QML Advanced Tutorial 4 - Finishing Touches¶
Adding some flair¶
In this chapter, you are going to do two things to enhance the game experience: animate the blocks and add a High Score system.
You should clean up the directory structure, now that there are a
lot of files. Move all the JavaScript and QML files outside of samegame.qml
into a new sub-directory named “content”.
In anticipation of the new block animations, Block.qml file is now renamed
to BoomBlock.qml.
Animating block movement¶
First, you will animate the blocks so that they move in a fluid manner. QML has
a number of methods for adding fluid movement, and in this case you are going to
use the Behavior type to add a SpringAnimation. In BoomBlock.qml, apply a
SpringAnimation behavior to the x and y properties so that the
block follows and animate its movement in a spring-like fashion towards the
specified position (whose values are set by samegame.js). Here is the code
added to BoomBlock.qml:
property bool spawned: false
Behavior on x {
enabled: spawned;
SpringAnimation{ spring: 2; damping: 0.2 }
}
Behavior on y {
SpringAnimation{ spring: 2; damping: 0.2 }
}
The spring and damping values can be changed to modify the spring-like
effect of the animation.
The enabled: spawned setting refers to the spawned value that comes from
the createBlock() function in samegame.js. This ensures that the
SpringAnimation on x is only enabled after createBlock() has set the
block to the correct position. Otherwise, the blocks will slide out of the
corner (0,0) when a game begins, instead of falling from the top in rows.
Try commenting out the line, enabled: spawned, and see the effect for
yourself.
Animating block opacity changes¶
Next, add a smooth exit animation. For this, use a Behavior type, which
allows us to specify a default animation when a property change occurs. In this
case, when the opacity of a Block changes, animate the opacity value so that
it gradually fades in and out, instead of abruptly changing between fully
visible and invisible. To do this, apply a Behavior on the opacity property
of the Image item in BoomBlock.qml:
Image {
id: img
anchors.fill: parent
source: {
if (type == 0)
return "../../shared/pics/redStone.png";
else if (type == 1)
return "../../shared/pics/blueStone.png";
else
return "../../shared/pics/greenStone.png";
}
opacity: 0
Behavior on opacity {
NumberAnimation { properties:"opacity"; duration: 200 }
}
}
Note the opacity: 0, which means the block is transparent when it is first
created. You could set the opacity in samegame.js when we create and
destroy the blocks, but use states instead, as this is useful for the next
animation you are going to add. Initially, add these States to the root
item of BoomBlock.qml:
property bool dying: false
states: [
State{ name: "AliveState"; when: spawned == true && dying == false
PropertyChanges { target: img; opacity: 1 }
},
State{ name: "DeathState"; when: dying == true
PropertyChanges { target: img; opacity: 0 }
}
]
Now blocks will automatically fade in, as spawned is set to true when
you implemented the block animations. To fade out, set dying to true
instead of setting opacity to 0 when a block is destroyed (in the
floodFill() function).
Adding particle effects¶
Finally, add a cool-looking particle effect to the blocks when they are
destroyed. To do this, first add a Particles item in
BoomBlock.qml, like this:
Particles {
id: particles
width: 1; height: 1
anchors.centerIn: parent
emissionRate: 0
lifeSpan: 700; lifeSpanDeviation: 600
angle: 0; angleDeviation: 360;
velocity: 100; velocityDeviation: 30
source: {
if (type == 0)
return "../../shared/pics/redStar.png";
else if (type == 1)
return "../../shared/pics/blueStar.png";
else
return "../../shared/pics/greenStar.png";
}
}
To fully understand this you should read the Particles documentation,
but it’s important to note that emissionRate is set to zero so that
particles are not emitted normally. Also, extend the dying State,
which creates a burst of particles by calling the burst() method on the
particles item. The code for the states now look like this:
states: [
State {
name: "AliveState"
when: spawned == true && dying == false
PropertyChanges { target: img; opacity: 1 }
},
State {
name: "DeathState"
when: dying == true
StateChangeScript { script: particles.burst(50); }
PropertyChanges { target: img; opacity: 0 }
StateChangeScript { script: block.destroy(1000); }
}
]
Now the gaming experience is pleasing with these animations. With a few more simple animations for all of the player’s actions, it will look even better. The end result is shown below, with a different set of images to demonstrate the basic theme:
The theme change here is produced simply by replacing the block images. This
can be done at runtime by changing the source property of the Image. You
could go a step further and add a button that toggles between themes with
different images.
Keeping a high scores table¶
Another feature you might want to add to the game is a method of storing and retrieving high scores.
To do this, show a dialog when the game is over to request the player’s name
and add it to a High Scores table. This requires a few changes to
Dialog.qml. In addition to a Text item, it now has a TextInput
child item for receiving keyboard text input:
Rectangle {
...
TextInput {
id: textInput
anchors { verticalCenter: parent.verticalCenter; left: dialogText.right }
width: 80
text: ""
onAccepted: container.hide() // close dialog when Enter is pressed
}
...
}
Also, add a showWithInput() function. The text input will only be visible if
this function is called instead of show(). When the dialog is closed, it
emits a closed() signal, and other items can retrieve the text entered by
the user through the inputText property:
Rectangle {
...
property string inputText: textInput.text
signal closed
function show(text) {
dialogText.text = text;
container.opacity = 1;
textInput.opacity = 0;
}
function showWithInput(text) {
show(text);
textInput.opacity = 1;
textInput.focus = true;
textInput.text = ""
}
function hide() {
textInput.focus = false;
container.opacity = 0;
container.closed();
}
...
}
Now the dialog can be used in samegame.qml:
Dialog {
id: nameInputDialog
anchors.centerIn: parent
z: 100
onClosed: {
if (nameInputDialog.inputText != "")
SameGame.saveHighScore(nameInputDialog.inputText);
}
}
When the dialog emits the closed signal, we call the new saveHighScore()
function in samegame.js, to store the high score locally in an SQL database
and also send the score to an online database if possible.
The nameInputDialog is activated in the victoryCheck() function in
samegame.js:
function vitoryCheck() {
...
//Check whether game has finished
if (deservesBonus || !(floodMoveCheck(0, maxRow - 1, -1))) {
gameDuration = new Date() - gameDuration;
nameInputDialog.showWithInput("You won! Please enter your name: ");
}
}
Storing high scores offline¶
Now, you need to implement the functionality to actually save the High Scores table.
Here is the saveHighScore() function in samegame.js:
function saveHighScore(name) {
if (scoresURL != "")
sendHighScore(name);
var db = openDatabaseSync("SameGameScores", "1.0", "Local SameGame High Scores", 100);
var dataStr = "INSERT INTO Scores VALUES(?, ?, ?, ?)";
var data = [name, gameCanvas.score, maxColumn + "x" + maxRow, Math.floor(gameDuration / 1000)];
db.transaction(function(tx) {
tx.executeSql('CREATE TABLE IF NOT EXISTS Scores(name TEXT, score NUMBER, gridSize TEXT, time NUMBER)');
tx.executeSql(dataStr, data);
var rs = tx.executeSql('SELECT * FROM Scores WHERE gridSize = "12x17" ORDER BY score desc LIMIT 10');
var r = "\nHIGH SCORES for a standard sized grid\n\n"
for (var i = 0; i < rs.rows.length; i++) {
r += (i + 1) + ". " + rs.rows.item(i).name + ' got ' + rs.rows.item(i).score + ' points in ' + rs.rows.item(i).time + ' seconds.\n';
}
dialog.show(r);
});
}
First, call sendHighScore() to send the high scores to an online database.
Then, use the Offline Storage API to maintain a persistent SQL database, unique
to this application. Create an offline storage database for the high scores
using openDatabase(), then 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
retrieval. The db.transaction() uses three SQL queries:
To initialize the database, if necessary.
To add high scores to the database.
To retrieve the high score records.
To use the returned records, turn it into a string with one line per row, and show a dialog containing that string.
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 allows for a more themeable dialog that could
present the high scores in a better way. If you are using QML-based UI for a
Python application, you can also pass the score to a function that stores it
locally in a variety of ways. This can be a simple format without SQL, or in
another SQL database.
Storing high scores online¶
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 application. The
implementation we’ve done here is very simple: the high score data is posted to
a php script running on a server somewhere, and that server then stores it and
displays it to visitors. You could also request an XML or QML file, which
contains and displays the scores, but that’s beyond the scope of this tutorial.
The php script used here is available in the examples directory.
If the player entered their name, you can send the data to an online database
service. The following code snippet from samegame.js demonstrates this well:
function sendHighScore(name) {
var postman = new XMLHttpRequest()
var postData = "name=" + name + "&score=" + gameCanvas.score + "&gridSize=" + maxColumn + "x" + maxRow + "&time=" + Math.floor(gameDuration / 1000);
postman.open("POST", scoresURL, true);
postman.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
postman.onreadystatechange = function() {
if (postman.readyState == postman.DONE) {
dialog.show("Your score has been uploaded.");
}
}
postman.send(postData);
}
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 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
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
way as you did with the blocks.
An alternate way to access and submit web-based data would be to use QML items designed for this purpose. XmlListModel 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).
That’s it!¶
By following this tutorial you’ve seen how you can write a fully functional application in QML:
Build your application with QML items.
Add application logic with JavaScript code.
Add animations with Behaviors and states.
Store persistent application data using, for example, the Offline Storage API or XMLHttpRequest.
There is so much more to learn about QML that we haven’t been able to cover in this tutorial. Check out all the demos and examples and the documentation to see all the things you can do with QML!
[Previous QML Advanced Tutorial 3 - Implementing the Game Logic]
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