gistfile1.txt

from kivy.base import runTouchApp
from kivy.properties import ListProperty
from kivy.lang import Builder
from kivy.uix.effectwidget import EffectWidget, EffectBase, AdvancedEffectBase, InvertEffect


effect_string = '''
uniform vec2 touch;

vec4 effect(vec4 color, sampler2D texture, vec2 tex_coords, vec2 coords)
{
    vec2 distance = coords - touch;
    float dist_mag = 10.0 * dot(distance, distance);
    vec3 multiplier = vec3(abs(sin(dist_mag + time)));
    return vec4(multiplier * color.xyz, color.w);
}
'''

class TouchEffect(AdvancedEffectBase):
    touch = ListProperty([0.0, 0.0])

    def __init__(self, *args, **kwargs):
        super(TouchEffect, self).__init__(*args, **kwargs)
        self.glsl = effect_string

        self.uniforms = {'touch': [0.0, 0.0]}

    def on_touch(self, *args, **kwargs):
        self.uniforms['touch'] = [float(i) for i in self.touch]


class TouchWidget(EffectWidget):
    def __init__(self, *args, **kwargs):
        super(TouchWidget, self).__init__(*args, **kwargs)
        self.effect = TouchEffect()
        self.effects = [self.effect]

    def on_touch_down(self, touch):
        super(TouchWidget, self).on_touch_down(touch)
        self.on_touch_move(touch)

    def on_touch_move(self, touch):
        self.effect.touch = touch.pos

    
root = Builder.load_string('''
TouchWidget:
    Button:
        text: 'Some text!'
    Image:
        source: 'data/logo/kivy-icon-512.png'
        allow_stretch: True
        keep_ratio: False
''')

runTouchApp(root)