bulge.py

"""
Move bulge by dragging the mouse. Scale with multitouch.
"""
from kivy.app import App
from kivy.core.window import Window
from kivy.uix.effectwidget import AdvancedEffectBase
from kivy.lang import Builder

EFFECT = AdvancedEffectBase()
EFFECT.glsl = """
uniform vec2 position;
uniform float radius;
uniform float angle;

vec4 effect(vec4 color, sampler2D texture, vec2 tex_coords, vec2 coords){
   vec2 relative_position = position - tex_coords;
   vec2 smoosh = -radius * log(length(relative_position)) * normalize(relative_position) / 3.0;
   return texture2D(texture, tex_coords + smoosh);}
"""
EFFECT.uniforms = {'position': (.5, .5), 'radius': .07,}

KV = """
#:import EFFECT __main__.EFFECT
EffectWidget:
    effects: EFFECT,
    Image:
        source: 'python_discord_logo.png'
"""

class Bulge(App):
    def build(self):
        self._touches = []
        Window.bind(on_touch_up=self._on_touch_up,
                    on_touch_down=self._on_touch_down,
                    on_touch_move=self._on_touch_move)
        return Builder.load_string(KV)

    def transform_on_touch(self, touch):
        ax, ay = self._touches[-2].pos

        cx = (touch.x - ax) / Window.width
        cy = (touch.y - ay) / Window.height
        current_length = (cx**2 + cy**2)**.5

        px = (touch.px - ax) / Window.width
        py = (touch.py - ay) / Window.height
        previous_length = (px**2 + py**2)**.5

        EFFECT.uniforms['radius'] += current_length - previous_length

    def _on_touch_up(self, _, touch):
        self._touches.remove(touch)

    def _on_touch_down(self, _, touch):
        if touch.button == 'left' and not self._touches:
            EFFECT.uniforms['position'] = touch.spos
        self._touches.append(touch)

    def _on_touch_move(self, _, touch):
        if touch.button == 'left':
            if len(self._touches) == 1:
                EFFECT.uniforms['position'] = touch.spos
            else:
                self.transform_on_touch(touch)

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