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Program to Draw an Ellipse using Mid - Point Algorithm


#include <stdio.h>
#include <dos.h>
#include <graphics.h>
void ellipseMidpoint(float, float, float, float);
void drawEllipse(float, float, float, float);
void main()
{
float xc, yc, rx, ry;
int gd = DETECT, gm;
initgraph(&gd, &gm, "");
printf("\nEnter the center coordinates of ellipse: ");
scanf("%f %f", &xc, &yc);
printf("\nEnter x-radius coordinate: ");
scanf("%f", &rx);
printf("\nEnter y-radius coordiante: ");
scanf("%f", &ry);
ellipseMidpoint(xc, yc, rx, ry);
getch();
}
void ellipseMidpoint(float xc, float yc, float rx, float ry)
{
float rxSq = rx * rx;
float rySq = ry * ry;
float x = 0, y = ry, p;
float px = 0, py = 2 * rxSq * y;
drawEllipse(xc, yc, x, y);
//Region 1
p = rySq - (rxSq * ry) + (0.25 * rxSq);
while (px < py)
{
x++;
px = px + 2 * rySq;
if (p < 0)
p = p + rySq + px;
else
{
y--;
py = py - 2 * rxSq;
p = p + rySq + px - py;
}
drawEllipse(xc, yc, x, y);
delay(30);
}
//Region 2
p = rySq*(x+0.5)*(x+0.5) + rxSq*(y-1)*(y-1) - rxSq*rySq;
while (y > 0)
{
y--;
py = py - 2 * rxSq;
if (p > 0)
p = p + rxSq - py;
else
{
x++;
px = px + 2 * rySq;
p = p + rxSq - py + px;
}
drawEllipse(xc, yc, x, y);
delay(30);
}
}
void drawEllipse(float xc, float yc, float x, float y)
{
putpixel(xc+x, yc+y, RED);
putpixel(xc-x, yc+y, RED);
putpixel(xc+x, yc-y, RED);
putpixel(xc-x, yc-y, RED);
}

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