Creating patterns: How can I create a geometric shape that looks like a rectangle with inward-curved circular arcs replacing the corners?

[svan]

Is there a way to display inverted rounded corners?

Have you tried using 4 arcs?

int _wndW = 600;
int _wndH = 600;

void drawArc(float x, float y, float radius, int rotation, float penSize) {
  float angle = 0.0;

  pushMatrix();
  translate(x, y);
  rotate(radians(rotation));
  for ( int i = 0; i < 90; i++ ) {
    angle = radians( i );
    x = cos( angle ) * radius;
    y = sin( angle ) * radius;
    fill(0);
    circle(x, y, penSize); // pen is circle
  }
  popMatrix();
}

void setup() {
  size(_wndW, _wndH);
  background(209);
  drawArc(130, 260, 135, -45, 6);
  drawArc(320, 70, 135, 45, 6);
  drawArc(510, 260, 135, 135, 6);
  drawArc(320, 450, 135, 225, 6);
}

void draw() {
}

Output: