controlling three steppers through mouse-position over serial communication


i am building a xy-plotter, where the x-axis is controlled by 2 steppers and the y-axis is controlled by one stepper.
it works fine with fixed values in arduino, but i’m struggling with controlling the steppers through the mouse-position in processing.

maybe someone could have a look at my code and help.
thanks in advance!

MultiStepper_Positions_Neu.ino (2.63 KB)

If the Arduino code works when reading data from the Serial Monitor application, but not when reading data from the Processing application, why would you assume that the problem is with the Arduino code?