_dash_offset)
        self.add_widget(s)

    def _set_bezier_dash_offset(self, instance, value):
        # effect to reduce length while increase offset
        self.bezier.dash_length = 100 - value
        self.bezier.dash_offset = value

    def _set_line_dash_offset(self, instance, value):
        # effect to reduce length while increase offset
        self.line.dash_length = 100 - value
        self.line.dash_offset = value

    def on_touch_down(self, touch):
        if self.collide_point(touch.pos[0], touch.pos[1]):
            for i, p in enumerate(list(zip(self.points[::2],
                                           self.points[1::2]))):
                if (abs(touch.pos[0] - self.pos[0] - p[0]) < self.d and
                        abs(touch.pos[1] - self.pos[1] - p[1]) < self.d):
                    self.current_point = i + 1
                    return True
            return super(BezierTest, self).on_touch_down(touch)

    def on_touch_up(self, touch):
        if self.collide_point(touch.pos[0], touch.pos[1]):
            if self.current_point:
                self.current_point = None
                return True
            return super(BezierTest, self).on_touch_up(touch)

    def on_touch_move(self, touch):
        if self.collide_point(touch.pos[0], touch.pos[1]):
            c = self.current_point
            if c:
                self.points[(c - 1) * 2] = touch.pos[0] - self.pos[0]
                self.points[(c - 1) * 2 + 1] = touch.pos[1] - self.pos[1]
                self.bezier.points = self.points
                self.line.points = self.points + self.points[:2]
                return True
            return super(BezierTest, self).on_touch_move(touch)


class Main(App):

    def build(self):
        from math import cos, sin, radians
        x = y = 150
        z = 100
        # Pacman !
        points = [x, y]
        for i in range(45, 360, 45):
            i = radians(i)
            points.extend([x + cos(i) * z, y + sin(i) * z])
        return BezierTest(points=points, loop=True)


if __name__ == '__main__':
    Main().run()