[ProgressIndicator] Added the custom drawable support (1/7)

- Added an interface for indeterminate animator delegate.
- Marked DrawingDelegate to public.

PiperOrigin-RevId: 318084805

lib/java/com/google/android/material/progressindicator/DrawingDelegate.java

@@ -25,7 +25,7 @@
  * A delegate interface for drawing the graphics in different drawable classes used in {@link
  * ProgressIndicator}.
  */
-interface DrawingDelegate {
+public interface DrawingDelegate {
 
   /**
    * Prepares the bound of the canvas for the actual drawing. Should be called before any drawing.

lib/java/com/google/android/material/progressindicator/IndeterminateAnimatorDelegate.java

@@ -0,0 +1,83 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.android.material.progressindicator;
+
+import android.animation.Animator;
+import android.graphics.drawable.Drawable;
+import androidx.annotation.NonNull;
+import androidx.vectordrawable.graphics.drawable.Animatable2Compat.AnimationCallback;
+
+/**
+ * A delegate abstract class for animating properties used in drawing the graphics in different
+ * drawable classes for {@link ProgressIndicator}.
+ */
+public abstract class IndeterminateAnimatorDelegate<T extends Animator> {
+
+  // The drawable associated with this delegate.
+  protected Drawable drawable;
+  // A float array of numbers in [0, 1] representing the positions of ends of each segment on the
+  // track.
+  protected final float[] segmentPositions;
+  // An integer array of displayed colors used for each indicator segment defined by every two
+  // segment positions.
+  protected final int[] segmentColors;
+
+  /**
+   * This constructor should be overridden with other necessary actions, e.g. instantiating the
+   * animator.
+   */
+  protected IndeterminateAnimatorDelegate(int segmentCount) {
+    this.segmentPositions = new float[segmentCount * 2];
+    this.segmentColors = new int[segmentCount];
+  }
+
+  /** Registers the drawable associated to this delegate. */
+  protected void registerDrawable(@NonNull Drawable drawable) {
+    this.drawable = drawable;
+  }
+
+  /** Starts the animator. */
+  abstract void startAnimator();
+
+  /** Cancels the animator immediately. */
+  abstract void cancelAnimatorImmediately();
+
+  /** Requests to cancel the main animator after the current cycle finishes. */
+  abstract void requestCancelAnimatorAfterCurrentCycle();
+
+  /**
+   * Resets all properties controlled by the animator for a fresh start. This should be called after
+   * the drawable is hidden or before the drawable becomes visible.
+   */
+  abstract void resetPropertiesForNewStart();
+
+  /**
+   * Resets all properties controlled by the animator for the next animation cycle. This should be
+   * called between the animation cycles.
+   */
+  abstract void resetPropertiesForNextCycle();
+
+  /**
+   * Registers an {@link AnimationCallback} to the animator for the process what needs to be done
+   * after the current animation cycle.
+   *
+   * @param callback Callback to execute the process at the end of current animation cycle. Note:
+   *     only {@link AnimationCallback#onAnimationEnd(Drawable)} should be overridden. Overriding
+   *     other events may cause undesired result.
+   */
+  abstract void registerAnimatorsCompleteCallback(AnimationCallback callback);
+}