Variable Jump Height - objective-c

Question

I have been having great difficulty creating a jumping system whereby the user can tap the jump button for a small jump and hold it down for a higher jump.
I stumbled upon this topic:
https://gamedev.stackexchange.com/questions/13277/variable-height-jumping-in-side-scrollers
Which greatly helped me develop the following code:
PlayerMovementTimer = [NSTimer scheduledTimerWithTimeInterval:0.005 target:self selector:#selector(movePlayer) userInfo:nil repeats:YES];
[JumpButton addTarget:self action:#selector(jumpPlayer:) forControlEvents:UIControlEventTouchDown];
[JumpButton addTarget:self action:#selector(stopJump:) forControlEvents:UIControlEventTouchCancel | UIControlEventTouchUpInside | UIControlEventTouchDragExit];
- (void)movePlayer
{
CGFloat playerY = Player.center.y + PlayerYV;
if(playerY > 264) {
PlayerYV = 0;
playerY = 264;
}
if(playerY < 264) {
PlayerYV += 0.048f - PlayerYD;
}
if(HoldingJump && PlayerYV < 0 && PlayerYD + 0.0018f < 0.048f) {
PlayerYD += 0.0018f;
}
Player.center = CGPointMake(Player.center.x + PlayerXV, playerY);
}
- (IBAction)jumpPlayer:(id)sender
{
if(Player.center.y == 264) {
PlayerYD = 0;
PlayerYV = -2.25;
HoldingJump = true;
}
}
- (IBAction)stopJump:(id)sender
{
HoldingJump = false;
}
The code seems to work (some of the values need a bit of fine tuning but I haven't gotten round to that yet). The only problem is that the movement appears to be slightly jerky (even on the real device) and that when the player is at the top of the jump they accelerate really slowly and no values I put seem to be able to get the jump to look smooth like on Mario games.
Please take a look at the code and see if I am missing something obvious, or if there is a more efficient method of controlling movement than an NSTimer calling a void function. Also, is setting a UIImageView's position to a float value bad?
Thanks.

Answer 1

So there are quite a few things wrong here. First, yes, you should never be setting the origin of an ImageView or any other UI element to a coordinate position that is a fractional pixel. This causes sub-pixelling which will blur your image. To avoid this, all CGFloats should be rounded to the nearest whole number using roundf() or other similar rounding functions.
Another issue I can see is that you're setting Player.center. I hope for your sake that Player is not an ImageView cause you're going to be making your life harder. As mentioned above, when the origin of a frame is not set to a CGFloat that is a round number, you'll get sub-pixelling. When you use the center property, you can easily cause yourself to get on a bad origin value. For example, if I have a 11 by 11 image and set it's center to (11,11), the origin will get set to (5.5,5.5) and will cause sub-pixelling. Easy ways to avoid this is just do the math to place the origin correctly and make sure to round the CGFloats that you feed into it (or use CGRectIntegral on the frame before you set it).
A third issue here is that the timer is being called 0.005 seconds. Let's assume you want this game to run with 60 FPS. 60 FPS translates to about 0.0167 seconds. The timer is calling the method three times more often then it would need to even if you wanted 60 FPS and additionally, calling this method so often could be causing some of your jerky motion.
Now in terms of getting a "Mario" like jump, what you really need to do is look at getting a dedicated physics engine since if you're using the code above, you don't appear to have one. What a physics engine would do is it would apply a constant "gravity" which will help make the player jumps look and act more realistically. You would, when a player presses a button, apply an impulse up on the player character. The use of impulses would also simplify your work as you could apply impulses in different ways depending on how long they hold the button, etc. The code above is simply trying to get around this problem instead of addressing the real issue of you not having a physics engine.
Go investigate cocos2D and Box2D as a possible physics engine you could use. There are a wealth of resources on cocos2D+Box2D and there is a developer who even has made a tutorial on using cocos2D to create a Super Mario clone that should give you some basic understanding of how physics engines work: http://www.raywenderlich.com/15230/how-to-make-a-platform-game-like-super-mario-brothers-part-1