animated voronoi of mona lisa

__init__.py

from random import random
from itertools import chain

from kivy.uix.effectwidget import AdvancedEffectBase
from kivy.animation import Animation
from kivy.clock import Clock
from kivy.properties import ListProperty
from kivy.core.window import Window
Window.size = 300, 400

POINTS = 512 * 4

effect_voronoi = '''
uniform float points[%s];
uniform int num_points;

float length2(vec2 xy)
{
    return pow(xy.x, 2.0) + pow(xy.y, 2.0);
}

vec4 effect(vec4 vcolor, sampler2D texture, vec2 texcoord, vec2 pixel_coords)
{
    vec2 nearest = vec2(0., 0.);
    float min_dist = 10.; // much larger than texture (1, 1)

    int i;
    vec2 point;
    float dist;
    // very costly, each pixel will go through half of the list of points on average
    for (i = 0; i < num_points; i++) {
        point = vec2(points[i * 2], points[i * 2 + 1]);
        dist = distance(point, texcoord);
        if (dist < min_dist) {
            min_dist = dist;
            nearest = point;
        } else {
            if (point.x > texcoord.x + min_dist)
                break;
        }
    }

    return texture2D(texture, nearest);
}
''' % POINTS


class VoronoiEffect(AdvancedEffectBase):
    points = ListProperty()
    glsl = effect_voronoi

    def on_points(self, *args):
        self.uniforms['num_points'] = len(self.points) // 2
        self.uniforms['points'] = [float(x) for x in self.points]


if __name__ == '__main__':
    import kivy
    from kivy.app import App
    from kivy.factory import Factory

    class Application(App):
        random_points = ListProperty()
        touches = ListProperty()

        def build(self):
            self.voronoi = voronoi = VoronoiEffect()
            effects = [voronoi]
            root = Factory.EffectWidget(effects=effects)

            self.random_points = [(random(), random()) for r in range(POINTS // 2)]
            root.bind(
                on_touch_down=self.create_point,
                on_touch_move=self.update_point,
                on_touch_up=self.remove_point,
            )

            root.add_widget(
                Factory.AsyncImage(
                    source='https://upload.wikimedia.org/wikipedia/commons/thumb/e/ec/Mona_Lisa%2C_by_Leonardo_da_Vinci%2C_from_C2RMF_retouched.jpg/300px-Mona_Lisa%2C_by_Leonardo_da_Vinci%2C_from_C2RMF_retouched.jpg'
                )
            )
            Clock.schedule_interval(self.animate_points, 3)
            self.bind(random_points=self.update_points)
            self.update_points()
            return root

        def animate_points(self, dt):
            Animation(
                random_points=[(random(), random()) for r in range(POINTS // 2)],
                d=2,
                t='out_quad',
            ).start(self)

        def update_points(self, *args):
            if not self.root:
                return

            W, H = self.root.size
            points = self.random_points + [(touch.x / W, touch.y / H) for touch in self.touches]
            points.sort()
            self.voronoi.points = tuple(chain(*points))

        def create_point(self, _, touch):
            self.touches.append(touch)
            self.update_points()

        def update_point(self, _, touch):
            self.update_points()

        def remove_point(self, _, touch):
            self.touches.remove(touch)

    Application().run()