blit_fog.py

from array import array

from kivy.app import App
from kivy.lang import Builder
from kivy.graphics.fbo import Fbo
from kivy.graphics.texture import Texture
from kivy.uix.widget import Widget
from kivy.properties import ListProperty, ObjectProperty

KV = '''
#:import F kivy.factory.Factory
#:import random random.random

FloatLayout:
    GridLayout:
        cols: 20
        on_parent:
            for i in range(20 * 20): self.add_widget(F.ColorLabel(text=str(i)))
    Fog:
        texture_size: 100, 100
        pencil_size: 5, 5

<ColorLabel@Label>:
    canvas.before:
        Color:
            rgba: [random() for i in range(4)]
        Rectangle:
            pos: self.pos
            size: self.size

<Fog>:
    canvas:
        Rectangle:
            size: self.size
            pos: self.pos
            texture: self.texture

'''

class Fog(Widget):
    texture_size = ListProperty([0, 0])
    texture = ObjectProperty(allownone=True)
    pencil_size = ListProperty([1, 1])

    def on_texture_size(self, *args):
        self.texture = texture = Texture.create(size=self.texture_size)

        size = self.texture_size[0] * self.texture_size[1]
        buf = sum(([0, 0, 0, 255] for x in range(size)), [])
        arr = array('B', buf)
        texture.blit_buffer(arr, colorfmt='rgba', bufferfmt='ubyte')

    def on_touch_move(self, touch):
        width, height = self.texture_size
        x = (touch.x - self.x) / self.width
        y = (touch.y - self.y) / self.height

        if not (0 < x < 1 and 0 < y < 1):
            return

        texture = self.texture

        ps = self.pencil_size

        texture.blit_buffer(
            array('B', [0, 0, 0, 0] * ps[0] * ps[1]),
            colorfmt='rgba',
            bufferfmt='ubyte',
            size=ps,
            pos=(x * width - ps[0] / 2, y * height - ps[1] / 2)
        )
        self.canvas.flag_update()


class DrawApp(App):
    def build(self):
        return Builder.load_string(KV)


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

test_fbo_blit.py

from array import array

from kivy.app import App
from kivy.lang import Builder
from kivy.graphics.fbo import Fbo
from kivy.graphics.texture import Texture
from kivy.uix.widget import Widget
from kivy.properties import ListProperty, ObjectProperty

KV = '''
#:import F kivy.factory.Factory
#:import random random.random

FloatLayout:
    GridLayout:
        cols: 20
        on_parent:
            for i in range(20 * 20): self.add_widget(F.ColorLabel(text=str(i)))
    Fog:
        texture_size: 100, 100
        pencil_size: 5, 5

<ColorLabel@Label>:
    canvas.before:
        Color:
            rgba: [random() for i in range(4)]
        Rectangle:
            pos: self.pos
            size: self.size

<Fog>:
    canvas:
        Rectangle:
            size: self.size
            pos: self.pos
            texture: self.texture

'''

class Fog(Widget):
    texture_size = ListProperty([0, 0])
    texture = ObjectProperty(allownone=True)
    pencil_size = ListProperty([1, 1])

    def on_texture_size(self, *args):
        self.texture = texture = Texture.create(size=self.texture_size)

        size = self.texture_size[0] * self.texture_size[1]
        buf = sum(([0, 0, 0, 255] for x in range(size)), [])
        arr = array('B', buf)
        texture.blit_buffer(arr, colorfmt='rgba', bufferfmt='ubyte')

    def on_touch_move(self, touch):
        width, height = self.texture_size
        x = (touch.x - self.x) / self.width
        y = (touch.y - self.y) / self.height

        if not (0 < x < 1 and 0 < y < 1):
            return

        texture = self.texture

        ps = self.pencil_size

        texture.blit_buffer(
            array('B', [0, 0, 0, 0] * ps[0] * ps[1]),
            colorfmt='rgba',
            bufferfmt='ubyte',
            size=ps,
            pos=(x * width - ps[0] / 2, y * height - ps[1] / 2)
        )
        self.canvas.flag_update()


class DrawApp(App):
    def build(self):
        return Builder.load_string(KV)


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

cool