Hi

More like the first one

The bezier curve should never go outside the ellipse (ball). The start and end point is in the center left and right side of the ellipse.

 

Like an eye-lid?

Have a look at constrain() and map().

 

 

The real problem is how to calculate the controller points so I get a nice curve that intersects the mouse pointer when it's inside the ellipse.

See the images below where as I have programmed It now the curve will not intersect the mouse cursor. The mouse cursor is showed as a small ellipse with a point in.

map:

let's say that your circle has radius 100

and let's say that you have to drag the mouse outside the circle by 40 pixels for the the curve to match the circle's edge

 

that means that you know that when the cursor is 0 pixels away from the centre, the line is straight

and that when it's 90 pixels away from the centre, the curve matches the circle's edge

 

so you can map the cursor values

0 -> 0

and

90 -> 50

 

the constrain function works like following:

you could constrain mouseX for example:

if you'D write

x = constrain(mouseX,0,50); 

x would be the same as mouseX as long as its inbetween 0 and 50. as soon as mouseX is greater than 50, x just stays 50.

(example: mouseX = 23 -> x = 23 ; mouseX = 67 -> x = 50) same thing would happen if mouseX would be below zero

so you would have x staying in a range that you know. you could then map the values to something usefull for you, using tha map(); function.

if you write:

mappedX = map(x,0,50,0,1)

values from 0 to 50 are mapped onto values from 0 to 1

this could be something like what you wanted. you would have to figure out something better for the mapping, or try to build your bezierson the base of that code.

Ok I tried to make something like you proposed and it solved my problem when I move the cursor vertical and horizontal but in between there still are a problem... I need to make some compensation depending on which angle the mouse cursor are relative center of the ellipse.