Date:    Fri, 21 Aug 1992 0:48:29 MST
From: CHAYS AT MRSVAX DOT MIS DOT ARIZONA DOT EDU (Tear it down ... there's got to be a better way)
Subject: some interesting performance notes for libgrx2.02 and djgpp1.08
To: djgpp AT sun DOT soe DOT clarkson DOT edu

/* circle2.c
 * coded in C on a hot day in Tucson AZ by Chris Hays from Michael Eisenburg's 
 * "Programming In Scheme" pc scheme implementation of circle2, 
 * originally by John E. Connet of the University of Minnisota
 *
 * Performance Note:
 *
 * This program took 25 minutes to run using a trident SVGA card
 * and 14 seconds (640x480) and 37 seconds (1024x768) using an
 * ATI Graphics Vantage with libgrx 2.02 and DJGPP 1.08 -- a nice improvement
 * both cards on the same 40-Mhz 386 with 8Mbytes RAM
 *
 * 	don't forget to include Casa Biegl's libgrx.a when compiling
*/
#include <stdio.h>

#include "e:/djgpp/contrib/libgrx/include/grx.h"
	/* change this path to wherever Casa Biegl's grx.h is */

#define screen_region_left_x 0
#define screen_region_bottom_y 0

double square (double num);
int pixel_x_distance (int pixel_x); 
int pixel_y_distance (int pixel_y);
double matching_x (int pixel_x, int square_left_x, int square_side_length);
double matching_y (int pixel_y, int square_bottom_y, int square_side_length);
int single_row_loop (int row_y, int column_x, int sq_left_x, int sq_bottom_y, int sq_side_length);
int choose_pen_color (int pix_x, int pix_y, int sq_left_x, int sq_bottom_y, int sq_side_length);
void region_loop (int row_y, int sq_left_x, int sq_bottom_y, int sq_side_length);
void circle_squared (int sq_left_x, int sq_bottom_y, int sq_side_length);
int max_x, max_y, x1, y1, zoom;

void main()
{
  printf("\n\n\nEnter the x and y coordinates and the zoom factor > "); 
  scanf("%d %d %d",&x1,&y1,&zoom);
  GrSetMode (GR_default_graphics); 
/*  GrSetMode (GR_width_height_graphics,640,480); */
  max_x=GrMaxX();
  max_y=GrMaxY();
  GrClearScreen(0);
  circle_squared (x1,y1,zoom); 
/* at 640 x 480 with 256 colors -> awesome!  circle_squared (-5,-5,250); */
/* at 1024 x 768 with 16 colors -> circle_squared (80,65,355); or 85 99 1200 look interesting */
  getchar();getchar(); 
/* extra getchar collects the enter key hit after scanf 
 * Note: once you hit enter the second time the graphics disapears
 * as the video mode is set to a text mode
*/
  GrSetMode (GR_default_text); 
/*  GrSetMode (GR_width_height_text,80,25); */
}

 double square (double num)
{
 double answer;
 answer = num*num;
 return answer;
}

 int pixel_x_distance (int pixel_x) 
{
 int answer;
 answer = pixel_x - screen_region_left_x;
 return answer;
}

 int pixel_y_distance (int pixel_y)
{
 int answer;
 answer = pixel_y - screen_region_bottom_y;
 return answer;
}

 double matching_x (int pixel_x, int square_left_x, int square_side_length)
{
 double answer, pixel_x_d;
 pixel_x_d=pixel_x_distance(pixel_x);
 answer = square_left_x + (square_side_length * (pixel_x_d / max_x));
 return answer; 
}

 double matching_y (int pixel_y, int square_bottom_y, int square_side_length)
{
 double answer, pixel_y_d;
 pixel_y_d=pixel_y_distance(pixel_y);
 answer = square_bottom_y + (square_side_length * (pixel_y_d / max_y));
 return answer;
}

 int single_row_loop (int row_y, int column_x, int sq_left_x, int sq_bottom_y, int sq_side_length)
{
 int pen_color;
pen_color=choose_pen_color (column_x,row_y,sq_left_x,sq_bottom_y,sq_side_length);
  if (column_x != max_x) 
{
GrPlot (column_x,row_y,pen_color);
single_row_loop (row_y,(1+ column_x),sq_left_x,sq_bottom_y,sq_side_length);
}
else return 0;
}

 int choose_pen_color (int pix_x, int pix_y, int sq_left_x, int sq_bottom_y, int sq_side_length)
{
 long answer, match_x, match_y;
 match_x=square(matching_x(pix_x,sq_left_x,sq_side_length));
 match_y=square(matching_y(pix_y,sq_bottom_y,sq_side_length));
 answer = (match_x + match_y) % 256;
 return answer; 
}

 void region_loop (int row_y, int sq_left_x, int sq_bottom_y, int sq_side_length)
{
  if (row_y >= max_y) 
	;
 else {
    single_row_loop (row_y, screen_region_left_x, sq_left_x, sq_bottom_y, sq_side_length);
    region_loop ((1+row_y), sq_left_x, sq_bottom_y, sq_side_length);
   }
}

 void circle_squared (int sq_left_x, int sq_bottom_y, int sq_side_length)
{
  region_loop (screen_region_bottom_y, sq_left_x, sq_bottom_y, sq_side_length);
}