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diff --git a/examples/widgets/doc/padnavigator.qdoc b/examples/widgets/doc/padnavigator.qdoc new file mode 100644 index 0000000000..8b1da516b5 --- /dev/null +++ b/examples/widgets/doc/padnavigator.qdoc @@ -0,0 +1,583 @@ +/**************************************************************************** +** +** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies). +** Contact: http://www.qt-project.org/ +** +** This file is part of the documentation of the Qt Toolkit. +** +** $QT_BEGIN_LICENSE:FDL$ +** GNU Free Documentation License +** Alternatively, this file may be used under the terms of the GNU Free +** Documentation License version 1.3 as published by the Free Software +** Foundation and appearing in the file included in the packaging of +** this file. +** +** Other Usage +** Alternatively, this file may be used in accordance with the terms +** and conditions contained in a signed written agreement between you +** and Nokia. +** +** +** +** +** +** $QT_END_LICENSE$ +** +****************************************************************************/ + +/*! + \example graphicsview/padnavigator + \title Pad Navigator Example + + The Pad Navigator Example shows how you can use Graphics View together with + embedded widgets and Qt's \l{State Machine Framework} to create a simple + but useful, dynamic, animated user interface. + + \image padnavigator-example.png + + The interface consists of a flippable, rotating pad with icons that can be + selected using the arrow keys on your keyboard or keypad. Pressing enter + will flip the pad around and reveal its back side, which has a form + embedded into a QGraphicsProxyWidget. You can interact with the form, and + press the enter key to flip back to the front side of the pad at any time. + + Graphics View provides the QGraphicsScene class for managing and + interacting with a large number of custom-made 2D graphical items derived + from the QGraphicsItem class, and a QGraphicsView widget for visualizing + the items, with support for zooming and rotation. + + This example consists of a \c RoundRectItem class, a \c FlippablePad class, + a \c PadNavigator class, a \c SplashItem class, and a \c main() function. + + \section1 RoundRectItem Class Definition + + The \c RoundRectItem class is used by itself to display the icons on the + pad, and as a base class for \c FlippablePad, the class for the pad itself. + The role of the class is to paint a round rectangle of a specified size and + gradient color, and optionally to paint a pixmap icon on top. To support \c + FlippablePad it also allows filling its contents with a plain window + background color. + + Let's start by reviewing the \c RoundRectItem class declaration. + + \snippet graphicsview/padnavigator/roundrectitem.h 0 + + \c RoundRectItem inherits QGraphicsObject, which makes it easy to control + its properties using QPropertyAnimation. Its constructor takes a rectangle + to determine its bounds, and a color. + + Besides implementing the mandatory \l{QGraphicsItem::paint()}{paint()} and + \l{QGraphicsItem::boundingRect()}{boundingRect()} pure virtual functions, + it also provides the \c pixmap and \c fill properties. + + The \c pixmap property sets an optional pixmap that is drawn on top of the + round rectangle. The \c fill property will, when true, fill the round + rectangle contents with a fixed QPalette::Window background color. + Otherwise the contents are filled using a gradient based on the color + passed to \c RoundRectItem's constructor. + + \snippet graphicsview/padnavigator/roundrectitem.h 1 + + The private data members are: + + \list + \li \c pix: The optional pixmap that is drawn on top of the rectangle. + \li \c fillRect: Corresponds to the \c fill property. + \li \c color: The configurable gradient color fill of the rectangle. + \li \c bounds: The bounds of the rectangle. + \li \c gradient: A precalculated gradient used to fill the rectangle. + \endlist + + We will now review the \c RoundRectItem implementation. Let's start by + looking at its constructor: + + \snippet graphicsview/padnavigator/roundrectitem.cpp 0 + + The constructor initializes its member variables and forwards the \c parent + argument to QGraphicsObject's constructor. It then constructs the linear + gradient that is used in \l{QGraphicsItem::paint()}{paint()} to draw the + round rectangle's gradient background. The linear gradient's starting point + is at the top-left corner of the bounds, and the end is at the bottom-left + corner. The start color is identical to the color passed as an argument, + and a slightly darker color is chosen for the final stop. + + We store this gradient as a member variable to avoid having to recreate the + gradient every time the item is repainted. + + Finally we set the cache mode + \l{QGraphicsItem::ItemCoordinateCache}{ItemCoordinateCache}. This mode + causes the item's rendering to be cached into an off-screen pixmap that + remains persistent as we move and transform the item. This mode is ideal + for this example, and works particularly well with OpenGL and OpenGL ES. + + \snippet graphicsview/padnavigator/roundrectitem.cpp 1 + + The \c pixmap property implementation simple returns the member pixmap, or + sets it and then calls \l{QGraphicsItem::update()}{update()}. + + \snippet graphicsview/padnavigator/roundrectitem.cpp 2 + + As the \l{QGraphicsItem::paint()}{paint()} implementation below draws a + simple drop shadow down and to the right of the item, we return a slightly + adjusted rectangle from \l{QGraphicsItem::boundingRect()}{boundingRect()}. + + \snippet graphicsview/padnavigator/roundrectitem.cpp 3 + + The \l{QGraphicsItem::paint()}{paint()} implementation starts by rendering + a semi transparent black round rectangle drop shadow, two units down and to + the right of the main item. + + \snippet graphicsview/padnavigator/roundrectitem.cpp 4 + + We then draw the "foreground" round rectangle itself. The fill depends on + the \c fill property; if true, we will with a plain QPalette::Window color. + We get the current brush from QApplication::palette(). We assign a single + unit wide pen for the stroke, assign the brush, and then draw the + rectangle. + + \snippet graphicsview/padnavigator/roundrectitem.cpp 5 + + If a pixmap has been assigned to the \e pixmap property, we draw this + pixmap in the center of the rectangle item. The pixmaps are scaled to match + the size of the icons; in arguably a better approach would have been to + store the icons with the right size in the first places. + + \snippet graphicsview/padnavigator/roundrectitem.cpp 6 + + Finally, for completeness we include the \c fill property implementation. + It returns the \c fill member variable's value, and when assigned to, it + calls \l{QGraphicsItem::update()}{update()}. + + As mentioned already, \c RoundRectItem is the base class for \c + FlippablePad, which is the class representing the tilting pad itself. We + will proceed to reviewing \c FlippablePad. + + \section1 FlippablePad Class Definition + + \c FlippablePad is, in addition to its inherited \c RoundRectItem + responsibilities, responsible for creating and managing a grid of icons. + + \snippet graphicsview/padnavigator/flippablepad.h 0 + + Its declaration is very simple: It inherits \c RoundRectItem and does not + need any special polymorphic behavior. It's suitable to declare its own + constructor, and a getter-function that allows \c PadNavigator to access + the icons in the grid by (row, column). + + The example has no "real" behavior or logic of any kind, and because of + that, the icons do not need to provide any \e behavior or special + interactions management. In a real application, however, it would be + natural for the \c FlippablePad and its icons to handle more of the + navigation logic. In this example, we have chosen to leave this to + the \c PadNavigator class, which we will get back to below. + + We will now review the \c FlippablePad implementation. This implementation + starts with two helper functions: \c boundsFromSize() and \c + posForLocation(): + + \snippet graphicsview/padnavigator/flippablepad.cpp 0 + + \c boundsForSize() takes a QSize argument, and returns the bounding + rectangle of the flippable pad item. The QSize determines how many rows and + columns the icon grid should have. Each icon is given 150x150 units of + space, and this determines the bounds. + + \snippet graphicsview/padnavigator/flippablepad.cpp 1 + + \c posForLocation() returns the position of an icon given its row and + column position. Like \c boundsForSize(), the function assumes each icon is + given 150x150 units of space, and that all icons are centered around the + flippable pad item's origin (0, 0). + + \snippet graphicsview/padnavigator/flippablepad.cpp 2 + + The \c FlippablePad constructor passes suitable bounds (using \c + boundsForSize()) and specific color to \c RoundRectItem's constructor. + + \snippet graphicsview/padnavigator/flippablepad.cpp 3 + + It then loads pixmaps from compiled-in resources to use for its icons. + QDirIterator is very useful in this context, as it allows us to fetch all + resource "*.png" files inside the \c :/images directory without explicitly + naming the files. + + We also make sure not to load more pixmaps than we need. + + \snippet graphicsview/padnavigator/flippablepad.cpp 4 + + Now that we have the pixmaps, we can create icons, position then and assign + pixmaps. We start by finding a suitable size and color for the icons, and + initializing a convenient grid structure for storing the icons. This \c + iconGrid is also used later to find the icon for a specific (column, row) + location. + + For each row and column in our grid, we proceed to constructing each icon + as an instance of \c RoundRectItem. The item is placed by using the \c + posForLocation() helper function. To make room for the slip-behind + selection item, we give each icon a \l{QGraphicsItem::zValue()}{Z-value} of + 1. The pixmaps are distributed to the icons in round-robin fasion. + + Again, this approach is only suitable for example purposes. In a real-life + application where each icon represents a specific action, it would be more + natural to assign the pixmaps directly, or that the icons themselves + provide suitable pixmaps. + + \snippet graphicsview/padnavigator/flippablepad.cpp 5 + + Finally, the \c iconAt() function returns a pointer to the icon at a + specific row and column. It makes a somewhat bold assumption that the input + is valid, which is fair because the \c PadNavigator class only calls this + function with correct input. + + We will now review the \c SplashItem class. + + \section1 SplashItem Class Definition + + The \c SplashItem class represents the "splash window", a semitransparent + white overlay with text that appears immediately after the application has + started, and disappears after pressing any key. The animation is controlled + by \c PadNavigator; this class is very simple by itself. + + \snippet graphicsview/padnavigator/splashitem.h 0 + + The class declaration shows that \c SplashItem inherits QGraphicsObject to + allow it to be controlled by QPropertyAnimation. It reimplements the + mandatory \l{QGraphicsItem::paint()}{paint()} and + \l{QGraphicsItem::boundingRect()}{boundingRect()} pure virtual functions, + and keeps a \c text member variable which will contain the information text + displayed on this splash item. + + Let's look at its implementation. + + \snippet graphicsview/padnavigator/splashitem.cpp 0 + + The constructor forwards to QGraphicsObject as expected, assigns a text + message to the \c text member variable, and enables + \l{QGraphicsItem::DeviceCoordinateCache}{DeviceCoordinateCache}. This cache + mode is suitable because the splash item only moves and is never + transformed, and because it contains text, it's important that it has a + pixel perfect visual appearance (in constrast to + \l{QGraphicsItem::ItemCoordinateCache}{ItemCoordinateCache}, where the + visual appearance is not as good). + + We use caching to avoid having to relayout and rerender the text for each + frame. An alterative approach would be to use the new QStaticText class. + + \snippet graphicsview/padnavigator/splashitem.cpp 1 + + \c SplashItem's bounding rectangle is fixed at (400x175). + + \snippet graphicsview/padnavigator/splashitem.cpp 2 + + The \l{QGraphicsItem::paint()}{paint()} implementation draws a clipped + round rectangle with a thick 2-unit border and a semi-transparent white + background. It proceeds to finding a suitable text area by adjusting the + splash item's bounding rectangle with 10 units in each side. The text is + rendered inside this rectangle, with top-left alignment, and with word + wrapping enabled. + + The main class now remains. We will proceed to reviewing \c PadNavigator. + + \section1 PadNavigator Class Definition + + \c PadNavigator represents the main window of our Pad Navigator Example + application. It creates and controls a somewhat complex state machine, and + several animations. Its class declaration is very simple: + + \snippet graphicsview/padnavigator/padnavigator.h 0 + + It inherits QGraphicsView and reimplements only one function: + \l{QGraphicsView::resizeEvent()}{resizeEvent()}, to ensure the scene is + scaled to fit inside the view when resizing the main window. + + The \c PadNavigator constructor takes a QSize argument that determines the + number or rows and columns in the grid. + + It also keeps a private member instance, \c form, which is the generated + code for the pad's back side item's QGraphicsProxyWidget-embedded form. + + \snippet graphicsview/padnavigator/padnavigator.cpp 0 + + \c PadNavigator's constructor is a bit long. In short, its job is to create + all items, including the \c FlippablePad, the \c SplashItem and the + QGraphicsProxyWidget \c backItem, and then to set up all animations, states + and transitions that control the behavior of the application. + + It starts out simple, by forwarding to QGraphicsView's constructor. + + \snippet graphicsview/padnavigator/padnavigator.cpp 1 + + The first item to be created is \c SplashItem. This is going to be a top-level + item in the scene, next to \c FlippablePad, and stacked on top of it, so we + assign it a \l{QGraphicsItem::zValue()}{Z-value} of 1. + + \snippet graphicsview/padnavigator/padnavigator.cpp 2 + + Now we construct the \c FlippablePad item, passing its column-row count to + its constructor. + + The pad is controlled by three transformations, and we create one + QGraphicsRotation object for each of these. + + \list + \li \c flipRotation: Rotates the grid around its Qt::YAxis. This rotation is + animated from 0 to 180, and eventually back, when enter is pressed on the + keyboard, flipping the pad around. + \li \c xRotation: Rotates the grid around its Qt::XAxis. This is used to + tilt the pad vertically corresponding to which item is currently selected. + This way, the selected item is always kept in front. + \li \c yRotation: Rotates the grid around its Qt::YAxis. This is used to + tilt the pad horizontally corresponding to which item is selected. This + way, the selected item is always kept in front. + \endlist + + The combination of all three rotations is assigned via + QGraphicsItem::setTransformations(). + + \snippet graphicsview/padnavigator/padnavigator.cpp 3 + + Now we construct the QGraphicsProxyWidget-embedded \c backItem. The proxy + widget is created as a child of the pad. We create a new QWidget and + populate it with the \c form member. To ensure the \c hostName line edit is + the first to receive input focus when this item is shown, we call + \l{QWidget::setFocus()}{setFocus()} immediately. This will not give the + widget focus right away; it will only prepare the item to automatically + receive focus once it is shown. + + The QWidget based form is embedded into the proxy widget. The proxy is + hidden initially; we only want to show it when the pad is rotated at least + 90 degrees, and we also rotate the proxy itself by 180 degrees. This way we + give the impression that the proxy widget is "behind" the flipped pad, when + in fact, it's actually \e{on top of it}. + + We enable \l{QGraphicsItem::ItemCoordinateCache}{ItemCoordinateCache} to + ensure the flip animation can run smoothly. + + \snippet graphicsview/padnavigator/padnavigator.cpp 4 + + We now create the selection item. This is simply another instance of \c + RoundRectItem that is slightly larger than the icons on the pad. We create + it as an immediate child of the \c FlippablePad, so the selection item is a + sibling to all the icons. By giving it a + \l{QGraphicsItem::zValue()}{Z-value} of 0.5 we ensure it will slide between + the pad and its icons. + + What follows now is a series of animation initializations. + + \snippet graphicsview/padnavigator/padnavigator.cpp 5 + + We begin with the animations that apply to the splash item. The first + animation, \c smoothSplashMove, ensures that the "y" property of \c splash + will be animated with a 250-millisecond duration + \l{QEasingCurve::InQuad}{InQuad} easing function. \c smoothSplashOpacity + ensures the opacity of \c splash eases in and out in 250 milliseconds. + + The values are assigned by \c PadNavigator's state machine, which is + created later. + + \snippet graphicsview/padnavigator/padnavigator.cpp 6 + + These are the animations that control the selection item's movement and the + \c xRotation and \c yRotation QGraphicsRotation objects that tilt the pad. + All animations have a duration of 125 milliseconds, and they all use the + \l{QEasingCurve::InOutQuad}{InOutQuad} easing function. + + \snippet graphicsview/padnavigator/padnavigator.cpp 7 + + We now create the animations that control the flip-effect when you press + the enter key. The main goal is to rotate the pad by 180 degrees or back, + but we also need to make sure the selection item's tilt rotations are reset + back to 0 when the pad is flipped, and restored back to their original + values when flipped back: + + \list + \li \c smoothFlipRotation: Animates the main 180 degree rotation of the pad. + \li \c smoothFlipScale: Scales the pad out and then in again while the pad is rotating. + \li \c smoothFlipXRotation: Animates the selection item's X-tilt to 0 and back. + \li \c smoothFlipYRotation: Animates the selection item's Y-tilt to 0 and back. + \li \c flipAnimation: A parallel animation group that ensures all the above animations are run in parallel. + \endlist + + All animations are given a 500 millisecond duration and an + \l{QEasingCurve::InOutQuad}{InOutQuad} easing function. + + It's worth taking a close look at \c smoothFlipScale. This animation's + start and end values are both 1.0, but at animation step 0.5 the + animation's value is 0.7. This means that after 50% of the animation's + duration, or 250 milliseconds, the pad will be scaled down to 0.7x of its + original size, which gives a great visual effect while flipping. + + \snippet graphicsview/padnavigator/padnavigator.cpp 8 + + This section uses a trick to ensure that certain properties are assigned + precisely when the flip animation passes 50%, or 90 degrees, rotation. In + short, the pad's icons and selection item are all hidden, the pad's \c fill + property is enabled, and \c backItem is shown when flipping over. When + flipping back, the reverse properties are applied. + + The way this is achieved is by running a sequential animation in parallel + to the other animations. This sequence, dubbed \c setVariablesSequence, + starts with a 250 millisecond pause, and then executes several animations + with a duration of 0. Each animation will ensure that properties are set + immediate at this point. + + This approach can also be used to call functions or set any other + properties at a specific time while an animation is running. + + \snippet graphicsview/padnavigator/padnavigator.cpp 9 + + We will now create the state machine. The whole \c PadNavigator state + machinery is controlled by one single state machine that has a + straight-forward state structure. The state engine itself is created + as a child of the \c PadNavigator itself. We then create three top level + states: + + \list + \li \c splashState: The initial state where the splash item is visible. + \li \c frontState: The base state where the splash is gone and we can see + the front side of the pad, and navigate the selection item. + \li \c backState: The flipped state where the \c backItem is visible, and we + can interact with the QGraphicsProxyWidget-embedded form. + \endlist + + \snippet graphicsview/padnavigator/padnavigator.cpp 10 + + Each state assigns specific properties to objects on entry. Most + interesting perhaps is the assignment of the value 0.0 to the pad's \c + flipRotation angle property when in \c frontState, and 180.0 when in \c + backState. At the end of this section we register default animations with + the state engine; these animations will apply to their respective objects + and properties for any state transition. Otherwise it's common to assign + animations to specific transitions. + + The \c splashState state is set as the initial state. This is required + before we start the state engine. We proceed with creating some + transitions. + + \snippet graphicsview/padnavigator/padnavigator.cpp 11 + + QEventTransition defines a very flexible transition type. You can use this + class to trigger a transition based on an object receiving an event of a + specific type. In this case, we would like to transition from \c + splashState into \c frontState if \c PadNavigator receives any key press + event (QEvent::KeyPress). + + We register the \c splashItem's animations to this transition to ensure they + are used to animate the item's movement and opacity. + + \snippet graphicsview/padnavigator/padnavigator.cpp 12 + + We use QKeyEventTransition to capture specific key events. In this case, we + detect that the user presses Qt::Key_Return or Qt::Key_Enter, and use this + to trigger transitions between \c frontState and backState. We register \c + flipAnimation, our complex parallel animation group, with these + transitions. + + We continue by defining the states for each of the icons in the grid. + + \snippet graphicsview/padnavigator/padnavigator.cpp 13 + + We will use state groups to control transitions between icons. Each icon + represents a \e substate of \c frontState. We will then define transitions + between the states by detecting key presses, using QKeyEventTransition. + + We start by creating all the substates, and at the same time we create a + temporary grid structure for the states to make it easier to find which + states represents icons that are up, down, left and to the right each + other. + + Once the first substate is known, we set this up as the initial substate of + \c frontState. We will use the (0, 0), or top-left, icon for the initial + substate. We initialze the selection item's position to be exactly where + the top-left icon is. + + \snippet graphicsview/padnavigator/padnavigator.cpp 14 + + We can now create four transitions for each icon. Each transition ensures + that we move to the state corresponding to which arrow key has been + pressed. It's clear from this techinique that we could design any other + specific transitions to and from each of the sub states depending on these + and other keys. + + \snippet graphicsview/padnavigator/padnavigator.cpp 15 + + Also, for each of the icons, we assign suitable values to the \c xRotation + and \c yRotation objects' "angle"-properties. If you recall, these + properties "tilt" the pad corresponding to which item is currently + selected. We ensure each icon is invisible when the pad is flipped, and + visible when the pad is not flipped. To ensure the visible property is + assigned at the right time, we add property-controlling animations to the + \c setVariableSequence animation defined earlier. + + \snippet graphicsview/padnavigator/padnavigator.cpp 16 + + We are now finished with all states, transitions, and animations. We now + create the scene that will contain all our items. The scene gets a defined + background pixmap, and we disable item indexing (as most items in this + scene are animated). We add our \c pad item to the scene, and use its + bounding rectangle to fixate the scene rectangle. This rectangle is used by + the view to find a suitable size for the application window. + + Then the scene is assigned to the view, or in our case, \c PadNavigator + itself. + + \snippet graphicsview/padnavigator/padnavigator.cpp 17 + + Now that the scene has received its final size, we can position the splash + item at the very top, find its fade-out position, and add it to the scene. + + \snippet graphicsview/padnavigator/padnavigator.cpp 18 + + The view toggles a few necessary properties: + + \list + \li It disables its scroll bars - this application has no use for scroll bars. + \li It assigns a minimum size. This is necessary to avoid numerical errors + in our fit-in-view \c resizeEvent() implementation. + \li It sets \l{QGraphicsView::FullViewportUpdate}{FullViewportUpdate}, to + ensure QGraphicsView doesn't spend time figuring out precisely what needs + to be redrawn. This application is very simple - if anything changes, + everything is updated. + \li It enables background caching - this makes no performance difference + with OpenGL, but without OpenGL it avoids unnecessary re-scaling of the + background pixmap. + \li It sets render hints that increase rendering quality. + \li If OpenGL is supported, a QGLWidget viewport is assigned to the view. + \endlist + + Finally, we start the state engine. + + \snippet graphicsview/padnavigator/padnavigator.cpp 19 + + The \l{QGraphicsView::resizeEvent()}{resizeEvent()} implementation calls + the base implementation, and then calls QGraphicsView::fitInView() to scale + the scene so that it fits perfectly inside the view. + + By resizing the main application window, you can see this effect yourself. + The scene contents grow when you make the window larger, and shrink when + you make it smaller, while keeping the aspect ratio intact. + + \section1 The main() Function + + \snippet graphicsview/padnavigator/main.cpp 0 + + The \c main function creates the QApplication instance, uses + Q_INIT_RESOURCE to ensure our compiled-in resources aren't removed by the + linker, and then creates a 3x3 \c PadNavigator instance and shows it. + + Our flippable pad shows up with a suitable splash item once control returns + to the event loop. + + \section1 Performance Notes + + The example uses OpenGL if this is available, to achieve optimal + performance; otherwise perspective tranformations can be quite costly. + + Although this example does use QGraphicsProxyWidget to demonstrate + integration of Qt widget components integrated into Graphics View, using + QGraphicsProxyWidget comes with a performance penalty, and is therefore not + recommended for embedded development. + + This example uses extensive item caching to avoid rerendering of static + elements, at the expense of graphics memory. +*/ |