how to change the canvas color according to another widget value

[husam alkdary]

It's possible to make the canvas color changes according to another widget value like slider or switch or …..

[Elliot Garbus]

Yes. It’s quite easy. 

For example use a slider to set a kivy numeric property, put the property values in the color field of the canvas. 

Sent from my iPhone

On Apr 12, 2020, at 2:37 PM, husam alkdary <husamal...@gmail.com> wrote:



It's possible to make the canvas color changes according to another widget value like slider or switch or …..

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[husam alkdary]

but I'm using kv language how to set a numerical property 

On Monday, April 13, 2020 at 12:56:10 AM UTC+2, Elliot Garbus wrote:

Yes. It’s quite easy. 

For example use a slider to set a kivy numeric property, put the property values in the color field of the canvas. 

Sent from my iPhone

On Apr 12, 2020, at 2:37 PM, husam alkdary <husamal...@gmail.com> wrote:



It's possible to make the canvas color changes according to another widget value like slider or switch or …..

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[Elliot Garbus]

Two examples below.  Top examples create a class and explicitly declare NumericProperties.

The lower example creates kivy object properties in the kv file.

I prefer to use the NumericProperties directly.

 

 

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.boxlayout import BoxLayout
from kivy.properties import NumericProperty

kv = """
<ColorBox>:
    orientation: 'vertical'
    canvas:
        Color:
            rgb: root.red, root.green, root.blue
        Rectangle:
            size: self.size
            pos: self.pos
    Slider:
        max: 100
        value: 50
        step: 1
        on_value: root.red = self.value/100
    Slider:
        max: 100
        value: 50
        step: 1
        on_value: root.green = self.value/100
    Slider:
        max: 100
        value: 50
        on_value: root.blue = self.value/100

ColorBox:       
"""


class ColorBox(BoxLayout):
    red = NumericProperty(.5)
    green = NumericProperty(.5)
    blue = NumericProperty(.5)


class ColorSlidersApp(App):
    def build(self):
        return Builder.load_string(kv)


ColorSlidersApp().run()

 

 

 

Here is how to do it declaring red, green and blue all in kivy.

 

from kivy.app import App
from kivy.lang import Builder


kv = """
BoxLayout:
    orientation: 'vertical'
    red: 0.5
    green: 0.5
    blue: 0.5
    canvas:
        Color:
            rgb: root.red, root.green, root.blue
        Rectangle:
            size: self.size
            pos: self.pos
    Slider:
        max: 100
        value: 50
        step: 1
        on_value: root.red = self.value/100
    Slider:
        max: 100
        value: 50
        step: 1
        on_value: root.green = self.value/100
    Slider:
        max: 100
        value: 50
        on_value: root.blue = self.value/100
       
"""


class ColorSlidersApp(App):
    def build(self):
        return Builder.load_string(kv)


ColorSlidersApp().run()

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[husam alkdary]

what's on_value mean I can't find it the doc also didn't work with the switch 

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[Elliot Garbus]

Any kivy property creates an associated event.  The event is named on_property_name

If you create a property ‘question’ there will be an event created on_question.  The event will fire with the value of question is changed.

 

In a slider value is the value of the slider, it is a kivy property, and so on_value fires when the value of the slider changes.

A switch uses active, there is an on_active event that fires when the switch state is changed.

 

Read about properties: https://kivy.org/doc/stable/api-kivy.properties.html?highlight=properties#observe-using-on-propname

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[husam alkdary]

if I will use numerical property in side a boxlayout that is inaide a screen inside the root widget which is the screen manager what I should replace the root in 

root.red

I tried to use

 app.root.sm.ids.get_screen('screen name').ids.boxlayout_id.red

but is not working !!

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[Elliot Garbus]

Show the code.  It all depends on how you put the pieces together.

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[husam alkdary]

it's ok I just replace the root with the id of the boxlayout that contain the numerical property amd every thing works fine
thanks

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