Use Event to render feedback animations.

remoting/android/java/src/org/chromium/chromoting/FeedbackAnimator.java

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.chromoting;
+
+import android.graphics.Color;
+import android.graphics.Paint;
+import android.graphics.Point;
+import android.graphics.RadialGradient;
+import android.graphics.Shader;
+import android.os.SystemClock;
+
+/** Helper class for displaying the press feedback animations. */
+public final class FeedbackAnimator
+        implements Event.ParameterCallback<Boolean, PaintEventParameter> {
+    /** Total duration of the animation, in milliseconds. */
+    private static final float TOTAL_DURATION_MS = 220;
+
+    /** Start time of the animation, from {@link SystemClock#uptimeMillis()}. */
+    private final long mStartTimeInMs;
+
+    /** Contains the size of the feedback animation for the most recent request. */
+    private final float mFeedbackSizeInPixels;
+
+    private final Paint mPaint = new Paint();
+
+    private final Point mPos;
+
+    private FeedbackAnimator(float feedbackSizeInPixels, Point pos) {
+        mStartTimeInMs = SystemClock.uptimeMillis();
+        mFeedbackSizeInPixels = feedbackSizeInPixels;
+        mPos = pos;
+    }
+
+    /** Begins a new animation sequence at position (|pos|). */
+    public static void startAnimation(DesktopView view,
+                                      Point pos,
+                                      DesktopView.InputFeedbackType feedbackType) {
+        if (feedbackType == DesktopView.InputFeedbackType.NONE) {
+            return;
+        }
+
+        view.onPaint().addSelfRemovable(new FeedbackAnimator(
+                getInputFeedbackSizeInPixels(feedbackType), pos));
+    }
+
+    private static float getInputFeedbackSizeInPixels(DesktopView.InputFeedbackType feedbackType) {
+        switch (feedbackType) {
+            case SMALL_ANIMATION:
+                return 40.0f;
+
+            case LARGE_ANIMATION:
+                return 160.0f;
+
+            default:
+                // Unreachable, but required by Google Java style and findbugs.
+                assert false : "Unreached";
+                return 0.0f;
+        }
+    }
+
+    @Override
+    public Boolean run(PaintEventParameter parameter) {
+        float elapsedTimeInMs = SystemClock.uptimeMillis() - mStartTimeInMs;
+        if (elapsedTimeInMs < 1) {
+            return true;
+        }
+
+        // |progress| is 0 at the beginning, 1 at the end.
+        float progress = elapsedTimeInMs / TOTAL_DURATION_MS;
+        if (progress >= 1) {
+            return false;
+        }
+
+        float size = mFeedbackSizeInPixels / parameter.scale;
+
+        // Animation grows from 0 to |size|, and goes from fully opaque to transparent for a
+        // seamless fading-out effect. The animation needs to have more than one color so it's
+        // visible over any background color.
+        float radius = size * progress;
+        int alpha = (int) ((1 - progress) * 0xff);
+
+        int transparentBlack = Color.argb(0, 0, 0, 0);
+        int white = Color.argb(alpha, 0xff, 0xff, 0xff);
+        int black = Color.argb(alpha, 0, 0, 0);
+        mPaint.setShader(new RadialGradient(mPos.x, mPos.y, radius,
+                new int[] {transparentBlack, white, black, transparentBlack},
+                new float[] {0.0f, 0.8f, 0.9f, 1.0f}, Shader.TileMode.CLAMP));
+        parameter.canvas.drawCircle(mPos.x, mPos.y, radius, mPaint);
+        return true;
+    }
+}