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1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #ifndef PPAPI_CPP_VIEW_H_
6 #define PPAPI_CPP_VIEW_H_
7 
8 #include "ppapi/cpp/resource.h"
9 #include "ppapi/cpp/rect.h"
10 #include "ppapi/cpp/size.h"
11 
12 /// @file
13 /// This file defines the API for getting the state of a the view for an
14 /// instance.
15 
16 namespace pp {
17 
18 /// This class represents the state of the view for an instance and contains
19 /// functions for retrieving the current state of that view.
20 class View : public Resource {
21  public:
22   /// Default constructor for creating an is_null() <code>View</code> object.
23   View();
24 
25   /// Creates a View resource, taking and holding an additional reference to
26   /// the given resource handle.
27   View(PP_Resource view_resource);
28 
29   /// GetRect() retrieves the rectangle of the module instance associated
30   /// with a view changed notification relative to the upper-left of the browser
31   /// viewport. This position changes when the page is scrolled.
32   ///
33   /// The returned rectangle may not be inside the visible portion of the
34   /// viewport if the module instance is scrolled off the page. Therefore, the
35   /// position may be negative or larger than the size of the page. The size
36   /// will always reflect the size of the module were it to be scrolled
37   /// entirely into view.
38   ///
39   /// In general, most modules will not need to worry about the position of the
40   ///module instance in the viewport, and only need to use the size.
41   ///
42   /// @return The rectangle of the instance. The default return value for
43   /// an invalid View is the empty rectangle.
44   Rect GetRect() const;
45 
46   /// IsFullscreen() returns whether the instance is currently
47   /// displaying in fullscreen mode.
48   ///
49   /// @return <code>true</code> if the instance is in full screen mode,
50   /// or <code>false</code> if it's not or the resource is invalid.
51   bool IsFullscreen() const;
52 
53   /// IsVisible() determines whether the module instance might be visible to
54   /// the user. For example, the Chrome window could be minimized or another
55   /// window could be over it. In both of these cases, the module instance
56   /// would not be visible to the user, but IsVisible() will return true.
57   ///
58   /// Use the result to speed up or stop updates for invisible module
59   /// instances.
60   ///
61   /// This function performs the duties of GetRect() (determining whether the
62   /// module instance is scrolled into view and the clip rectangle is nonempty)
63   /// and IsPageVisible() (whether the page is visible to the user).
64   ///
65   /// @return <code>true</code> if the instance might be visible to the
66   /// user, <code>false</code> if it is definitely not visible.
67   bool IsVisible() const;
68 
69   /// IsPageVisible() determines if the page that contains the module instance
70   /// is visible. The most common cause of invisible pages is that
71   /// the page is in a background tab in the browser.
72   ///
73   /// Most applications should use IsVisible() instead of this function since
74   /// the module instance could be scrolled off of a visible page, and this
75   /// function will still return true. However, depending on how your module
76   /// interacts with the page, there may be certain updates that you may want
77   /// to perform when the page is visible even if your specific module instance
78   /// is not visible.
79   ///
80   /// @return <code>true</code> if the instance might be visible to the
81   /// user, <code>false</code> if it is definitely not visible.
82   bool IsPageVisible() const;
83 
84   /// GetClipRect() returns the clip rectangle relative to the upper-left corner
85   /// of the module instance. This rectangle indicates the portions of the
86   /// module instance that are scrolled into view.
87   ///
88   /// If the module instance is scrolled off the view, the return value will be
89   /// (0, 0, 0, 0). This clip rectangle does <i>not</i> take into account page
90   /// visibility. Therefore, if the module instance is scrolled into view, but
91   /// the page itself is on a tab that is not visible, the return rectangle will
92   /// contain the visible rectangle as though the page were visible. Refer to
93   /// IsPageVisible() and IsVisible() if you want to account for page
94   /// visibility.
95   ///
96   /// Most applications will not need to worry about the clip rectangle. The
97   /// recommended behavior is to do full updates if the module instance is
98   /// visible, as determined by IsVisible(), and do no updates if it is not
99   /// visible.
100   ///
101   /// However, if the cost for computing pixels is very high for your
102   /// application, or the pages you're targeting frequently have very large
103   /// module instances with small visible portions, you may wish to optimize
104   /// further. In this case, the clip rectangle will tell you which parts of
105   /// the module to update.
106   ///
107   /// Note that painting of the page and sending of view changed updates
108   /// happens asynchronously. This means when the user scrolls, for example,
109   /// it is likely that the previous backing store of the module instance will
110   /// be used for the first paint, and will be updated later when your
111   /// application generates new content with the new clip. This may cause
112   /// flickering at the boundaries when scrolling. If you do choose to do
113   /// partial updates, you may want to think about what color the invisible
114   /// portions of your backing store contain (be it transparent or some
115   /// background color) or to paint a certain region outside the clip to reduce
116   /// the visual distraction when this happens.
117   ///
118   /// @return The rectangle representing the visible part of the module
119   /// instance. If the resource is invalid, the empty rectangle is returned.
120   Rect GetClipRect() const;
121 
122   /// GetDeviceScale returns the scale factor between device pixels and DIPs
123   /// (also known as logical pixels or UI pixels on some platforms). This allows
124   /// the developer to render their contents at device resolution, even as
125   /// coordinates / sizes are given in DIPs through the API.
126   ///
127   /// Note that the coordinate system for Pepper APIs is DIPs. Also note that
128   /// one DIP might not equal one CSS pixel - when page scale/zoom is in effect.
129   ///
130   /// @return A <code>float</code> value representing the number of device
131   /// pixels per DIP.
132   float GetDeviceScale() const;
133 
134   /// GetCSSScale returns the scale factor between DIPs and CSS pixels. This
135   /// allows proper scaling between DIPs - as sent via the Pepper API - and CSS
136   /// pixel coordinates used for Web content.
137   ///
138   /// @return A <code>float</code> value representing the number of DIPs per CSS
139   /// pixel.
140   float GetCSSScale() const;
141 };
142 
143 }  // namespace pp
144 
145 #endif  // PPAPI_CPP_VIEW_H_
146