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QML Advanced Tutorial 4 - Finishing Touches
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*******************************************
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Now we're going to do two things to liven up the game: animate the blocks and add a High Score system.
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We've also cleaned up the directory structure for our application files. We now have a lot of files, so all the
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JavaScript and QML files outside of ``samegame.qml`` have been moved into a new sub-directory named "content".
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In anticipation of the new block animations, ``Block.qml`` file is now renamed to ``BoomBlock.qml``.
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Animating block movement
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------------------------
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First we will animate the blocks so that they move in a fluid manner. QML has a number of methods for adding fluid
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movement, and in this case we're going to use the Behavior element to add a SpringAnimation.
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In ``BoomBlock.qml``, we apply a SpringAnimation behavior to the ``x`` and ``y`` properties so that the
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block will follow and animate its movement in a spring-like fashion towards the specified position (whose
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values will be set by ``samegame.js``).Here is the code added to ``BoomBlock.qml``:
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.. pysideinclude:: samegame/samegame4/content/BoomBlock.qml
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The ``spring`` and ``damping`` values can be changed to modify the spring-like effect of the animation.
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The ``enabled: spawned`` setting refers to the ``spawned`` value that is set from ``createBlock()`` in ``samegame.js``.
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This ensures the SpringAnimation on the ``x`` is only enabled after ``createBlock()`` has set the block to
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the correct position. Otherwise, the blocks will slide out of the corner (0,0) when a game begins, instead of falling
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from the top in rows. (Try commenting out ``enabled: spawned`` and see for yourself.)
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Animating block opacity changes
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-------------------------------
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Next, we will add a smooth exit animation. For this, we'll use a Behavior element, which allows us to specify
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a default animation when a property change occurs. In this case, when the ``opacity`` of a Block changes, we will
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animate the opacity value so that it gradually fades in and out, instead of abruptly changing between fully
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visible and invisible. To do this, we'll apply a Behavior on the ``opacity`` property of the ``Image``
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element in ``BoomBlock.qml``:
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.. pysideinclude:: samegame/samegame4/content/BoomBlock.qml
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Note the ``opacity: 0`` which means the block is transparent when it is first created. We could set the opacity
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in ``samegame.js`` when we create and destroy the blocks,
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but instead we'll use states, since this is useful for the next animation we're going to add.
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Initially, we add these States to the root element of ``BoomBlock.qml``:
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property bool dying: false
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State{ name: "AliveState"; when: spawned == true && dying == false
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PropertyChanges { target: img; opacity: 1 }
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State{ name: "DeathState"; when: dying == true
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PropertyChanges { target: img; opacity: 0 }
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Now blocks will automatically fade in, as we already set ``spawned`` to true when we implemented the block animations.
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To fade out, we set ``dying`` to true instead of setting opacity to 0 when a block is destroyed (in the ``floodFill()`` function).
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Adding particle effects
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-----------------------
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Finally, we'll add a cool-looking particle effect to the blocks when they are destroyed. To do this, we first add a Particles element in
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``BoomBlock.qml``, like so:
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.. pysideinclude:: samegame/samegame4/content/BoomBlock.qml
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To fully understand this you should read the Particles documentation, but it's important to note that ``emissionRate`` is set
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to zero so that particles are not emitted normally.
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Also, we extend the ``dying`` State, which creates a burst of particles by calling the ``burst()`` method on the particles element. The code for the states now look
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.. pysideinclude:: samegame/samegame4/content/BoomBlock.qml
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Now the game is beautifully animated, with subtle (or not-so-subtle) animations added for all of the
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player's actions. The end result is shown below, with a different set of images to demonstrate basic theming:
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.. figure:: declarative-adv-tutorial4.gif
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The theme change here is produced simply by replacing the block images. This can be done at runtime by changing the \l Image \c source property, so for a further challenge, you could add a button that toggles between themes with different images.
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Keeping a High Scores table
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===========================
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Another feature we might want to add to the game is a method of storing and retrieving high scores.
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To do this, we will show a dialog when the game is over to request the player's name and add it to a High Scores table.
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This requires a few changes to ``Dialog.qml``. In addition to a ``Text`` element, it now has a
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``TextInput`` child item for receiving keyboard text input:
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.. pysideinclude:: samegame/samegame4/content/Dialog.qml
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:prepend: Rectangle {
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We'll also add a ``showWithInput()`` function. The text input will only be visible if this function
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is called instead of ``show()``. When the dialog is closed, it emits a ``closed()`` signal, and
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other elements can retrieve the text entered by the user through an ``inputText`` property:
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.. pysideinclude:: samegame/samegame4/content/Dialog.qml
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:prepend: Rectangle {
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Now the dialog can be used in ``samegame.qml``:
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.. pysideinclude:: samegame/samegame4/samegame.qml
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When the dialog emits the ``closed`` signal, we call the new ``saveHighScore()`` function in ``samegame.js``, which stores the high score locally in an SQL database and also send the score to an online database if possible.
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The ``nameInputDialog`` is activated in the ``victoryCheck()`` function in ``samegame.js``:
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.. pysideinclude:: samegame/samegame4/content/samegame.js
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:prepend: function vitoryCheck() {
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Storing high scores offline
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---------------------------
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Now we need to implement the functionality to actually save the High Scores table.
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Here is the ``saveHighScore()`` function in ``samegame.js``:
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.. pysideinclude:: samegame/samegame4/content/samegame.js
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First we call ``sendHighScore()`` (explained in the section below) if it is possible to send the high scores to an online database.
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Then, we use the Offline Storage API to maintain a persistant SQL database unique to this application. We create an offline storage database for the high scores using ``openDatabase()`` and prepare the data and SQL query that we want to use to save it. The offline storage API uses SQL queries for data manipulation and retrival, and in the ``db.transaction()`` call we use three SQL queries to initialize the database (if necessary), and then add to and retrieve high scores. To use the returned data, we turn it into a string with one line per row returned, and show a dialog containing that string.
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This is one way of storing and displaying high scores locally, but certainly not the only way. A more complex alternative would be to create a high score dialog component, and pass it the results for processing and display (instead of reusing the ``Dialog``). This would allow a more themeable dialog that could beter present the high scores. If your QML is the UI for a Python application, you could also have passed the score to a Python function to store it locally in a variety of ways, including a simple format without SQL or in another SQL database.
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Storing high scores online
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--------------------------
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You've seen how you can store high scores locally, but it is also easy to integrate a web-enabled high score storage into your QML application. The implementation we've done here is very
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simple: the high score data is posted to a php script running on a server somewhere, and that server then stores it and
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displays it to visitors. You could also request an XML or QML file from that same server, which contains and displays the scores,
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but that's beyond the scope of this tutorial. The php script we use here is available in the ``examples`` directory.
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If the player entered their name we can send the data to the web service us
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If the player enters a name, we send the data to the service using this code in ``samegame.js``:
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.. pysideinclude:: samegame/samegame4/content/samegame.js
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The XMLHttpRequest in this code is the same as the ``XMLHttpRequest()`` as you'll find in standard browser JavaScript, and can be used in the same way to dynamically get XML
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or QML from the web service to display the high scores. We don't worry about the response in this case - we just post the high
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score data to the web server. If it had returned a QML file (or a URL to a QML file) you could instantiate it in much the same
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way as you did with the blocks.
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An alternate way to access and submit web-based data would be to use QML elements designed for this purpose. XmlListModel
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makes it very easy to fetch and display XML based data such as RSS in a QML application (see the Flickr demo for an example).
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By following this tutorial you've seen how you can write a fully functional application in QML:
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* Build your application with QML elements.
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* Add application logic with JavaScript code.
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* Add animations with Behaviors and states.
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* Store persistent application data using, for example, the Offline Storage API or XMLHttpRequest.
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There is so much more to learn about QML that we haven't been able to cover in this tutorial. Check out all the
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demos and examples and the documentation to see all the things you can do with QML!
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[Previous :ref:`samegame3`]
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