size(400, 200);

float numStrings = 50;
float gapX = width / numStrings;
float gapY = height / numStrings;

for (int k = 0; k < numStrings; k++) {
  stroke(255, 0, 0);
  line(0, k*gapY, k*gapX, height);
  
  stroke(0, 0, 255);
  line(k*gapX, 0, width, k*gapY);
}