Audio indicator: cross platform drawing and animation

chrome/browser/ui/tabs/tab_audio_indicator.cc

+// Copyright (c) 2013 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.
+
+#include "chrome/browser/ui/tabs/tab_audio_indicator.h"
+
+#include "grit/theme_resources.h"
+#include "ui/base/animation/linear_animation.h"
+#include "ui/base/resource/resource_bundle.h"
+#include "ui/gfx/canvas.h"
+#include "ui/gfx/rect.h"
+
+namespace {
+
+// The number of columns to draw for the equalizer graphic.
+const size_t kEqualizerColumnCount = 3;
+
+// The maximum level for the equalizer.
+const size_t kEqualizerMaxLevel = 8;
+
+// The equalizer cycles between these frames. An equalizer frame is 3 columns
+// where each column ranges from 0 to |kEqualizerMaxLevel|. TODO(sail): Replace
+// this with levels from the actual audio source.
+const size_t kEqualizerFrames[][kEqualizerColumnCount] = {
+  { 7, 5, 3 },
+  { 4, 5, 7 },
+  { 4, 2, 5 },
+  { 3, 7, 4 },
+  { 2, 3, 2 },
+  { 3, 4, 3 },
+};
+
+// The duration of each equalizer frame.
+const size_t kAnimationCycleDurationMs = 300;
+
+// The duration of the "ending" animation once audio stops playing.
+const size_t kAnimationEndingDurationMs = 1000;
+
+// Target frames per second. In reality fewer frames are drawn because the
+// equalizer levels change slowly.
+const int kFPS = 15;
+
+}  // namespace
+
+TabAudioIndicator::TabAudioIndicator(Delegate* delegate)
+    : delegate_(delegate),
+      frame_index_(0),
+      state_(STATE_NOT_ANIMATING) {
+}
+
+TabAudioIndicator::~TabAudioIndicator() {
+}
+
+void TabAudioIndicator::SetIsPlayingAudio(bool is_playing_audio) {
+  if (is_playing_audio && state_ != STATE_ANIMATING) {
+    state_ = STATE_ANIMATING;
+    animation_.reset(
+        new ui::LinearAnimation(kAnimationCycleDurationMs, kFPS, this));
+    animation_->Start();
+  } else if (!is_playing_audio && state_ == STATE_ANIMATING) {
+    state_ = STATE_ANIMATION_ENDING;
+    animation_.reset(
+        new ui::LinearAnimation(kAnimationEndingDurationMs, kFPS, this));
+    animation_->Start();
+  }
+}
+
+bool TabAudioIndicator::IsAnimating() {
+  return state_ != STATE_NOT_ANIMATING;
+}
+
+void TabAudioIndicator::Paint(gfx::Canvas* canvas, const gfx::Rect& rect) {
+  if (state_ == STATE_NOT_ANIMATING)
+    return;
+
+  canvas->Save();
+  canvas->ClipRect(rect);
+
+  // Draw 3 equalizer columns. |IDR_AUDIO_EQUALIZER_COLUMN| is a column of the
+  // equalizer with 8 levels. The current level is between 0 and 8 so the
+  // image is shifted down and then drawn.
+  ui::ResourceBundle& rb = ResourceBundle::GetSharedInstance();
+  gfx::ImageSkia* image(rb.GetImageSkiaNamed(IDR_AUDIO_EQUALIZER_COLUMN));
+  int x = rect.x();
+  std::vector<int> levels = GetCurrentEqualizerLevels();
+  for (size_t i = 0; i < levels.size(); ++i) {
+    // Shift the image down by the level. For example, for level 8 draw the
+    // image at rect.y(), For level 7, draw the image at rect.y() - 2, etc...
+    int y = rect.y() + (kEqualizerMaxLevel - levels[i]) * 2;
+    canvas->DrawImageInt(*image, x, y);
+    x += image->width() - 1;
+  }
+
+  canvas->Restore();
+
+  // Cache the levels that were just drawn. This is used to prevent unnecessary
+  // drawing when animation progress doesn't result in equalizer levels
+  // changing.
+  last_displayed_equalizer_levels_ = levels;
+}
+
+void TabAudioIndicator::AnimationProgressed(const ui::Animation* animation) {
+  std::vector<int> levels = GetCurrentEqualizerLevels();
+  if (last_displayed_equalizer_levels_ != levels)
+    delegate_->ScheduleAudioIndicatorPaint();
+}
+
+void TabAudioIndicator::AnimationEnded(const ui::Animation* animation) {
+  if (state_ == STATE_ANIMATING) {
+    // The current equalizer frame animation has finished. Start animating the
+    // next frame.
+    frame_index_ = (frame_index_ + 1) % arraysize(kEqualizerFrames);
+    animation_->Start();
+  } else if (state_ == STATE_ANIMATION_ENDING) {
+    // The "ending" animation has stopped. Update the tab state so that the UI
+    // can update the tab icon.
+    state_ = STATE_NOT_ANIMATING;
+    delegate_->ScheduleAudioIndicatorPaint();
+  }
+}
+
+std::vector<int> TabAudioIndicator::GetCurrentEqualizerLevels() const {
+  int next_frame_index = (frame_index_ + 1) % arraysize(kEqualizerFrames);
+  std::vector<int> levels;
+  // For all 3 columsn of the equalizer, tween between the current equalizer
+  // level and the target equalizer level.
+  for (size_t i = 0; i < kEqualizerColumnCount; ++i) {
+    int start = kEqualizerFrames[frame_index_][i];
+    int end = state_ == STATE_ANIMATION_ENDING
+              ? 0
+              : kEqualizerFrames[next_frame_index][i];
+    levels.push_back(animation_->CurrentValueBetween(start, end));
+  }
+  return levels;
+}