Android `background_color` Transparency Fixes #3118

proneon267 · 2025-01-23T07:37:10Z

Originally identified in #2484, this PR separates the changes required to fix the background_color fixes on Android.

Originally posted in: #2484 (comment) :

As I had noted here:

toga/android/src/toga_android/widgets/base.py

Lines 197 to 212 in c9c714e

    
           # Most of the Android Widget have different effects applied them which provide 
        
           # the native look and feel of Android. These widgets' background consists of 
        
           # Drawables like ColorDrawable, InsetDrawable and other animation Effect Drawables 
        
           # like RippleDrawable. Often when such Effect Drawables are used, they are stacked 
        
           # along with other Drawables in a LayerDrawable. 
        
           # 
        
           # LayerDrawable once created cannot be modified and attempting to modify it or 
        
           # creating a new LayerDrawable using the elements of the original LayerDrawable 
        
           # stack, will destroy the native look and feel of the widgets. The original 
        
           # LayerDrawable cannot also be properly cloned. Using `getConstantState()` on the 
        
           # Drawable will produce an erroneous version of the original Drawable. 
        
           # 
        
           # These widgets are also affected by the background color of the parent inside which 
        
           # they are present. Directly, setting background color also destroys the native look 
        
           # and feel of these widgets. Moreover, these effects also serve the purpose of 
        
           # providing visual aid for the action of these widgets.

:

What I meant by that is that in some widgets, for example: toga.Selection, when their background_color is set via set_background_simple then the native effects are lost.
So, if I have:

toga.Box(
            style=Pack(flex=1),
            children=[
                toga.Selection(
                    items=["Alice", "Bob", "Charlie"],
                )
            ],
        )

Then the animation effect on interaction would look like:

But now, if I set a background color on the parent like:

toga.Box(
            style=Pack(flex=1, background_color="#87CEFA"),
            children=[
                toga.Selection(
                    items=["Alice", "Bob", "Charlie"],
                )
            ],
        )

Then the animation effect on interaction would look like:

As we can see, the dropdown arrow is not visible, and the ripple effect is also not visible. Further, the widget doesn't set any background color and hence even setting the parent's background color also destroys the native effects. The same problem exists in other widgets also(like toga.Switch, etc.), where the ripple effect will not be visible:

As I have previously noted in the comment, tampering with the background(LayerDrawable) destroys it and with it the animation effects are also destroyed. Hence, I tried to solve this with ContainedWidget class which doesn't require the existing widgets to be changed.

There is also, toga.DetailedList:

        toga.Box(
            style=Pack(flex=1),
            children=[
                toga.DetailedList(
                    data=[
                        {
                            "icon": toga.Icon("icons/arthur"),
                            "title": "Arthur Dent",
                            "subtitle": "Where's the tea?",
                        },
                        {
                            "icon": toga.Icon("icons/ford"),
                            "title": "Ford Prefect",
                            "subtitle": "Do you know where my towel is?",
                        },
                        {
                            "icon": toga.Icon("icons/tricia"),
                            "title": "Tricia McMillan",
                            "subtitle": "What planet are you from?",
                        },
                    ],
                ),
            ],
        )

But now, if I set a background color on the parent like:

        toga.Box(
            style=Pack(flex=1, background_color="#87CEFA"),
            children=[
                toga.DetailedList(...)
            ],
        )

Similar, problems also exist on other widgets also(like toga.Canvas). Hence, for these widgets also, I have usedContainedWidget class to solve these issues.

PR Checklist:

All new features have been tested
All new features have been documented
I have read the CONTRIBUTING.md file
I will abide by the code of conduct

proneon267 · 2025-01-23T07:40:04Z

Originally posted by @mhsmith in #2484 (comment)

As we can see, the dropdown arrow is not visible, and the ripple effect is also not visible. Further, the widget doesn't set any background color and hence even setting the parent's background color also destroys the native effects.

I can confirm that this also happens Toga 0.4.5, so it wasn't introduced by any of the other changes in this PR [#2484]. if we can understand exactly why the problem is happening, then we'll have a better idea of whether this is the simplest solution.

Widgets shouldn't even be aware of their parent's background. But in this case, the Box isn't actually the Selection's parent at the native level: both of them are direct children of the RelativeLayout, and the Box appears behind the Selection because of their order of creation. So maybe certain background features are being drawn directly on the native parent (the RelativeLayout), and the intervening Box is covering it up? Experimenting with semi-transparent backgrounds may answer this.

It may also have something to do with elevation.

proneon267 · 2025-01-23T07:57:26Z

Readthedocs test failure is unrelated, and is caused due to https://osmfoundation.org/ being down.

proneon267 · 2025-01-23T08:52:55Z

I experimented with semi-transparent backgrounds, to confirm if the arrow and other effects were being drawn on the native parent instead, and @mhsmith was correct:

 toga.Box(
            style=Pack(flex=1, background_color=rgba(135, 206, 250, 0.5)),
            children=[
                toga.Selection(
                    items=["Alice", "Bob", "Charlie"],
                )
            ],
        )

The background features are being drawn directly on the native parent(RelativeLayout), as the Box isn't actually the Selection's parent at the native level: both of them are direct children of the RelativeLayout.

To fix this, I have tried the following, but none of them worked:

Using `setElevation()`:

Note: setElevation() takes values in pixels: http://developer.android.com/reference/android/support/v4/view/ViewCompat.html#setElevation(android.view.View,%20float)

Only setting the elevation of the toga.Selection widget:

selection_widget._impl.native.setElevation(20 * context.getResources().getDisplayMetrics().density)

Setting the elevation of both the toga.Selection and the toga.Box widget:

selection_widget._impl.native.setElevation(20 * context.getResources().getDisplayMetrics().density)
box_widget._impl.native.setElevation(1 * context.getResources().getDisplayMetrics().density)

Setting the elevation of the toga.Selection to positive and the toga.Box widget to negative:

selection_widget._impl.native.setElevation(20 * context.getResources().getDisplayMetrics().density)
box_widget._impl.native.setElevation(-10 * context.getResources().getDisplayMetrics().density)

Using `bringChildToFront()`:

parent = selection_widget._impl.native.getParent()
parent.bringChildToFront(selection_widget._impl.native)

`setTranslationZ()`:

selection_widget._impl.native.setTranslationZ(10.0)

Removing and re-adding to the native parent(RelativeLayout):

parent = selection_widget.impl.native.getParent()
parent.removeView(selection_widget.impl.native)
parent.addView(selection_widget.impl.native)

I had also read somewhere that certain features like shadows are only drawn directly on the native parent. As I have also mentioned previously:

toga/android/src/toga_android/widgets/base.py

Lines 197 to 212 in c9c714e

    
           # Most of the Android Widget have different effects applied them which provide 
        
           # the native look and feel of Android. These widgets' background consists of 
        
           # Drawables like ColorDrawable, InsetDrawable and other animation Effect Drawables 
        
           # like RippleDrawable. Often when such Effect Drawables are used, they are stacked 
        
           # along with other Drawables in a LayerDrawable. 
        
           # 
        
           # LayerDrawable once created cannot be modified and attempting to modify it or 
        
           # creating a new LayerDrawable using the elements of the original LayerDrawable 
        
           # stack, will destroy the native look and feel of the widgets. The original 
        
           # LayerDrawable cannot also be properly cloned. Using `getConstantState()` on the 
        
           # Drawable will produce an erroneous version of the original Drawable. 
        
           # 
        
           # These widgets are also affected by the background color of the parent inside which 
        
           # they are present. Directly, setting background color also destroys the native look 
        
           # and feel of these widgets. Moreover, these effects also serve the purpose of 
        
           # providing visual aid for the action of these widgets.

:
So, it seems like wrapping the native widget inside another view allows us to preserve the native look and feel, while setting the background color of the widgets.

freakboy3742 · 2025-01-24T03:22:30Z

I'll need to defer to @mhsmith for suggestions here - my understanding of the inner workings of Android rendering are hazy at best.

mhsmith · 2025-01-30T17:22:14Z

Thanks, I'll look at this today or tomorrow.

proneon267 · 2025-01-30T17:23:34Z

Thank you :)

mhsmith · 2025-02-03T20:37:57Z

The ripple effects are supposed to be circular, but they're being clipped by their native parent:

It may be possible to fix this with the "clip" properties (https://stackoverflow.com/questions/30626019).

android/src/toga_android/container.py

android/src/toga_android/widgets/base.py

android/src/toga_android/widgets/detailedlist.py

mhsmith · 2025-02-03T23:20:38Z

android/tests_backend/widgets/selection.py

-    @property
-    def background_color(self):
-        xfail("Can't change the background color of Selection on this backend")


This PR enables background colors for quite a few other widgets which didn't support them before. Do their tests also need to be updated?

Yes, the tests should be enabled. However, since background_color is not currently correct on all platforms, so we cannot enable the background color tests on this PR, as the tests would fail on the other platforms(as the fix for those platforms is on separate PRs).

Since, this would lead to a deadlock situation. Hence, I had created #3015 to keep track of the widgets on which all background color tests are not enabled. Once, these background_color fixing PRs are completed, I will enable all background color tests on all platforms.

Co-authored-by: Malcolm Smith <[email protected]>

…popup background color

…edWidget class

proneon267 · 2025-02-04T16:03:55Z

The only remaining currently is the clipping of the ripple effect.

I tried to use the following(on the native_toplevel as well as on other parents like container), but they didn't fix the clipping:

self.native_toplevel.setClipChildren(False)
self.native_toplevel.setClipToPadding(False)
self.native_toplevel.setClipToOutline(False)

However, on further testing, it turns out the problem is due to the incorrect LayoutParams for self.native_toplevel, hence the ripple effect of self.native gets clipped by self.native_toplevel.

Currently, we have:

toga/android/src/toga_android/container.py

Lines 59 to 63 in 8959ff1

    
           def set_content_bounds(self, widget, x, y, width, height): 
        
               lp = RelativeLayout.LayoutParams(width, height) 
        
               lp.topMargin = y 
        
               lp.leftMargin = x 
        
               widget.native_toplevel.setLayoutParams(lp)

toga/android/src/toga_android/widgets/base.py

Lines 218 to 230 in 8959ff1

    
           class ContainedWidget(Widget): 
        
               def __init__(self, interface): 
        
                   super().__init__(interface) 
        
                   self.native_toplevel = RelativeLayout(self._native_activity) 
        
                   self.native_toplevel.addView(self.native) 
        
                   self.native.setLayoutParams( 
        
                       RelativeLayout.LayoutParams( 
        
                           RelativeLayout.LayoutParams.MATCH_PARENT, 
        
                           RelativeLayout.LayoutParams.MATCH_PARENT, 
        
                       ) 
        
                   )

Which produces the clipped ripple effect:

Example source:(The `Selection` widget's background is intentionally kept white)

"""
My first application
"""

import toga
from toga.style import Pack
from toga.style.pack import COLUMN


class HelloWorld(toga.App):
  def reset_to_native_default_background_color(self, widget, **kwargs):
      for widget in self.widgets:
          del widget.style.background_color
      self.content.refresh()

  def startup(self):
      """Construct and show the Toga application.

      Usually, you would add your application to a main content box.
      We then create a main window (with a name matching the app), and
      show the main window.
      """
      self.content = toga.Box(
          style=Pack(
              background_color="#87CEFA",
              direction=COLUMN,
              flex=1,
          ),
          children=[
              toga.Box(style=Pack(flex=1.5)),
              toga.Button(
                  text="Reset to native default background color",
                  on_press=self.reset_to_native_default_background_color,
              ),
              toga.Box(style=Pack(flex=1.5)),
              toga.ImageView(
                  toga.Image(self.paths.app / "resources/imageview.png"),
              ),
              toga.Box(style=Pack(flex=1.5)),
              toga.Label(text="Label"),
              toga.Box(style=Pack(flex=1.5)),
              toga.ProgressBar(max=100, value=50),
              toga.Box(style=Pack(flex=1.5)),
              toga.Selection(
                  items=["Alice", "Bob", "Charlie"],
                  style=Pack(background_color="#ffffff"),
              ),
              toga.Box(style=Pack(flex=1.5)),
              toga.Slider(min=-5, max=10, value=7),
              toga.Box(style=Pack(flex=1.5)),
              toga.NumberInput(value=8908),
              toga.Box(style=Pack(flex=1.5)),
              toga.MultilineTextInput(
                  value="Some text.\nIt can be multiple lines of text."
              ),
              toga.Box(style=Pack(flex=1.5)),
              toga.TextInput(value="Jane Developer"),
              toga.Box(style=Pack(flex=1.5)),
              toga.PasswordInput(value="Jane"),
              toga.Box(style=Pack(flex=1.5)),
              toga.Table(
                  headings=["Name", "Age"],
                  data=[
                      ("Arthur Dent", 42),
                      ("Ford Prefect", 37),
                      ("Tricia McMillan", 38),
                  ],
              ),
              toga.Box(style=Pack(flex=1.5)),
              toga.Switch(text="Switch"),
              toga.Box(style=Pack(flex=1.5)),
              toga.DetailedList(
                  data=[
                      {
                          "icon": toga.Icon("icons/arthur"),
                          "title": "Arthur Dent",
                          "subtitle": "Where's the tea?",
                      },
                      {
                          "icon": toga.Icon("icons/ford"),
                          "title": "Ford Prefect",
                          "subtitle": "Do you know where my towel is?",
                      },
                      {
                          "icon": toga.Icon("icons/tricia"),
                          "title": "Tricia McMillan",
                          "subtitle": "What planet are you from?",
                      },
                  ],
              ),
              toga.Box(style=Pack(flex=1.5)),
              toga.DateInput(),
              toga.Box(style=Pack(flex=1.5)),
              toga.TimeInput(),
              toga.Box(style=Pack(flex=1.5)),
          ],
      )
      self.main_window = toga.MainWindow(title=self.formal_name)
      self.main_window.content = toga.ScrollContainer(content=self.content)
      self.main_window.show()


def main():
  return HelloWorld()

However, logically the correct code should be:

diff --git a/android/src/toga_android/container.py b/android/src/toga_android/container.py
index 714e495ac..d46cabfe3 100644
--- a/android/src/toga_android/container.py
+++ b/android/src/toga_android/container.py
@@ -60,4 +60,4 @@ class Container(Scalable):
         lp = RelativeLayout.LayoutParams(width, height)
         lp.topMargin = y
         lp.leftMargin = x
-        widget.native_toplevel.setLayoutParams(lp)
+        widget.native.setLayoutParams(lp)
diff --git a/android/src/toga_android/widgets/base.py b/android/src/toga_android/widgets/base.py
index 2f4774fca..7cd2eb40c 100644
--- a/android/src/toga_android/widgets/base.py
+++ b/android/src/toga_android/widgets/base.py
@@ -222,10 +222,10 @@ class ContainedWidget(Widget):
         self.native_toplevel = RelativeLayout(self._native_activity)
         self.native_toplevel.addView(self.native)
 
-        self.native.setLayoutParams(
+        self.native_toplevel.setLayoutParams(
             RelativeLayout.LayoutParams(
-                RelativeLayout.LayoutParams.MATCH_PARENT,
-                RelativeLayout.LayoutParams.MATCH_PARENT,
+                RelativeLayout.LayoutParams.WRAP_CONTENT,
+                RelativeLayout.LayoutParams.WRAP_CONTENT,
             )
         )
         # Immediately re-apply styles. Some widgets may defer style application until

But this produces the wrong result:

The native_toplevel should only enclose upto the height of self.native when native_toplevel has WRAP_CONTENT as LayoutParams, but it exceeds beyond the height of self.native. Moreover, the bottom height is also not correct, leading to clipping at the bottom part of the ripple effect.

mhsmith · 2025-02-19T19:47:16Z

I'm not sure why you think this is related to the LayoutParams. Regardless of whether the parent is sized to the child or vice versa, I expect that if the resulting bounds are the same, then the clipping behavior would be the same too.

I tried to use the following(on the native_toplevel as well as on other parents like container), but they didn't fix the clipping:
self.native_toplevel.setClipChildren(False)
self.native_toplevel.setClipToPadding(False)
self.native_toplevel.setClipToOutline(False)

You're right: I tried these methods, plus setClipBounds, on self.native, self.native_toplevel, and Container.native_content, and none of them had any effect. I guess whatever mechanism it's using to draw the ripple on the parent's background, it's being clipped by the parent's bounds regardless of any of these settings. Maybe it worked in 2015 but it doesn't work now.

However, the other comment on the StackOverflow question is apparently still true: "The ripple is drawn on the first parent which doesn't have a null background." In the Android API, null and transparent are not the same. If I change set_background_simple to call:

setBackground(None if color in (None, TRANSPARENT) else ColorDrawable(native_color(color)))

Then when the app requests a transparent background, the ripple is drawn correctly on the native parent (the Container), and when the background is non-transparent, it's clipped on the native_toplevel. I would be willing to accept this, since we don't recommend setting backgrounds on most widgets anyway.

But this still doesn't fix the issue where setting a background color on a Box interferes with the rendering of its children. The only solution I can see to that is to actually reproduce the Toga box hierarchy at the native level, rather than making all widgets direct children of the top-level Container. I'm not sure how difficult that would be, but it would be mostly independent of this PR. So I suggest we limit this PR to fixing the child backgrounds, and make a separate PR later if you want to continue dealing with the parent background bug.

mhsmith · 2025-02-19T17:51:13Z

android/src/toga_android/widgets/base.py

@@ -66,6 +64,7 @@ def __init__(self, interface):
            )
        )

+        self._default_background_color = Color.TRANSPARENT


self._default_background_color is only used in one place, so it might as well be inlined.

mhsmith · 2025-02-19T18:01:13Z

android/src/toga_android/widgets/base.py

@@ -128,33 +131,20 @@ def set_font(self, font):
    # appearance. So each widget must decide how to implement this method, possibly
    # using one of the utility functions below.
    def set_background_color(self, color):
-        pass
+        self.set_background_simple(color)


It should be possible to simplify this even further:

Eliminate set_background_simple and move its content into set_background_color.

Remove all overrides of set_background_color, except for Button and DIvider.

Move the comment about "overwrites other aspects of the widget's appearance" to set_background_filter, and reword it to reflect the current situation.

mhsmith · 2025-02-19T18:05:14Z

android/src/toga_android/colors.py

-CACHE = {TRANSPARENT: Color.TRANSPARENT}
+CACHE = {
+    TRANSPARENT: Color.TRANSPARENT,
+}


There's no need for this reformatting.

mhsmith · 2025-02-19T18:09:46Z

android/tests_backend/widgets/base.py

-        assert self.native.getParent() is container._impl.container.native_content
+        assert (
+            self.native_toplevel.getParent() is container._impl.container.native_content
+        )


This should also check that self.native is either identical to self.native_toplevel, or is a descendant of it.

mhsmith · 2025-02-19T18:12:39Z

android/tests_backend/widgets/base.py

+            # The following complex Drawables all apply color filters to
+            # their children, but they don't implement getColorFilter, at
+            # least not in our current minimum API level.


There's no need for this reformatting – we wrap at 88 columns in this repository.

And likewise with the comment below.

mhsmith · 2025-02-19T18:16:00Z

android/tests_backend/widgets/properties.py

@@ -18,7 +18,7 @@ def toga_color(color_int):
            Color.red(color_int),
            Color.green(color_int),
            Color.blue(color_int),
-            Color.alpha(color_int) / 255,
+            round(Color.alpha(color_int) / 255, 2),


Rounding error should normally be dealt with by using pytest.approx at the location where the value is compared, not by permanently rounding the value itself.

proneon267 and others added 2 commits January 22, 2025 19:41

Fix android background color

2187bb2

Merge branch 'beeware:main' into fix_android_background_color

0d2f4b6

proneon267 added 2 commits January 22, 2025 23:45

Added changenote

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proneon267 and others added 3 commits February 3, 2025 21:00

Update android/src/toga_android/widgets/base.py

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Co-authored-by: Malcolm Smith <[email protected]>

Fix pre commit issues

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Merge branch 'beeware:main' into fix_android_background_color

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proneon267 mentioned this pull request Feb 4, 2025

Fix un-selection background color on Android DetailedList and Table #3156

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Refactor according to review

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Remove changes related to beeware#3156 and disable setting Selection …

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…popup background color

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Android `background_color` Transparency Fixes #3118

Android `background_color` Transparency Fixes #3118

proneon267 commented Jan 23, 2025 •

edited by mhsmith

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edited by mhsmith

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Only setting the elevation of the `toga.Selection` widget:

Setting the elevation of both the `toga.Selection` and the `toga.Box` widget:

Setting the elevation of the `toga.Selection` to positive and the `toga.Box` widget to negative:

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	# Most of the Android Widget have different effects applied them which provide
	# the native look and feel of Android. These widgets' background consists of
	# Drawables like ColorDrawable, InsetDrawable and other animation Effect Drawables
	# like RippleDrawable. Often when such Effect Drawables are used, they are stacked
	# along with other Drawables in a LayerDrawable.
	#
	# LayerDrawable once created cannot be modified and attempting to modify it or
	# creating a new LayerDrawable using the elements of the original LayerDrawable
	# stack, will destroy the native look and feel of the widgets. The original
	# LayerDrawable cannot also be properly cloned. Using `getConstantState()` on the
	# Drawable will produce an erroneous version of the original Drawable.
	#
	# These widgets are also affected by the background color of the parent inside which
	# they are present. Directly, setting background color also destroys the native look
	# and feel of these widgets. Moreover, these effects also serve the purpose of
	# providing visual aid for the action of these widgets.

Android background_color Transparency Fixes #3118

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Android background_color Transparency Fixes #3118

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proneon267 commented Jan 23, 2025 • edited by mhsmith Loading

Originally posted in: #2484 (comment) :

PR Checklist:

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Using setElevation():

Only setting the elevation of the toga.Selection widget:

Setting the elevation of both the toga.Selection and the toga.Box widget:

Setting the elevation of the toga.Selection to positive and the toga.Box widget to negative:

Using bringChildToFront():

setTranslationZ():

Removing and re-adding to the native parent(RelativeLayout):

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Android `background_color` Transparency Fixes #3118

Android `background_color` Transparency Fixes #3118

proneon267 commented Jan 23, 2025 •

edited by mhsmith

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Using `setElevation()`:

Only setting the elevation of the `toga.Selection` widget:

Setting the elevation of both the `toga.Selection` and the `toga.Box` widget:

Setting the elevation of the `toga.Selection` to positive and the `toga.Box` widget to negative:

Using `bringChildToFront()`:

`setTranslationZ()`:

proneon267 Feb 4, 2025 •

edited

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proneon267 commented Feb 4, 2025 •

edited by mhsmith

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mhsmith commented Feb 19, 2025 •

edited

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