动态改变矩形颜色

Question

In example below, there are two rectangles drawn in canvas of FloatLayout.

The goal is to create something like a simple pixel art drawing app where the user can draw rectangles and change their color (for example color of rectangle under mouse), so I can't create these rectangles in kv file.

So in this demo example I just want to change the color of rectangle under the mouse.

from kivy.app import App
from kivy.lang import Builder
from kivy.properties import ListProperty
from kivy.graphics import Color, Rectangle

KV = """
FloatLayout
    size_hint: None, None
    size: 512, 512
    on_touch_down: app.test(*args[1].pos)
"""


class MyApp(App):

    color = ListProperty((1,1,1,1))

    def build(self):
        self.root = Builder.load_string(KV)

        self.init_rects()

    def init_rects(self):
        with self.root.canvas:
            x,y = self.root.pos
            w,h = self.root.size

            Color(rgba=(1,1,1,1))
            self.r1 = Rectangle(pos = (x,y), size= (w/2,h))
            Color(rgba=(1,0,0,1))
            self.r2 = Rectangle(pos = (w/2,y), size= (w/2,h))

    def test(self, x,y):
        if x< self.root.center_x:
            print ('I need to color this rectangle (self.r1) to red')
        else:
            print ('I need to color this rectangle (self.r2) to white')

MyApp().run()

In this example I store rectangles as self.r1 and self.r2 (because I think further I will need to change them pos or size)

The problem is I didn't find an example of how to change only one rectangle color, and not to change other colors.

I have a stupid solution (below) - every time to create a new rectangle. But I am sure that this is a bad solution when there will be a lot of rectangles

    def test(self, touch_x, touch_y):
        with self.root.canvas:

            x,y = self.root.pos
            w,h = self.root.size

            if touch_x< self.root.center_x:
                Color(rgba=(1,0,0,1))
                self.r1 = Rectangle(pos = (x,y), size= (w/2,h))
            else:
                Color(rgba=(1,1,1,1))
                self.r2 = Rectangle(pos = (w/2,y), size= (w/2,h))

Roughly speaking I miss something like Rectangle(rgba=...)

What could be the solution in this case?

Answer 1

You can change the Color instead of trying to change the Rectangle . Here is a modification of your code that demonstrates this:

from kivy.app import App
from kivy.lang import Builder
from kivy.properties import ListProperty
from kivy.graphics import Color, Rectangle

KV = """
FloatLayout
    size_hint: None, None
    size: 512, 512
    on_touch_down: app.test(*args[1].pos)
"""


class MyApp(App):

    color = ListProperty((1,1,1,1))

    def build(self):
        self.root = Builder.load_string(KV)

        self.init_rects()

    def init_rects(self):
        with self.root.canvas:
            x,y = self.root.pos
            w,h = self.root.size

            self.c1 = Color(rgba=(1,1,1,1))
            Rectangle(pos = (x,y), size= (w/2,h))
            self.c2 = Color(rgba=(1,0,0,1))
            Rectangle(pos = (w/2,y), size= (w/2,h))

    def test(self, x,y):
        if x< self.root.center_x:
            print ('I need to color this rectangle (self.r1) to red')
            self.c1.rgba = (1,0,0,1)
        else:
            print ('I need to color this rectangle (self.r2) to white')
            self.c2.rgba = (1,1,1,1)

MyApp().run()