This is the fourth part of a series (that began here). So far, we have a game where you can whizz around the screen avoiding trees. This effectively encompasses most aspects of a game of this type; that is, you can move, and there is a something preventing you.
The next step is to introduce something for the player to try to do, and give a score based on that. In our case, our player is going to try and collect cups – as per the original game. The asset I’ve created for the cup is here. For anyone following this series, you may have noticed that my artwork is a little… crap.
The source for this post is here.
Cups
The first thing that we’ve done here is added some code to place a few cups around the screen; the code for this was essentially the same as build obstacles:
placeCups() {
let cups = [];
const cupCount = 1;
for (let i = 1; i <= cupCount; i++) {
const centreX = Math.floor(Math.random() * this.state.windowWidth) + 1;
const centreY = Math.floor(Math.random() * this.state.windowHeight) + 1;
cups.push(<GameItem key={i} image={cupImg} centreX={centreX} centreY={centreY} width={this.spriteWidth} height={this.spriteHeight} itemType={2} />);
}
return cups;
}
In a later post, I hope to do a full refactor, but for now, we have a separate function. This is rendered in the same way as the obstacles:
render() {
return <div onKeyDown={this.onKeyDown} tabIndex="0">
<GameStatus Lives={this.state.playerLives} Message={this.state.message} Score={this.state.score} />
<Background backgroundImage={backgroundImg}
windowWidth={this.state.windowWidth} windowHeight={this.state.windowHeight} />
<Car carImage={this.state.playerCrashed ? brokenCarImg : carImg}
centreX={this.state.playerX} centreY={this.state.playerY}
width={this.spriteWidth} height={this.spriteHeight}
rotation={this.state.playerRotation} />
{this.obstacles}
{this.cups}
</div>
}
Collecting cups
In order to collect something, the player must collide with it. We need to change the collision code slightly to make it a little more re-usable:
detectAnyCollision(rect1) {
// Have we crashed or left the screen
if (this.detectOutScreen(rect1)) {
return true;
}
let collided = this.detectGameItemCollision(this.halfWidth, this.halfHeight, rect1, this.obstacles);
if (collided !== undefined) {
return true;
}
return false;
}
detectGameItemCollision(halfWidth, halfHeight, rect1, gameItemList) {
const collided = gameItemList.find(a => {
var rect2 = {
x: a.props.centreX - halfWidth, y: a.props.centreY - halfHeight,
width: this.spriteWidth, height: this.spriteHeight
};
return (this.detectCollision(rect1, rect2));
});
return collided;
}
As you can see, we now have a function that returns the item that we collided with, rather than a simple boolean. We then use this at the end of the game loop to determine whether we collided with a cup:
// Check for collected cup
const item = this.detectGameItemCollision(this.halfWidth, this.halfHeight, rect1, this.cups);
if (item !== undefined) {
this.collectedCup(item.key);
}
Score
There’s little point in zooming around collecting cups, if there’s no permanent record, so we need to add a score. Let’s start with a state variable in game.jsx:
this.state = {
playerX: 100,
playerY: 100,
windowWidth: 1500,
windowHeight: 1500,
playerMomentum: 0,
playerRotation: 0,
playerVelocityX: 0,
playerVelocityY: 0,
playerLives: 3,
playerCrashed: false,
gameLoopActive: false,
message: "",
score: 0
};
And here’s the collectedCup function we mentioned a second ago:
collectedCup(key) {
this.setState({ score: this.state.score + 1 });
this.cups = this.cups.filter(cup => cup.key != key);
this.updateMessage("Collected cup");
}
All we’re doing here is simply updating the score and then removing that cup from the list.
The final part is to display the score on the screen; let’s have a look at our updated GameStatus.jsx:
function GameStatus(props) {
const flexStyle = {
display: 'flex',
position: 'absolute',
zIndex: 1,
margin: 20,
justifyContent: 'center',
alignItems: 'center',
width: '100%'
};
const labelStyle = {
zIndex: 1,
margin: 50
};
return (
<div className="flex-container" style={flexStyle}>
<label style={labelStyle}>
Lives Remaining: {props.Lives}
</label>
<label style={labelStyle}>
Score: {props.Score}
</label>
<label style={labelStyle}>
{props.Message}
</label>
</div>
);
}
As you can see, we’re just displaying the score as part of the status.
In the next post, we’ll have a look at the concept of levels, and introduce a time limit.
