States

In previous chapters, we have implemented most of our game logic and added many new components. In this chapter we will see how to use the states concept in Qt Quick to define every major event, that requires e.g. camera adjustment, or changes important parameters.

Let’s summarize, once again, the game flow. Once the application is started, a game menu is shown and the player has two options: View the highscore table or start the game. When starting the game, the camera has to move to the back of the hamburger* and the keyboard controls will be enabled. The onion rings start to fly toward the player who has to try to hit them. After a certain number of onion rings, the boss enemy should appear. The final fight will take place from the birds eye view so the camera has to be moved first. Once the boss or player have been destroyed, a dialog appears to enable the player to enter his name with his score to store them in the highscore table.

We define the following states:

The Menu state: it’s the initial state where only the 3 buttons of the menu are shown.

The Highscore state: it’s an extension to the Menu state where the highscore table is also displayed.

The Enter Highscore state: Provides a textfield to enter the player’s name in the highscore table. The whole game scene will be frozen.

The Game state: Moves the camera behind the hamburger and starts the game. The keyboard controls are enabled and the game timer starts running.

The Boss Rotation state: Rotates the camera around the boss enemy then to a position above the scenery.

The Boss Fight state: Adjusts the x-bound after the camera has moved to a different point and starts the fight against the boss enemy.

//game.qml
...
state: "Menu"

states:[
    State{
        name: "Menu"
        PropertyChanges {target: player; ax: 0; ay: 0; vx: 0; vy:0;
                          position: Qt.vector3d(0, 0, 0); restoreEntryValues: false}
        PropertyChanges {target: root; score: 0; targetCount:0;
                          restoreEntryValues: false}
        PropertyChanges {target: cam; center: Qt.vector3d(0, 0, 0) }

    },
    State{
        name: "Highscore"
        extend: "Menu"
    },
    State{
        name: "EnterHighscore"
    },
    State{
        name: "Game"
        PropertyChanges {target: player; position: Qt.vector3d(0, 0, 0) }
    },
    State{
        name: "BossFight"
    PropertyChanges {target: player; ay: 0; vy:0;
      position: Qt.vector3d(0, 0, 0); restoreEntryValues: false}
    },
    State{
        name: "BossRotation"
        PropertyChanges {target: player; position: Qt.vector3d(0, 0, 0) }
    }
]
...

Note

We will cover the implementation of the game menu and the highscore dialog in the next chapter.

The targetTimer and gameTimer should not start until either Game or BossFight state are reached:

//Gamelogic.qml
...
id: targetTimer
running: root.state=="Game"
...
id: gameTimer;
running: root.state=="Game"||root.state=="BossFight"
...

Also, The player will not be able to move on the y axis during the fight against the boss enemy and shooting lasers obviously must only be possible when there is a target to shoot. Later, we will be implementing a fireLaser function.

//Gamelogic.qml
...
if(event.key == Qt.Key_W && root.state == "Game")
   upPressed = true
if(event.key == Qt.Key_S && root.state == "Game")
   downPressed = true
if(event.key == Qt.Key_Space && root.state == "BossFight")
   fireLaser();
...

Note

Note that the default state of our game is Menu. As we didn’t yet implement the game menu, at this stage of the implementation the user can not start the game as it’s supposed to be.

What’s Next?

Next we will implement the main menu for our game.