Cross-platform plumbing for resize-to-client

remoting/host/resizing_host_observer.cc

Index: remoting/host/resizing_host_observer.cc
diff --git a/remoting/host/resizing_host_observer.cc b/remoting/host/resizing_host_observer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..b78cb6ab373bb9c8f47b29b0ea57935ce1719833
--- /dev/null
+++ b/remoting/host/resizing_host_observer.cc
@@ -0,0 +1,158 @@
+// Copyright (c) 2012 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 "remoting/host/resizing_host_observer.h"
+#include "remoting/host/desktop_resizer.h"
+
+#include <set>
+
+#include "base/logging.h"
+
+namespace remoting {
+
+ResizingHostObserver::ResizingHostObserver(
+    DesktopResizer* desktop_resizer, ChromotingHost* host)
+    : desktop_resizer_(desktop_resizer),
+      host_(host),
+      original_size_(SkISize::Make(0, 0)),
+      previous_size_(SkISize::Make(0, 0)) {
+  if (host_) {
+    host_->AddStatusObserver(this);
+  }
+}
+
+ResizingHostObserver::~ResizingHostObserver() {
+  if (host_) {
+    host_->RemoveStatusObserver(this);
+  }
+}
+
+void ResizingHostObserver::OnClientAuthenticated(const std::string& jid) {
+  // Resize-to-client doesn't make sense if multiple clients are connected,
+  // and this is not currently supported anyway.

[Wez, 2012/09/25 20:48:29]

nit: Suggest "This implementation assumes a single connected client, which is
what the host currently supports"; in future we might support multiple clients
but assume that e.g. the first to connect sets the size.

[Jamie, 2012/09/25 23:20:20]

Done.

+  DCHECK(client_jid_.empty());
+  original_size_ = desktop_resizer_->GetCurrentSize();
+  previous_size_ = original_size_;
+}
+
+void ResizingHostObserver::OnClientDisconnected(const std::string& jid) {
+  if (!original_size_.isZero()) {
+    desktop_resizer_->RestoreSize(original_size_);
+    original_size_.set(0, 0);
+  }
+  client_jid_.clear();
+}
+
+class CandidateSize {
+ public:
+  CandidateSize(const SkISize& candidate, const SkISize& preferred)
+      : size_(candidate) {
+    // The client scale factor is the smaller of the candidate:preferred ratios
+    // for width and height.
+    if ((candidate.width() > preferred.width()) ||
+        (candidate.height() > preferred.height())) {
+      float ratio_width =
+          static_cast<float>(preferred.width()) / candidate.width();
+      float ratio_height =
+          static_cast<float>(preferred.height()) / candidate.height();
+      client_scale_factor_ = std::min(ratio_width, ratio_height);
+    } else {
+      // Since clients do not scale up, 1.0 is the maximum.
+      client_scale_factor_ = 1.0;
+    }
+
+    // The aspect ratio "goodness" is defined as being the ratio of the smaller
+    // of the two aspect ratios (candidate and preferred) to the larger. The
+    // best aspect ratio is the one that most closely matches the preferred
+    // aspect ratio (in other words, the ideal aspect ratio "goodness" is 1.0).
+    // By keeping the values < 1.0, it allows ratios the differ in opposite
+    // directions to be compared numerically.
+    float candidate_aspect_ratio =
+        static_cast<float>(candidate.width()) / candidate.height();
+    float preferred_aspect_ratio =
+        static_cast<float>(preferred.width()) / preferred.height();
+    if (candidate_aspect_ratio > preferred_aspect_ratio) {
+      aspect_ratio_goodness_ = preferred_aspect_ratio / candidate_aspect_ratio;
+    } else {
+      aspect_ratio_goodness_ = candidate_aspect_ratio / preferred_aspect_ratio;
+    }
+  }
+
+  const SkISize& size() const { return size_; }
+  float client_scale_factor() const { return client_scale_factor_; }
+  float aspect_ratio_goodness() const { return aspect_ratio_goodness_; }
+  int64 area() const {
+    return static_cast<int64>(size_.width()) * size_.height();
+  }
+
+  bool IsBetterThan(const CandidateSize& other) const {
+    // If either size would require down-scaling, prefer the one that down-
+    // scales the least (since the client scale factor is at most 1.0, this
+    // does not differentiate between sizes that don't require down-scaling).
+    if (client_scale_factor() < other.client_scale_factor()) {
+      return false;
+    } else if (client_scale_factor() > other.client_scale_factor()) {
+      return true;
+    }
+
+    // If the scale factors are the same, pick the size with the largest area.
+    if (area() < other.area()) {
+      return false;
+    } else if (area() > other.area()) {
+      return true;
+    }
+
+    // If the areas are equal, pick the size with the "best" aspect ratio.
+    if (aspect_ratio_goodness() < other.aspect_ratio_goodness()) {
+      return false;
+    } else if (aspect_ratio_goodness() > other.aspect_ratio_goodness()) {
+      return true;
+    }
+
+    // If the aspect ratios are equally good (for example, comparing 640x480
+    // to 480x640 w.r.t. 640x640), just pick the widest, since desktop UIs
+    // are typically design for landscape aspect ratios.
+    return size().width() > other.size().width();
+  }
+
+ private:
+  float client_scale_factor_;
+  float aspect_ratio_goodness_;
+  SkISize size_;
+};
+
+void ResizingHostObserver::OnClientDimensionsChanged(
+    const std::string& jid, const SkISize& preferred_size) {
+  // If the host desktop size changes other than via the resize-to-client
+  // mechanism, then set |previous_size_| to zero and give up. This is an
+  // indication that the user doesn't want resize-to-client.
+  if (previous_size_.isZero()) {

[Wez, 2012/09/25 20:48:29]

nit: I'd prefer that this check be above this comment, so that the comment
appears directly before the |new_size != previous_size_| check, or that it come
immediately after that check, which would match the order of the comment
description.

[Jamie, 2012/09/25 23:20:20]

I want to do this check first because it avoids an unnecessary call to
GetCurrentSize. I've moved the comment.

+    return;
+  }
+  SkISize new_size = desktop_resizer_->GetCurrentSize();
+  if (new_size != previous_size_) {
+    previous_size_ = SkISize::Make(0, 0);
+    return;
+  }
+
+  // If the implementation returns any sizes, pick the best one according to
+  // the algorithm described in CandidateSize::IsBetterThen.
+  std::list<SkISize> sizes =
+      desktop_resizer_->GetSupportedSizes(preferred_size);
+  if (sizes.empty()) {
+    return;
+  }
+  CandidateSize best_size(sizes.front(), preferred_size);
+  std::list<SkISize>::iterator i = sizes.begin();
+  for (++i; i != sizes.end(); ++i) {
+    CandidateSize candidate_size(*i, preferred_size);
+    if (candidate_size.IsBetterThan(best_size)) {
+      best_size = candidate_size;
+    }
+  }
+  previous_size_ = best_size.size();
+  desktop_resizer_->SetSize(previous_size_);
+}
+
+}  // namespace remoting