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diff --git a/doc/src/declarative/qml-intro.qdoc b/doc/src/declarative/qml-intro.qdoc deleted file mode 100644 index 3f3e0e4..0000000 --- a/doc/src/declarative/qml-intro.qdoc +++ /dev/null @@ -1,616 +0,0 @@ -/**************************************************************************** -** -** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies). -** All rights reserved. -** Contact: Nokia Corporation (qt-info@nokia.com) -** -** This file is part of the documentation of the Qt Toolkit. -** -** $QT_BEGIN_LICENSE:FDL$ -** No Commercial Usage -** This file contains pre-release code and may not be distributed. -** You may use this file in accordance with the terms and conditions -** contained in the Technology Preview License Agreement accompanying -** this package. -** -** 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. -** -** If you have questions regarding the use of this file, please contact -** Nokia at qt-info@nokia.com. -** $QT_END_LICENSE$ -** -****************************************************************************/ - - - -/*! -\page qml-intro.html -\title Intro to Qt Quick - -\section1 Overview - -QML is a high level, scripted language. Its commands, more correctly \e elements, -leverage the power and efficiency of the Qt libraries to make easy to use -commands that perform intuitive functions. Draw a rectangle, display an image at -a position and so on. Behind these elements are complex C++ libraries that -efficiently perform the action. As with any graphical application, always -consider that this ability to easily build graphically rich applications means -that some care may be needed to prevent performance problems. - -The language also allows more flexibility of these commands by using -Javascript rather than C++ to add new layers of logic to your application. -Javascript is easier to learn than C++ and can be embedded into the QML -files or imported from a separate file. - -\bold{In QML the types of various 'objects' are referred to as \l {QML -Elements}{elements}}. - -An element usually has various \e properties that help define the element. For -example, if we created an element called Circle then the radius of the circle -would be a property. - - -\section1 A First Look - -The basic syntax of an \l{QML Elements}{element} is - -\qml -SomeElement { - id: myObject - // ... some other things here ... -} -\endqml - -Here we are defining a new object. We specify its 'type' first as SomeElement. -Then within matching braces { ... } we specify the various parts of our -element. - -The \c id is a unique identifier for the element, it must start with a lower -case letter and only contain letters, numbers and underscores. It is this -particular object's name. If this SomeElement \l {QML Elements}{element} was -a Rectangle instead and it was one of many then the \e optional unique id -would allow us to manipulate each element individually. - -Each visual element is ultimately based on, or inherits from, an element -called \l Item. \l Item has certain properties and actions that may be -useful. The properties have default values so you need only specify the -ones you will need. - -Take a simple element such as a \l Rectangle. It has an \c id, we will call -it \e myRectangle, it has a \c width and a \c height. Imagine that we -want a rectangle that is 500 pixels by 400 pixels in the x and y directions -(horizontal by vertical). - -We can implement this \l Rectangle with these properties this way - -\snippet doc/src/snippets/declarative/qml-intro/rectangle.qml document - -This is a valid QML script. To run it, copy it and save it to a file, say -myexample.qml, and on the command line run the following command: - -\code -qmlviewer myexample.qml -\endcode - -On Mac OS X, open the "QMLViewer" application instead and open the -\c myexample.qml file, or run it from the command line: - -\code -QMLViewer.app/Contents/MacOS/QMLViewer myexample.qml -\endcode - -It will create a very boring rectangle in its own window. - - -\section1 Hello World! - -We can now add some color and text to make a Hello World QML program. - -\l Rectangle has the property \l{Rectangle::color}{color} to produce a -background color. - -Text is handled by a different element called \l Text. We need to create a -\l Text object inside the \l Rectangle and set its \l{Text::}{text} -property to "Hello World!". So to set the text to "Hello world" and the -background colour to light gray, - -\snippet doc/src/snippets/declarative/qml-intro/hello-world1.qml document - - -\section1 Hello World Again - -From now on we will not always show the import statement for Qt but it -should still be there when you create your QML scripts. - -To make our Hello World example a little nicer set the position of the text -to be at pixel position x = 100, y = 100 within the displayed window. This -position belongs to the \l Text element so we set the position inside its -definition. Note that we separate different QML statements on the same line -with a semi-colon, or we could have simply put each statement on a new line - -\snippet doc/src/snippets/declarative/qml-intro/hello-world2.qml updated text - -Not only did we reposition the text, but the text was altered by adding -HTML tags to change the font size. The text color was also changed from the -default black to dark green by using a standard string for the color's SVG -name. - -We could also have used a hexadecimal string for the RGB (red-green-blue, as -#rrggbb) values of the color similar to the method used in HTML. For -example, mostly blue with a green tint, - -\snippet doc/src/snippets/declarative/qml-intro/hello-world3.qml updated text - -All of these changes occurred within the \l Text object which is the scope -of these property changes. - -Other objects may use the information but it belongs to the element where -the property has been defined. - - -\section1 Images - -To add an image to our little application we use the \l Image element. An -\l Image uses a path to an image file, and has properties to control -the aspect ratio, the image size, to tile the area amongst others. The -source of the image, the path to the file, is a URL. Therefore the file can -be local: \e {mydir/myimage1.png}. Or it can be remote: -\e {"http://www.example.com/images/myimage1.png"}. - -\snippet doc/src/snippets/declarative/qml-intro/hello-world4.qml added an image - -This displays the image, as we would expect, at the top left of the window. -The position of the default x = 0, y = 0 coordinate. The example here uses -a PNG file, but it could have been one of various supported formats, -including JPG and GIF. - -Let us reposition the image and enlarge it. Place it at the same 'x' offset -as the "Hello world again" text, but put it another 50 pixels below the -text, also make it 150 by 150 pixels in size, - -\snippet doc/src/snippets/declarative/qml-intro/hello-world5.qml positioning the image - -Adding the Hello World example, with the text and the image example we can -write a simple piece of QML that starts to look a bit better. - -\snippet doc/src/snippets/declarative/qml-intro/hello-world5.qml document - -The result is still quite simple - -\image qml-intro-helloa.png - - -\section1 Anchors: Aligning Elements - -Using absolute positioning, such as saying x = 100 and y = 150, works well -until the user or developer stretches or increases the size of the window. -Then the positions need to be recalculated. What would be nice would be a -relative means of positioning of objects in a window or rectangle. For -example, we want to place an image at the bottom of a rectangle, we would -like to specify the image's location as the 'bottom of the window', not a -specific coordinate. We can do this with the anchors property, which -objects inherit from Item. - -The anchors property is really a property group. It is a collection of -related properties. It has properties within it which can be used by means -of the dot notation. - -The dot notation uses object \c{id}s and property names to use a particular -object or property. Say I have a rectangle r1, which contains a rectangle -r2, which contains an Item item1, which has an 'x' property I want to -change. I just use the dot notation to identify it: r1.r2.item1.x - -If we want to position an image at the bottom of the rectangle it is -inside. I have to specify that the bottom of the image is also at the -bottom of the rectangle - -\snippet doc/src/snippets/declarative/qml-intro/anchors1.qml document - -This places the logo at the bottom left of the window. - -\image qml-intro-anchors1.png "A simple anchor" - -We would like it centered and not touching the bottom of the window, for -aesthetic reasons. For the centering we use the horizontalCenter property, -and to prevent the touching of the image to the bottom of the rectangle, -the bottomMargin property is used. So the new actions for the script are - - \list - \o set the bottom of the image (anchors.bottom) to be the bottom of the window - \o move the image to be in the horizontal center of the window - \o set a margin of 10 pixels so that the image does not touch the bottom window border - \endlist - -Encoded into QML the script becomes - -\snippet doc/src/snippets/declarative/qml-intro/anchors2.qml document - -Run this and resize the window. You will see that now the position of the -image adjusts during the resize. - -\image qml-intro-anchors2.png "Image Centered at the Bottom" - -You can also add another object say a block of descriptive text and place -it above or below the image or to the side. This code places some text just -above the image - -\snippet doc/src/snippets/declarative/qml-intro/anchors3.qml adding some text - -\image qml-intro-anchors3.png - -\note \e anchors is a property group, to be used within the object. When -referencing these properties from another object we use the property -directly, instead of saying: - -\qml -Item { - anchors.bottom: myRectangle.anchors.top // Wrong -} -\endqml - -we use - -\qml -Item { - anchors.bottom: myRectangle.top // Correct -} -\endqml - - -\section1 Transformations - -We can transform a graphical object to get additional effects. Rotate a -piece of text by 180 degrees to display upside-down text. Rotate an image -by 90 degrees to lay it on its side. These transformations require -additional information. - -For rotation, the additional information includes: the origin relative to -the object being rotated, the axis of rotation, and the angle in degrees to -rotate the image through in a clockwise direction. The axis does not have -to be the z-axis, the line between your eyes and the image, it could be -along the vertical y-axis or the horizontal x-axis. We have three -dimensions to play with. For simplicity in this example we will rotate -about the z-axis by 90 degrees in a negative direction, anti-clockwise. - -Rotation of text was also suggested. It could also be useful to scale the -text. We can do both. The \l {Item::transform}{transform} property is a -\e list of \l Transform elements, so using the list syntax -\c{myList: [ listElement1, listElement2, ... } ]} -we can produce a list of transformations. - -The text will be rotated by 45 degrees anti-clockwise and scaled -vertically by a factor of 1.5 and by 1.2 horizontally. - -Using the example above as the basis for this we have, - -\snippet doc/src/snippets/declarative/qml-intro/transformations1.qml document - -The code block in \c image1 starting with \c transform specifies that the -\l {Item::transform}{transform} property will be a Rotation through -90 -degrees, which is anti-clockwise, about the z-axis running through the -center of the image at (75,75), since the image is 150 x 150 pixels. - -The other transformation available is \l Translate. This produces a change -in position of the item. - -\note In a list of transformations the order of the transformations is -important. In the above example try swapping around the Scale transform with -the Rotation transform, remember to remove or add the comma. The results are -acceptable for our little test but not the same. - - -\section1 Animations - -Animation in QML is done by animating properties of objects. Properties -that are numbers, colors, Rectangles, points and directions. In QML these -are \l {QML Basic Types} named as real, int, color, rect, point, size, and -vector3d. There are a number of different ways to do animation. Here we -will look at a few of them. - -\section2 Number Animation - -Previously we have used a rotation transformation to change the orientation -of an image. We could easily animate this rotation so that instead of a -straight rotation counter-clockwise of 90 degrees we could rotate the image -through a full 360 degrees in an animation. The axis of rotation wont -change, the position of the center of the image will not change, only the -angle will change. Therefore, a NumberAnimation of a rotation's angle should -be enough for the task. If we wish for a simple rotation about the center -of the image then we can use the \c rotation property that is inherited -from \l Item. The rotation property is a real number that specifies the -angle in a clockwise direction for the rotation of the object. Here is the -code for our animated rotating image. - -\snippet doc/src/snippets/declarative/qml-intro/number-animation1.qml document - -The \c {transformOrigin: Item.Center} is redundant since this is the default -axis of rotation anyway. But if you change \c Center to \c BottomRight you -will see an interesting variation. - -Also if instead the \l Rotation transformation had been used then we would have -more control over the various parameters. We could vary the axis, to be not -just a different offset from the z-axis but along the y-axis, x-axis or -combination. For example, if the task had been to animate the rotation -about the y-axis passing through the center of the image then the following -code would do it. - -\snippet doc/src/snippets/declarative/qml-intro/number-animation2.qml document - -Here there is a rectangle 600 by 400 pixels. Placed within that rectangle -is an image 100 by 100 pixels. It is rotated about the center of the image -about the y-axis so that it looks as if it is rotating about an invisible -vertical string holding it up. The time it takes to complete the rotation is 3 -seconds (3,000 milliseconds). The NumberAnimation is applied to the angle -taking it from 0 (no change) to 360 degrees, back where it started. -Strictly speaking it isn't necessary to go from 0 to 360 since the same -location is duplicated, but it makes it easier to read in this example and -it has no visible effect on the animation. The number of loops that the -animation will execute is set to \c {Animation.Infinite} which means that the -animation is in an endless loop. - -To see an interesting variation. Change the axis to \c {axis { x:1; y:1; z:1 -}}. This is a line coming from the center of the image downwards to the -right and out of the screen. Although the change is simple the rotation -seems complex. - -\section2 Sequential Animation - -For a more complex animation we will need two images. The first image will -be placed at the center of a window (Rectangle) and the second image will -be at the upper left of the window. The animation will move the second -image from the top left of the window to the bottom right. In doing so we -will be animating the position and the size of the image. - -First create two images - -\snippet doc/src/snippets/declarative/qml-intro/sequential-animation1.qml document - -We will add to 'image1' a SequentialAnimation from x = 20 to the target of -x = 450. The 'from' values will be used because we will be repeating the -animation, so the object needs to know where the original position is, both -x and y. The SequentialAnimation of x will set it to repeat by indicating -that the number of animation loops is infinite, meaning that the 'loop' -counter will be set to a value Animation.Infinite that indicates an endless -cycle. Also there will be a NumberAnimation to vary the numeric property -between the x values and over a given duration. After the NumberAnimation -there will be a PauseAnimation that will pause the animation for 500 -milliseconds (half a second) simply for the visual effect. - -\snippet doc/src/snippets/declarative/qml-intro/sequential-animation2.qml adding a sequential animation - -A similar block of code is written for the animation of the 'y' value of -the position. - -We will also animate the scale of the object, so as it goes from top left -to bottom right of the window it will become smaller until about midway, -and then become larger. To complete the animation we will set the 'z' -values of the images. 'z' is the stacking order, the z-axis effectively -points out from the screen to your eyes with the default value of 'z' being -0. So if we set the Rectangle to have z with value zero, just to be sure, -and image1 to 1 and image2 to 2 then image2 will be in the foreground and -image1 in the background. When image1 passes image2 it will pass behind it. -The completed code looks like - -\snippet doc/src/snippets/declarative/qml-intro/sequential-animation3.qml document - -The \c {easing.type} has many options, expressed as a string. It specifies the -kind of equation that describes the acceleration of the property value, not -necessarily position, over time. - -For example, \e InOutQuad means that at the start and the end of the animation the -'velocity' is low but the acceleration or deceleration is high. Much like a car -accelerating from stop, and decelerating to stop at the end of a journey, -with the maximum speed being in the middle. Examine the \l {PropertyAnimation::easing.type} -{easing} documentation and the various graphs that show the effect. The horizontal -axis, 'progress', can be thought of as time. The vertical axis is the value -of the particular property. - -In discussing animation we need to describe three objects: State, MouseArea -and Signals. Although independent of the animation elements, animation -delivers some of the best examples that illustrate these new elements. - - - -\section2 Animation Summary - -\table - \header - \o Name - \o Description - \row - \o PropertyAnimation - \o a property value on a target object is varied to a specified value over a given time. - - \row - \o NumberAnimation - \o animate a numeric property from one value to another over a given time. - - \row - \o PauseAnimation - \o results in the task waiting for the specified duration, in milliseconds. - - \row - \o SequentialAnimation - \o allows us to list in order the animation events we want to occur, first A then B then C and so on. - - \row - \o ParallelAnimation - \o enables us to run different animations at the same time instead of sequentially. - -\endtable - - -\section1 Using States - -A state is a defined set of values in the configuration of an object and -often depends on the previous state. For example, a glass could be in a -state we call 'HalfFull' if it is being filled with a liquid and has -reached half of its total capacity. We could also have a state called -HalfEmpty which is the state that occurs when the amount of liquid drops to -half of the glass's capacity. Both states represent the same amount of -liquid, but we consider them different. Likewise, states in a program -represent not just values but may include how the current values were -reached. - -When a state changes a \e transition occurs. This is an opportunity to make -changes or take actions that depend on the movement to the new state. For -example, if we had a scene in the country where the state variable has two -states "daylight" and "night". Then when the state changes to "night" at -this transition the sky would be made dark, stars would be shown, the -countryside would be darkened. And when the state changes to "daylight" the -opposite changes would be made: the sky is now blue, the scenery is green, -there is a sun in the sky. - -Here is a simple QML program that shows the change of state in the above -example. We have two rectangles, the top one is the 'sky' and the bottom -one is the 'ground'. We will animate the change from daylight to night. -There will be two states, but we only need to define one since 'daylight' -will be the default state. We will just go to 'night' by clicking and -holding the left mouse button down, releasing the mouse button will reverse -the process - -\snippet doc/src/snippets/declarative/qml-intro/states1.qml document - -Several new things appear in this sample. Firstly, we use a \l MouseArea -element to detect mouse clicks in the \e mainRectangle. Secondly, we use -the list notation [ thing1 , thing2, ... ] to build a list of states and a -list of transitions. - -\l MouseArea defines a region that will respond to mouse clicks. In this case -we are only concerned with when the mouse is pressed or not pressed, not -the particular button or other details. The area of the MouseArea is the -entire main window, mainRectangle, so that clicking anywhere in this region -will start the animation. Since we are using the 'pressed' mouse state, -then the animation will move from 'daylight' to 'night' only while the mouse -button remains pressed. - -When the button is released the 'daylight' state is entered and the -transition from 'night' to 'daylight' is triggered causing the animation to -run. The transition specifies the duration in milliseconds of the -ColorAnimation, while the state specifies the color of the new state. - -The PropertyChanges command is the way that we nominate which properties -will change in a change of state, and what new value the property will -take. Since, for example, we want the 'sky' region to turn to dark blue and -the 'ground' region to turn to black for the 'night' state, then the -rectangles for those regions are the 'target' and the property in the target -is 'color'. - - -\section1 Signals - -Signals are simply events that can be hooked up to actions we want performed. -In QML they are usually preceded by the word 'on', for example in the animation -using a MouseArea the signal was \l {MouseArea::onPressed}{onPressed}. If -you look at the C++ documentation you will see a lot of talk about -\l {Signals & Slots}{Signals and Slots}. Signals are connected to Slots. The -signal represents an event and the Slot is the function that does something -based on that event. You can also have Signals connected to other Signals, so -that one Signal (event) triggers another Signal (event), and so forth. It is -nice to know this is what happens beneath the QML layer but not essential for -using QML. - -Most elements do not have Signals associated with them. However, a few like -the \l Audio element have many signals. Some of the \l Audio signals are -used to represent events such as when the audio is stopped, play is pressed, -paused, and reaching the end of the media. They allow the developer to connect, - for example, the press of a user interface button (perhaps a MouseArea) to - some QML that will handle this event. - - -\section1 Analyzing An Example: Dial Control - -In the Qt \e {examples/declarative/ui-components} folder you will find a folder -\e {dialcontrol} which contains the \e dialcontrol example. - -\image qml-dial.png "QML Dial example with Slider" - -In essence this small application has a sliding bar that you can slide using -a mouse, and a graphical dial that responds to the position of the slider. - -The code for the example is in two parts: Dial.qml and dialcontrol.qml. - -\e {Dial.qml} can be found in the \e content sub-directory. It defines a \c Dial -component similar to an odometer. Eventually, the example will hook up a slider -component so that moving the slider will change the position of a needle on the -dial. - -The code for the \c Dial, identified by the name of the file, contains four images -in overlapping order: the background (numbers and divisions), the shadow of the -needle, the needle itself, and finally the 'glass' overlay (containing -transparent layers). - -The \c needle_shadow.png image has a \l Rotation assigned to the \e transform -attribute of the \l Image. The rotation is set to match the angle of the needle -image angle value \e {needleRotation.angle}. Both the needle and the -needle_shadow have the same default \e x and \e y values but the rotation origin -for the needle is slightly different so that a shadow will be evident as the -needle moves. - -\snippet examples/declarative/ui-components/dialcontrol/content/Dial.qml needle_shadow - -And the needle - -\snippet examples/declarative/ui-components/dialcontrol/content/Dial.qml needle - -The final image is the overlay which simply has a position defined. - -\snippet examples/declarative/ui-components/dialcontrol/content/Dial.qml overlay - -\e {dialcontrol.qml} in the \e {examples/declarative/ui-components/dialcontrol} directory is the -main file of the example. It defines the visual environment that the Dial -will fit into. Because the \e Dial component and the images live in the \e -content sub-directory we will have to import this into \e dialcontrol.qml. So the -start of the file looks like - -\snippet examples/declarative/ui-components/dialcontrol/dialcontrol.qml imports - -The visual space is bound by a 300 by 300 pixel \l Rectangle which is given -a gray color. Inside this rectangle is our component \e Dial and a \l Rectangle. -Inside the rectangle called 'container' is another rectangle with the -interesting name 'slider'. - -\snippet examples/declarative/ui-components/dialcontrol/dialcontrol.qml 0 - -The Dial component, named 'dial, is \e anchored to the center of the main -rectangle. The \c value attribute of 'dial' is set to a value based on the -'slider' horizontal position and the 'container' width. So changes to the -'slider' position will change the Dial \c value which is used in Dial to compute -the rotation of the needle image. Notice this piece of code in Dial where -the change in \c value modifies the position of the needle. - -\snippet examples/declarative/ui-components/dialcontrol/content/Dial.qml needle angle - -This is part of the \c needleRotation that rotates the needle and causes the -rotation of its shadow. \l SpringAnimation is an element that modifies the value -of that rotation \e angle and mimics the oscillatory behavior of a spring, -with the appropriate \e spring constant to control the acceleration and the \e -damping to control how quickly the effect dies away. - -The 'container' is light gray with a color gradient defined using -\l GradientStop. The gradient is applied vertically. If you need a horizontal -gradient then you could apply the vertical gradient and then rotate the item -by 90 degrees. - -The 'slider' is dark gray and also has a vertical color gradient. The most -important thing about the 'slider' is that it has a MouseArea defined, which -specifies a \c {drag.target} on itself along the X-axis. With minimum -and maximum values on the X-axis defined. So we can click on the 'slider' and -drag it left and right within the confines of the 'container'. The motion of -the 'slider' will then change the \c value attribute in \e Dial as discussed -already. - -Also notice the use of a \c radius value for a rectangle. This produces rounded -corners. That is how the 'container' and 'slider' are displayed with a -pleasant rounded look. - - - -*/ - - - |