[Remoting Client] DesktopViewport Implementation

remoting/client/desktop_viewport.h

+// 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.
+
+#ifndef REMOTING_CLIENT_DESKTOP_VIEWPORT_H_
+#define REMOTING_CLIENT_DESKTOP_VIEWPORT_H_
+
+#include "base/callback.h"
+#include "remoting/client/view_matrix.h"
+
+namespace remoting {
+
+// The viewport is a sliding window on the desktop image. This class defines
+// the viewport's position and size, provides methods to manipulate it, and
+// outputs a desktop space -> surface space transformation matrix for drawing
+// the desktop onto the client's view surface on the screen.
+//
+// Desktop space: Coordinates to locate a point on the host's desktop image in
+//     pixels, similar to the mouse's cursor position.
+// Surface space: Coordinates to locate a point on the client device's view
+//     surface (e.g. GLKView/SurfaceView) for rendering the desktop, this is
+//     often the coordinate system to locate a point on the user's phone
+//     screen (if the surface expands to the whole screen).
+//
+// Viewport: Projection of the user surface view on the desktop space.
+// Desktop: Projection of the host's desktop on the surface space.
+//
+// You may either manipulate the desktop on the surface coordinate or manipulate
+// the viewport on the desktop coordinate, depending on your choice of the
+// reference frame.
+class DesktopViewport {
+ public:
+  using TransformationCallback = base::Callback<void(const ViewMatrix&)>;
+
+  DesktopViewport();
+  ~DesktopViewport();
+
+  // Sets the |desktop_size_| and initializes the viewport when necessary.
+  void SetDesktopSize(int desktop_width, int desktop_height);
+
+  // Sets the |surface_size_| and initializes the viewport when necessary.
+  void SetSurfaceSize(int surface_width, int surface_height);
+
+  // Translates the desktop on the surface's reference frame by <dx, dy>.
+  void MoveDesktop(float dx, float dy);
+
+  // Scales the desktop on the surface's reference frame at pivot point (px, py)
+  // by |scale|.
+  void ScaleDesktop(float px, float py, float scale);
+
+  // Sets the viewport center to (x, y) on the desktop's coordinate.
+  void SetViewportCenter(float x, float y);
+
+  // Registers the callback to be called once the transformation has changed.
+  // run_immediately: If true and the viewport is ready to be used, the callback
+  //     will be called immedately with the transformation matrix.
+  void RegisterOnTransformationChangedCallback(
+      const TransformationCallback& callback,
+      bool run_immediately);
+
+ private:
+  struct Bounds {
+    float left;
+    float right;
+    float top;
+    float bottom;
+  };
+
+  // Resizes the desktop such that the image is displayed without borders in
+  // minimum possible zoom-level. This will be called once both the desktop
+  // and the surface size are set.
+  void ResizeToFit();
+
+  // True if desktop size and surface size are set.
+  bool IsViewportReady() const;
+
+  // Adjusts the size and position of the viewport so that the constrains always
+  // hold, then feed the matrix to |on_transformation_changed_|.
+  void UpdateViewport();
+
+  // Gets a rectangle of all possible positions where the viewport's center can
+  // locate.
+  Bounds GetViewportCenterBounds() const;
+
+  // Returns the current center of the viewport on the desktop's coordinate.
+  ViewMatrix::Point GetViewportCenter() const;
+
+  // Translates the viewport on the desktop's reference frame by <dx, dy>,
+  // without calling UpdateViewport().
+  void MoveViewportCenterWithoutUpdate(float dx, float dy);
+
+  // Moves the point inside the bounds with minimum displacement if it is out of
+  // the bounds.
+  static ViewMatrix::Point ConstrainPointToBounds(
+      const Bounds& bounds,
+      const ViewMatrix::Point& point);
+
+  ViewMatrix::Vector2D desktop_size_;
+  ViewMatrix::Vector2D surface_size_;
+
+  bool desktop_size_ready_ = false;
+  bool surface_size_ready_ = false;
+
+  ViewMatrix desktop_to_surface_transform_;
+
+  TransformationCallback on_transformation_changed_;
+
+  // DesktopViewport is neither copyable nor movable.
+  DesktopViewport(const DesktopViewport&) = delete;
+  DesktopViewport& operator=(const DesktopViewport&) = delete;
+};
+
+}  // namespace remoting
+#endif  // REMOTING_CLIENT_DESKTOP_VIEWPORT_H_