[Remoting Client] DesktopViewport Implementation

remoting/client/desktop_viewport.cc

+// Copyright 2017 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/client/desktop_viewport.h"
+
+#include <algorithm>
+
+#include "base/logging.h"
+
+namespace remoting {
+
+namespace {
+
+float MAX_ZOOM_LEVEL = 100.f;
+
+}  // namespace
+
+DesktopViewport::DesktopViewport() : desktop_to_surface_(0.f, {0.f, 0.f}) {}

[joedow, 2017/04/28 21:29:52]

Add a default c'tor to SimpleMatrix so you don't need to init with zeroes?

[Yuwei, 2017/04/28 23:53:40]

Done.

+
+DesktopViewport::~DesktopViewport() {}
+
+void DesktopViewport::SetDesktopSize(int desktop_width, int desktop_height) {
+  bool need_resize_to_fit = !desktop_size_ready_ && surface_size_ready_;
+  desktop_size_.x = desktop_width;
+  desktop_size_.y = desktop_height;
+  desktop_size_ready_ = true;
+  if (need_resize_to_fit) {
+    ResizeToFit();
+  } else if (IsViewportReady()) {
+    UpdateViewport();
+  }
+}
+
+void DesktopViewport::SetSurfaceSize(int surface_width, int surface_height) {
+  bool need_resize_to_fit = desktop_size_ready_ && !surface_size_ready_;
+  surface_size_.x = surface_width;
+  surface_size_.y = surface_height;
+  surface_size_ready_ = true;
+  if (need_resize_to_fit) {
+    ResizeToFit();
+  } else if (IsViewportReady()) {
+    UpdateViewport();
+  }
+}
+
+void DesktopViewport::ResizeToFit() {
+  if (!IsViewportReady()) {
+    LOG(ERROR) << "Viewport is not ready.";

[joedow, 2017/04/28 21:29:52]

Should this be a DCHECK?  It seems like this is unexpected.

[Yuwei, 2017/04/28 23:53:40]

Done.

+    return;
+  }
+
+  // <---Desktop Width---->

[joedow, 2017/04/28 21:29:52]

I like the ASCII art, I  think it would be good to describe how this works a bit
more.  The gist is that it resizes the desktop such that it fits the viewport in
one dimension.

[Yuwei, 2017/04/28 23:53:40]

Done.

+  // +==========+---------+
+  // |          |         |
+  // | Viewport | Desktop |
+  // |          |         |
+  // +==========+---------+
+  //
+  // +==========+ ^
+  // |          | |
+  // | Viewport | |
+  // |          | |
+  // +==========+ | Desktop
+  // |          | | Height
+  // | Desktop  | |
+  // |          | |
+  // +----------+ v
+
+  float scale = std::max(surface_size_.x / desktop_size_.x,
+                         surface_size_.y / desktop_size_.y);
+  desktop_to_surface_.SetScale(scale);
+  UpdateViewport();
+}
+
+void DesktopViewport::MoveDesktop(float dx, float dy) {
+  desktop_to_surface_.PostTranslate({dx, dy});
+  UpdateViewport();
+}
+
+void DesktopViewport::ScaleDesktop(float px, float py, float scale) {
+  desktop_to_surface_.PostScale({px, py}, scale);
+  UpdateViewport();
+}
+
+void DesktopViewport::SetViewportCenter(float x, float y) {
+  Point old_center = GetViewportCenter();
+  MoveViewportCenterWithoutUpdate(x - old_center.x, y - old_center.y);
+  UpdateViewport();
+}
+
+void DesktopViewport::RegisterOnTransformationChangedCallback(
+    const TransformationCallback& callback,
+    bool run_immediately) {
+  on_transformation_changed_ = callback;
+  if (IsViewportReady() && run_immediately) {
+    callback.Run(desktop_to_surface_.ToMatrixArray());
+  }
+}
+
+bool DesktopViewport::IsViewportReady() const {
+  return desktop_size_ready_ && surface_size_ready_;
+}
+
+void DesktopViewport::UpdateViewport() {
+  // Adjust zoom level.
+  float zoom_level = desktop_to_surface_.GetScale();
+  if (zoom_level > MAX_ZOOM_LEVEL) {
+    // TODO(yuweih): This doesn't account for the effect of the pivot point,
+    //     which will shift the desktop closer to the origin.
+    desktop_to_surface_.SetScale(MAX_ZOOM_LEVEL);
+  }
+
+  Vector2D desktop_size_on_surface_ =
+      desktop_to_surface_.MapVector(desktop_size_);
+  if (desktop_size_on_surface_.x < surface_size_.x &&
+      desktop_size_on_surface_.y < surface_size_.y) {
+    //    +==============+
+    //    |      VP      |      +==========+
+    //    |              |      |    VP    |
+    //    | +----------+ |      +----------+
+    //    | |    DP    | |  ==> |    DP    |
+    //    | +----------+ |      +----------+
+    //    |              |      |          |
+    //    |              |      +==========+
+    //    +==============+
+    // Displayed desktop is too small in both directions, so apply the minimum
+    // zoom level needed to fit either the width or height.
+    float scale = std::min(surface_size_.x / desktop_size_.x,
+                           surface_size_.y / desktop_size_.y);
+    desktop_to_surface_.SetScale(scale);
+  }
+
+  // Adjust position.
+  // Scenarios:
+  // 1. If the viewport can fully fit inside the desktop (smaller or equal width
+  //    and height), but it doesn't overlap with any non-desktop area, it will
+  //    be moved in minimum distance to be fitted inside the desktop.
+  //
+  //    +========+
+  //    | VP     |
+  //    |   +----|--------+     +========+-----+
+  //    |   |    |        |     |        |     |
+  //    +========+        |     |   VP   | DP  |
+  //        |       DP    | ==> |        |     |
+  //        |             |     +========+     |
+  //        |             |     |              |
+  //        +-------------+     +--------------+
+  //
+  // 2. If the viewport is larger than the desktop, the viewport will always
+  //    share the same center as the desktop.
+  //
+  //    +==========+------+==+     +======+------+======+
+  //    | VP       |  DP  |  | ==> | VP   |  DP  |      |
+  //    +==========+------+==+     +======+------+======+
+  //
+  // This is done on the desktop's reference frame to simplify things a bit.
+  Point old_center = GetViewportCenter();
+  Point new_center =
+      ConstrainPointToBounds(GetViewportCenterBounds(), old_center);
+  MoveViewportCenterWithoutUpdate(new_center.x - old_center.x,
+                                  new_center.y - old_center.y);
+
+  if (!on_transformation_changed_.is_null()) {

[joedow, 2017/04/28 21:29:52]

nit: You don't need to call is_null(): 
if (on_transformation_changed_) { on_transformation_changed_.Run(); }

[Yuwei, 2017/04/28 23:53:40]

Done.

+    on_transformation_changed_.Run(desktop_to_surface_.ToMatrixArray());
+  }
+}
+
+Bounds DesktopViewport::GetViewportCenterBounds() const {
+  Bounds bounds;
+
+  // Viewport size on the desktop space.
+  Vector2D viewport_size =
+      desktop_to_surface_.Invert().MapVector(surface_size_);
+
+  // Scenario 1: If VP can fully fit inside the desktop, then VP's center can be
+  // anywhere inside the desktop as long as VP doesn't overlap with the border.
+  bounds.left = viewport_size.x * 0.5f;

[joedow, 2017/04/28 21:29:52]

divide by 2?  I think that is a more natural way to express that you want half
of something.

[Yuwei, 2017/04/28 23:53:40]

Done.

+  bounds.right = desktop_size_.x - viewport_size.x * 0.5f;
+  bounds.top = viewport_size.y * 0.5f;
+  bounds.bottom = desktop_size_.y - viewport_size.y * 0.5f;
+
+  // Scenario 2: If VP can't fully fit inside the desktop in dimension D, then
+  // its bounds in dimension D is tightly restricted to the center of the
+  // desktop.
+  if (bounds.left > bounds.right) {
+    float desktop_width_center = desktop_size_.x * 0.5f;
+    bounds.left = desktop_width_center;
+    bounds.right = desktop_width_center;
+  }
+
+  if (bounds.top > bounds.bottom) {
+    float desktop_height_center = desktop_size_.y * 0.5f;
+    bounds.top = desktop_height_center;
+    bounds.bottom = desktop_height_center;
+  }
+
+  return bounds;
+}
+
+Point DesktopViewport::GetViewportCenter() const {
+  return desktop_to_surface_.Invert().MapPoint(
+      {surface_size_.x * 0.5f, surface_size_.y * 0.5f});
+}
+
+void DesktopViewport::MoveViewportCenterWithoutUpdate(float dx, float dy) {
+  // <dx, dy> is defined on desktop's reference frame. Translation must be
+  // flipped and scaled.
+  desktop_to_surface_.PostTranslate(desktop_to_surface_.MapVector({-dx, -dy}));
+}
+
+}  // namespace remoting