many a month later, my attempt to rotate a line results in a sparsely filled circle

wtfCircle.pde

int w = 300; // width
int l = 300; // length (inaptly named because h is already taken)
int h = w/2;
int k = l/2;
int r = 100;
int xx = -1*r;
int yy;
int cnum = 7;
color myColor = getColor(cnum);


void setup() {
  size(w, l); 
  background(0);
  smooth();
} 
void draw() {
  //circl(h,k,r); //h,k,r
  if (xx < r) {
    int xx0 = h-xx;
    int xx1 = h+xx;
    int yy0 = (int) pow((pow(r, 2) - pow((xx0-h), 2)), .5)+k;
    int yy1 = -1*((int) pow((pow(r, 2) - pow((xx1-h), 2)), .5))+k;
    drawLine(xx0, yy0, xx1, yy1);
    xx++;
  } else {
    xx = -1*r;
    cnum = (cnum+5)%17;
    myColor = getColor(cnum);
  }
}

/*
resources:
http://krazydad.com/tutorials/makecolors.php
*/
color getColor(int i) {
  int center = 128;
  int widthh = 205;
  double frequency = .3;
  int red   = (int)Math.ceil(Math.sin(frequency*i+0) * widthh + center);
  int green = (int)Math.ceil(Math.sin(frequency*i+2) * widthh + center);
  int blue  = (int)Math.ceil(Math.sin(frequency*i+4) * widthh + center);
  return color(red,green,blue);
}

void drawLine(int x0, int y0, int x1, int y1) {
  int start, end;
  loadPixels();
  int dx = x1-x0;
  int dy = y1-y0;
  float slope = float(dy)/dx;
  int incr = (slope > 0) ? 1 : -1;
  boolean steep = (abs(slope)>1);
  int error = 0;
  if (dx == 0) {
    start = Math.min(y0,y1);
    end = Math.max(y0,y1);
    for (int i = start; i < end; i++) {
      pixels[i*width+x0] = myColor;
    }
  } else if (!steep) {
    start = Math.min(x0,x1);
    end = Math.max(x0,x1);
    int y = (x0 == start) ? y0 : y1;
    for (int i = start; i < end; i++) {
      pixels[y*width+i] = myColor;
      error += abs(dy);
        if (error >= abs(dx)) {
          y+=incr;
          error-=abs(dx);
        }
    } 
  } else if (steep) {
    start = Math.min(y0,y1);
    end = Math.max(y0,y1);
    int x = (y0 == start) ? x0 : x1;
    for (int i = start; i < end; i++) {
      pixels[i*width+x] = myColor;
      error += abs(dx);
        if (error >= abs(dy)) {
          x+=incr;
          error-=abs(dy);
        }
    }
  }
  updatePixels();
}

void mousePressed() {
  noLoop();
}

void mouseReleased() {
  loop();
}

void circl(int h, int k, int r) {
  loadPixels();
  int y;
  for (int x = (h-r); x < (h+r); x++) {
    y = (int) pow((pow(r, 2) - pow((x-h), 2)), .5)+k;
    pixels[y*width+x] = myColor;
    y = -1*((int) pow((pow(r, 2) - pow((x-h), 2)), .5))+k;
    pixels[y*width+x] = myColor;  
  }
  updatePixels();
}