Strange behaviour with QPainter

[faldzip]

I still didn't understand why the static gave that behaviour if I update at every call the member variablke

Here is a small example:

void foo() {
  static int counter = 0;
  cout << "foo has been called " << ++counter << " times\n";
}
 
int main() {
  for( int i = 0; i < 10; ++i ) foo();
}

void foo() {
  static int counter = 0;
  cout << "foo has been called " << ++counter << " times\n";
}
 
int main() {
  for( int i = 0; i < 10; ++i ) foo();
}

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it will display:
foo has been called 1 times
foo has been called 2 times
foo has been called 3 times
...
foo has been called 10 times

So, as it can be easily noticed, this line:

static int counter = 0;

static int counter = 0;

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is called ONCE, when this line is rached for the first time. So counter variable is created once and 0 is assigned to it once. Then it remains in memory for every foo() call until the end of app execution.
So in your code point[3] was created and initialized once on the first call of paintEvent() and remained there forever (until program ends).