How does CGPoint Variable work behind the scenes? - iphone

Question

I'm not sure how the CGPoint variable that I have created knows how to handle the specific if statement.
For example, I have CGPoint myVelocity; then I have an arbitrary number float maximumVelocity = 100;
Then I execute the following code
if (myVelocity.x > maximumVelocity) {
myVelocity.x = maximumVelocity;
}
else if (myVelocity.x < -maximumVelocity)
{
myVelocity.x = -maximumVelocity;
}
From what I understand, if the first condition is met, which is myVelocity.x > maximumVelocity then the CGPoint variable is set to the maximum, which is the number 100. This is so that my variable never exceeds the arbitrary number. And the other condition is set up so that it doesn't go into the negative..
At least that's what I think.
Now here is the important part of this post.. I'm confused with how the myVelocity variable knows what the that arbitrary number is. For example is it 10? is it 25 the next second or when does it reach 100.
I should also point out that before the if statement is run, I have the following code stored in myVelocity
The following is the code that is stored into 'myVelocity' prior to the if statement executing.
float deceleration = 0.4f;
float sensitivity = 6.0f;
float maximumVelocity = 100;
myVelocity.x = myVelocity.x *deceleration + acceleration.x *sensitivity;
I have recently inquired about code smilar to the latter part of my question, but now I'm curious about the former.

Answer 1

A CGPoint is just a struct with "x" and "y" components. You can think of it as an easier way to pass around a pair of floats.
So your code above would be equivalent to:
float x;
// other stuff
if (x > maximumVelocity) {
x = maximumVelocity;
}
else if (x < -maximumVelocity)
{
x = -maximumVelocity;
}
Now pair that with another variable by using a struct:
struct CGPoint {
float x;
float y;
};
and to access that "x" variable, to either set or read from it, use ".x", like you did in your code sample.
(P.S. CGPoints actually are a pair of CGFloats for reasons that are irrelevant to this post)

Answer 2

GCPoint represent a bidimensional space, ideally storing a velocity in a CGPoint means that you need a velocity vector represented by 2 dimensions, x and y.
In your case i see that you only use 1 dimension, i didnt quite get what your trying to achieve but in your case you can just use a float to store velocity value if it has not a direction.
If you need a 2 dimension velocity you have to check for maximumVelocity by checking the lenght of the vector. In you example your checking only the x dimension, but if the velocity is x=50,y=20000 this is moving pretty fast on the y axis.
ccpLength(<#const CGPoint v#> let you check the lenght of a CGPoint, so you can compare with a float to see if the actual velocity is faster than your maximum, in that case you need to normalize your vector to actually match your maxiumVelocity, you can do this with
ccpMult(v, maximumVelocity/ccpLength(v))