gistfile1.py

from kivy.app import App
from kivy.core.window import Window
from kivy.lang import Builder
from kivy.uix.widget import Widget
from kivy.graphics.texture import Texture
from kivy.graphics import RenderContext
from itertools import chain

shader_distort_samples = '''
$HEADER$

uniform sampler2D texture1;

void main() {
    vec4 val = texture2D(texture1, vec2(tex_coord0.y, 0));
    gl_FragColor = texture2D(texture0, vec2(tex_coord0.x, val.x));
}

'''

Builder.load_string('''
#:import Logger kivy.logger.Logger

<MultitextureWidget>:
    canvas:
        Color:
            rgba: 1, 1, 1, 1
        BindTexture:
            texture: self.samples_texture
            index: 1
        Rectangle:
            size: self.size
            pos: self.pos
            source: 'test.png'
''')


class MultitextureWidget(Widget):
    samples_texture = ObjectProperty(None)

    def __init__(self, **kwargs):
        self.canvas = RenderContext()
        self.canvas.shader.fs = shader_distort_samples
        self.samples_texture = Texture.create(size=(256, 1), colorfmt='RGB')

        import math
        samples = list((int(math.floor(math.sin((math.pi/2) * (i / 255.)) * 255.)), 0, 0) for i in range(255))
        buf = ''.join(map(chr, chain(*samples)))
        self.samples_texture.blit_buffer(buf, colorfmt='rgb', bufferfmt='ubyte')

        self.setup_canvas()

        # set the texture1 to use texture index 1
        self.canvas['texture1'] = 1

        # call the constructor of parent
        # if they are any graphics object, they will be added on our new canvas
        super(MultitextureWidget, self).__init__(**kwargs)

        # self.update_glsl()

    def on_size(self, i, v):
        self.setup_canvas()
        self.update_glsl()

    def on_pos(self, i, v):
        self.setup_canvas()
        self.update_glsl()

    def update_glsl(self, *largs):
        # This is needed for the default vertex shader.
        self.canvas['projection_mat'] = Window.render_context['projection_mat']
        self.canvas['modelview_mat'] = Window.render_context['modelview_mat']


class StretchedImageApp(App):
    def build(self):
        return MultitextureWidget()