Character (sprite) animation

Question

What is the best way to handle character animation on the iPhone.
Is using the UIImageView method the best to handle simple sprite animation using a number of PNG's.
Is there a limit to the number of PNG images you should use?
Also what is the best way to handle simple effects like zoom and pan, on a block of animation?
Can a block of animation follow a curved path. e.g. a character walk cycle moving over a hill.
I appreciate any response. I have a background in 2D animation and need some direction to how best to create animations on the iPhone and also what limitations I am up against.
Thanks, Steve

Answer 1

Okay, that is something different. I misunderstood what you meant by 'animation'.
Moving 2D sprites in a game is done by creating a virtual model of the game world in the code that represents game objects by their positions in 2D space and their "movement" as a numerical velocity vector that specifies the number of pixels that the object should move per unit time. Time is simulated by updating the objects' position and redrawing the screen at some fixed time interval (the frame rate) determined by a timer.
Here is a simple ball animation sample that assumes you have a 48x48 pixel image named ball.png. It creates a UIView subclass that should be loaded by the AppDelegate class.
The header:
#import <UIKit/UIKit.h>
typedef struct
CGFloat x;
CGFloat y;
} Vector2D;
typedef struct
Vector2D position;
Vector2D velocity;
} Sprite;
@interface GameWorld : UIView {
Sprite ball;
UIImageView *ballImage;
@end
and the implementation:
#import "GameWorld.h"
#define kDotRadius 24
@implementation GameWorld
- (id)initWithFrame:(CGRect)frame {
if (self = [super initWithFrame:frame]) {
[UIApplication sharedApplication].statusBarHidden = YES;
ball.position.x = 200.0;
ball.position.y = 300.0;
ball.velocity.x = 3.0;
ball.velocity.y = -3.0;
ballImage = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"ball.png"]];
[self addSubview:ballImage];
[NSTimer scheduledTimerWithTimeInterval:(1.0 /30.0) target:self selector:@selector(update) userInfo:nil repeats:YES];
return self;
-(void)update {
if(ball.position.x - kDotRadius <= self.bounds.origin.x || ball.position.x + kDotRadius >= self.bounds.size.width)
ball.velocity.x *= -1.0; //negate to reverse direction
if(ball.position.y -kDotRadius <= self.bounds.origin.y || ball.position.y + kDotRadius >= self.bounds.size.height)
ball.velocity.y *= -1.0;
//commit to changes
ball.position.x += ball.velocity.x;
ball.position.y += ball.velocity.y;
[self setNeedsDisplay];//refresh the view
- (void)drawRect:(CGRect)rect {
ballImage.center = CGPointMake(ball.position.x, ball.position.y);
- (void)dealloc {
[super dealloc];
@end
So it is the UIImageView's center property that is used to create the movement of the image view across the screen. This could be done directly, but the use of C structs (Vector2D and Sprite) make the code easier to read. The center property is updated only at the moment when the screen redraw occurs.