kivy 剪切文本变形

Question

as the canvas instructions Stencil and Scissor (which seem to mo me have the same effect) are used to create masks and draw on top of it, im wondering have one could achieve this effect:

Drawing any shape on top of a background image (so far so easy). Then cut text out of the shape in order to look through on the background.

Is there any solution for that? Or any kivy/openGL instructions i have missed?

Answer 1

Here is something that comes close to what you want. It is a brute force method that makes the text of a kivy.core.text.Label transparent and then uses that texture in a canvas Rectangle:

from kivy.app import App
from kivy.clock import Clock
from kivy.graphics.context_instructions import Color
from kivy.graphics.texture import Texture
from kivy.graphics.vertex_instructions import Rectangle
from kivy.lang import Builder
from kivy.uix.floatlayout import FloatLayout
from kivy.core.text import Label as CoreLabel

class MyWidget(FloatLayout):
    pass

Builder.load_string('''
<MyWidget>:
    Image:
        source: 'tester.png'
        allow_stretch: True
        keep_ratio: True
''')


class TestApp(App):
    def build(self):
        Clock.schedule_once(self.doit)
        return MyWidget()

    def doit(self, dt):
        # build a Rectangle half the size and centered on the root (MyWidget)
        size = (self.root.width/2, self.root.height/2)
        pos = (self.root.x + (self.root.width - size[0])/2, self.root.y + (self.root.height - size[1])/2)
        with self.root.canvas.after:
            Color(1,1,1,1)
            self.rect = Rectangle(pos=pos, size=size)

        # create a Texture with desired text and desired size
        label = CoreLabel(text='Hello', font_name='Roboto-Bold', font_size=300, valign='center', halign='center',
                          size=self.root.size, color=(1,1,1,1))
        label.refresh()

        # make the actual text transparent, and assign the new Texture to the Rectangle
        self.rect.texture =  self.make_text_transparent(label.texture, (255, 0, 0, 255))

    def make_text_transparent(self, texture, bg_color):
        # bg_color is a 4 tuple of byte values in the range 0-255
        # The normal Label texture is transparent except for the text itself
        # This code changes the texture to make the text transparent, and everything else
        # gets set to bg_color
        pixels = list(texture.pixels)
        for index in range(3, len(pixels)-4, 4):
            if pixels[index] == 0:
                # change transparent pixels to the bg_color
                pixels[index-3:index+1] = bg_color
            else:
                # make the text itself transparent
                pixels[index] = 0

        # create a new texture, blit the new pixels, and return the new texture
        new_texture = Texture.create(size=texture.size, colorfmt='rgba')
        new_texture.blit_buffer(bytes(pixels), colorfmt='rgba', bufferfmt='ubyte')
        new_texture.flip_vertical()
        return new_texture

TestApp().run()

You could generalize this by using another Texture, instead of bg_color and setting the transparent Label pixels to the corresponding pixel from the supplied Texture.