The code below is from the book Beginning iPhone 3 Development, chapter 15, using the accelerometer to control a ball.
I want to use a label instead of the ball, and only move in the x direction.
However, I donno how to revise the code to achieve this goal.
Can anyone please help me?
THX so much!!!!
(id)initWithCoder:(NSCoder *)coder {
if (self = [super initWithCoder:coder]) {
self.image = [UIImage imageNamed:@"ball.png"];
self.currentPoint = CGPointMake((self.bounds.size.width / 2.0f) +
(image.size.width / 2.0f),
(self.bounds.size.height / 2.0f) + (image.size.height / 2.0f));
ballXVelocity = 0.0f;
ballYVelocity = 0.0f;
}
return self;
}
(id)initWithFrame:(CGRect)frame {
if (self = [super initWithFrame:frame]) {
// Initialization code
}
return self;
}
(void)drawRect:(CGRect)rect {
// Drawing code
[image drawAtPoint:currentPoint];
}
(void)dealloc {
[image release];
[acceleration release];
[super dealloc];
}
//#pragma mark -
- (CGPoint)currentPoint {
return currentPoint;
}
- (void)setCurrentPoint:(CGPoint)newPoint {
previousPoint = currentPoint;
currentPoint = newPoint;
if (currentPoint.x < 0) {
currentPoint.x = 0;
//ballXVelocity = 0;
ballXVelocity = - (ballXVelocity / 2.0);
}
if (currentPoint.y < 0){
currentPoint.y = 0;
//ballYVelocity = 0;
ballYVelocity = - (ballYVelocity / 2.0);
}
if (currentPoint.x > self.bounds.size.width - image.size.width) {
currentPoint.x = self.bounds.size.width - image.size.width;
//ballXVelocity = 0;
ballXVelocity = - (ballXVelocity / 2.0);
}
if (currentPoint.y > self.bounds.size.height - image.size.height) {
currentPoint.y = self.bounds.size.height - image.size.height;
//ballYVelocity = 0;
ballYVelocity = - (ballYVelocity / 2.0);
}
CGRect currentImageRect = CGRectMake(currentPoint.x, currentPoint.y,
currentPoint.x + image.size.width,
currentPoint.y + image.size.height);
CGRect previousImageRect = CGRectMake(previousPoint.x, previousPoint.y,
previousPoint.x + image.size.width,
currentPoint.y + image.size.width);
[self setNeedsDisplayInRect:CGRectUnion(currentImageRect,
previousImageRect)];
}
(void)draw {
static NSDate *lastDrawTime;
if (lastDrawTime != nil) {
NSTimeInterval secondsSinceLastDraw =
-([lastDrawTime timeIntervalSinceNow]);
ballYVelocity = ballYVelocity + -(acceleration.y *
secondsSinceLastDraw);
ballXVelocity = ballXVelocity + acceleration.x *
secondsSinceLastDraw;
CGFloat xAcceleration = secondsSinceLastDraw * ballXVelocity * 500;
CGFloat yAcceleration = secondsSinceLastDraw * ballYVelocity * 500;
self.currentPoint = CGPointMake(self.currentPoint.x + xAcceleration,
self.currentPoint.y +yAcceleration);
}
// Update last time with current time
[lastDrawTime release];
lastDrawTime = [[NSDate alloc] init];
}
