13 static void store_xy(
int x, 
int y)
 
   21 static void draw_line(
int x1, 
int y1, 
int x2, 
int y2)
 
   23     int x, 
y, x_end, y_end;
 
   24     int xinc, yinc, 
error;
 
   32     if (x == x_end && y == y_end) {
 
   55     if (delta_x > delta_y) {
 
   58         delta_y = delta_y * 2;
 
   59         error = delta_y - delta_x;
 
   60         delta_x = delta_y - (delta_x * 2);
 
   79         delta_x = delta_x * 2;
 
   80         error = delta_x - delta_y;
 
   81         delta_y = delta_x - (delta_y * 2);
 
  107         draw_line(x1, y1, x2, y2);
 
  116         int k = i - linewidth / 2;
 
  119             draw_line(x1 + k, y1, x2 + k, y2);
 
  121             draw_line(x1, y1 + k, x2, y2 + k);
 
def error
Display an error message using g.message -e 
void PNG_draw_line(int x1, int y1, int x2, int y2)