Qt 4.8: QML Advanced Tutorial 1 - Creating the Game Canvas and Blocks

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QML Advanced Tutorial QML Advanced Tutorial 2 - Populating the Game Canvas

# QML Advanced Tutorial 1 - Creating the Game Canvas and Blocks

Files:

- declarative/tutorials/samegame/samegame1/Block.qml
- declarative/tutorials/samegame/samegame1/Button.qml
- declarative/tutorials/samegame/samegame1/samegame.qml
- declarative/tutorials/samegame/samegame1/samegame1.qmlproject

### Creating the application screen

The first step is to create the basic QML items in your application.

To begin with, we create our Same Game application with a main screen like this:

This is defined by the main application file, `samegame.qml`, which looks like this:

     import QtQuick 1.0

     Rectangle {
         id: screen

         width: 490; height: 720

         SystemPalette { id: activePalette }

         Item {
             width: parent.width
             anchors { top: parent.top; bottom: toolBar.top }

             Image {
                 id: background
                 anchors.fill: parent
                 source: "../shared/pics/background.jpg"
                 fillMode: Image.PreserveAspectCrop
             }
         }

         Rectangle {
             id: toolBar
             width: parent.width; height: 30
             color: activePalette.window
             anchors.bottom: screen.bottom

             Button {
                 anchors { left: parent.left; verticalCenter: parent.verticalCenter }
                 text: "New Game"
                 onClicked: console.log("This doesn't do anything yet...")
             }

             Text {
                 id: score
                 anchors { right: parent.right; verticalCenter: parent.verticalCenter }
                 text: "Score: Who knows?"
             }
         }
     }

This gives you a basic game window that includes the main canvas for the blocks, a "New Game" button and a score display.

One item you may not recognize here is the SystemPalette item. This provides access to the Qt system palette and is used to give the button a more native look-and-feel.

Notice the anchors for the `Item`, `Button` and `Text` elements are set using group notation for readability.

### Adding `Button` and `Block` components

The `Button` item in the code above is defined in a separate component file named `Button.qml`. To create a functional button, we use the QML elements Text and MouseArea inside a Rectangle. Here is the `Button.qml` code:

     import QtQuick 1.0

     Rectangle {
         id: container

         property string text: "Button"

         signal clicked

         width: buttonLabel.width + 20; height: buttonLabel.height + 5
         border { width: 1; color: Qt.darker(activePalette.button) }
         smooth: true
         radius: 8

         // color the button with a gradient
         gradient: Gradient {
             GradientStop {
                 position: 0.0
                 color: {
                     if (mouseArea.pressed)
                         return activePalette.dark
                     else
                         return activePalette.light
                 }
             }
             GradientStop { position: 1.0; color: activePalette.button }
         }

         MouseArea {
             id: mouseArea
             anchors.fill: parent
             onClicked: container.clicked();
         }

         Text {
             id: buttonLabel
             anchors.centerIn: container
             color: activePalette.buttonText
             text: container.text
         }
     }

This essentially defines a rectangle that contains text and can be clicked. The MouseArea has an `onClicked()` handler that is implemented to emit the `clicked()` signal of the `container` when the area is clicked.

In Same Game, the screen is filled with small blocks when the game begins. Each block is just an item that contains an image. The block code is defined in a separate `Block.qml` file:

     import QtQuick 1.0

     Item {
         id: block

         Image {
             id: img
             anchors.fill: parent
             source: "../shared/pics/redStone.png"
         }
     }

At the moment, the block doesn't do anything; it is just an image. As the tutorial progresses we will animate and give behaviors to the blocks. We have not added any code yet to create the blocks; we will do this in the next chapter.

We have set the image to be the size of its parent Item using `anchors.fill: parent`. This means that when we dynamically create and resize the block items later on in the tutorial, the image will be scaled automatically to the correct size.

Notice the relative path for the Image element's `source` property. This path is relative to the location of the file that contains the Image element. Alternatively, you could set the Image source to an absolute file path or a URL that contains an image.

You should be familiar with the code so far. We have just created some basic elements to get started. Next, we will populate the game canvas with some blocks.

QML Advanced Tutorial QML Advanced Tutorial 2 - Populating the Game Canvas