I want to realize an animation that transform a circle into a line in Android.
I saw this is possible with AnimatedVectorDrawable and I should use an objectanimator like so to make a path transformation:
<objectAnimator
android:duration="3000"
android:propertyName="pathData"
android:valueFrom="M300,70 l 0,-70 70,70 0,0 -70,70z"
android:valueTo="M300,70 l 0,-70 70,0 0,140 -70,0 z"
android:valueType="pathType"/>
And from the docs if one wants to morph a path into another one, the paths must be compatible for morphing. In more details, the paths should have exact same length of commands , and exact same length of parameters for each commands.
I've started to read this: SVG elliptical arc commands, I think the trick would be to realize a line with some arc/circle commands.
Is there a way to do this, so a line path data can have the same length and same commands as a circle?
Iftah's answer put me on a good track, here is how I did it, it's basically approximating a circle with two cubic Bézier curves (one for the upper half circle and another one for the lower half). A small explanation can be found here.
Code side, here is how it looks:
<?xml version="1.0" encoding="utf-8"?>
<vector xmlns:android="http://schemas.android.com/apk/res/android"
android:width="500dp"
android:height="500dp"
android:viewportWidth="500"
android:viewportHeight="500">
<group>
<path
android:name="circle_line"
android:fillColor="@android:color/black"
android:strokeColor="@android:color/black"
android:strokeWidth="5"
android:pathData="@string/circle_data"/>
</group>
Paths data:
<!-- paths -->
<string name="circle_data">M 125 250 C 137.5 83.34 362.5 83.34 375 250 M 125 250 C 137.5 416.66 362.5 416.66 375 250</string>
<string name="line_data">M 50 250 C 125 250 125 250 250 250 M 250 250 C 375 250 375 250 450 250</string>
The animation works fine, I just have to refine some points in order to customize the animation look.