Move all files to natural position.

app/src/main/java/org/thoughtcrime/securesms/animation/AnimationCompleteListener.java

@@ -0,0 +1,17 @@
+package org.thoughtcrime.securesms.animation;
+
+
+import android.animation.Animator;
+
+public abstract class AnimationCompleteListener implements Animator.AnimatorListener {
+  @Override
+  public final void onAnimationStart(Animator animation) {}
+
+  @Override
+  public abstract void onAnimationEnd(Animator animation);
+
+  @Override
+  public final void onAnimationCancel(Animator animation) {}
+  @Override
+  public final void onAnimationRepeat(Animator animation) {}
+}

app/src/main/java/org/thoughtcrime/securesms/animation/DepthPageTransformer.java

@@ -0,0 +1,40 @@
+package org.thoughtcrime.securesms.animation;
+
+import android.view.View;
+
+import androidx.annotation.NonNull;
+import androidx.viewpager.widget.ViewPager;
+
+/**
+ * Based on https://developer.android.com/training/animation/screen-slide#depth-page
+ */
+public final class DepthPageTransformer implements ViewPager.PageTransformer {
+  private static final float MIN_SCALE = 0.75f;
+
+  public void transformPage(@NonNull View view, float position) {
+    final int pageWidth = view.getWidth();
+
+    if (position < -1f) {
+      view.setAlpha(0f);
+
+    } else if (position <= 0f) {
+      view.setAlpha(1f);
+      view.setTranslationX(0f);
+      view.setScaleX(1f);
+      view.setScaleY(1f);
+
+    } else if (position <= 1f) {
+      view.setAlpha(1f - position);
+
+      view.setTranslationX(pageWidth * -position);
+
+      final float scaleFactor = MIN_SCALE + (1f - MIN_SCALE) * (1f - Math.abs(position));
+
+      view.setScaleX(scaleFactor);
+      view.setScaleY(scaleFactor);
+
+    } else {
+      view.setAlpha(0f);
+    }
+  }
+}