[Button] Outline of buttons in MaterialButtonToggleGroup are blurred

[mueller-ma]

Description:
I have a MaterialButtonToggleGroup with a three buttons, all with the outline style. The outlines on the outer buttons are blurred, while the outline of the button in middle isn't

Expected behavior:
Please see openhab/openhab-android#1615 (comment) for a photo of this issue. It seems that is happens only on low dpi devices.

Please see openhab/openhab-android#1615 (comment) for a possible explanation for this bug:

My guess would be rounding issues on hdpi devices, since that's the only density which yields a non-integer dp-to-px ratio (1.5 to be precise). This means e.g. 1dp becomes 1.5px, which can be displayed as 1px (too thin) or 2px (too wide).

Source code:
I can reproduce this issue with https://github.com/ricknout/android-mdc-theming, master at 576d0f2e02a599ccbc00b7bc2ee04709f962111a and the following diff:

diff --git a/app/src/main/res/values/styles_button.xml b/app/src/main/res/values/styles_button.xml
index a6ac8df..a52ccfe 100644
--- a/app/src/main/res/values/styles_button.xml
+++ b/app/src/main/res/values/styles_button.xml
@@ -22,10 +22,6 @@
         <item name="textAppearanceButton">@style/AppTextAppearance.Button</item>
         <item name="fontFamily">@font/roboto_mono</item>
         <item name="android:fontFamily">@font/roboto_mono</item>
-        <!-- Global shape attributes -->
-        <item name="shapeAppearanceSmallComponent">@style/AppShapeAppearance.SmallComponent</item>
-        <item name="shapeAppearanceMediumComponent">@style/AppShapeAppearance.MediumComponent</item>
-        <item name="shapeAppearanceLargeComponent">@style/AppShapeAppearance.LargeComponent</item>
         <!-- Button widget style attributes -->
         <item name="materialButtonStyle">@style/AppButton2</item>
         <item name="materialButtonOutlinedStyle">@style/AppOutlinedButton</item>
diff --git a/build.gradle b/build.gradle
index 18bd726..9464d40 100644
--- a/build.gradle
+++ b/build.gradle
@@ -1,5 +1,5 @@
 buildscript {
-    ext.android_gradle_plugin_version = '4.0.0-rc01'
+    ext.android_gradle_plugin_version = '4.0.0'
     ext.kotlin_version = '1.3.72'
     ext.androidx_core_version = "1.3.0-rc01"
     ext.androidx_appcompat_version = "1.2.0-beta01"

Without the patch the outlines of all buttons are blurred.

Android API version:
At least on Android 5.1.1 and 7.1.2

Material Library version:
1.3.0-alpha01

Device:

• Samsung Galaxy Tab PT-P7500
• Fire 7 Tablet

[drchen]

I think it's actually caused by RippleDrawable implementation of Lollipop doesn't correctly propagate drawable state when view is being attached (or under certain corner situations). So buttons in a toggle group look as in "disabled" state, and that's why the outlines are blurred.

Are you sure it also happen on Android 7? I can only reproduce this on Android 5/5.1.