Write a routine to draw a circle ?

Kamal Verma

Hi guys,

What a routine to draw a circle (x ** 2 + y ** 2 = r ** 2) without making use of any floating point computations at all.

Thanks

2 Replies

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Vulpes15y ago
Oops, forgot to generate the points for negative values of y.

Here's the revised code - points generated in clockwise order:

using System;

struct Point
{
public int X, Y;

public Point(int x, int y)
{
X = x;
Y = y;
}

public override string ToString()
{
return String.Format("({0}, {1})", X, Y);
}
}

class Circle
{
static void Main()
{
Console.Write ("Enter radius : ");
int r;
int.TryParse(Console.ReadLine(), out r);
if (r <= 0)
{
Console.WriteLine("Radius must be > 0");
return;
}

/*
assuming center of circle is at origin (0,0)
generate points (x, y) to draw circle
*/

Point[] points = new Point[4 * r];
int y;

for(int x = - r; x <= 0; x++)
{
y = Sqrt(r * r - x * x);
points[x + r] = new Point(x, y);
}

// the y values will be symmetric for x == 1 to x == r
for(int x = 1; x <= r; x++)
{
y = points[r - x].Y;
points[x + r] = new Point(x, y);
}

// the points for negative values of y will be symmetric with those for postive values

for (int x = r - 1; x >= - r + 1; x--)
{
y = - points[r + x].Y;
points[3 * r - x] = new Point(x, y);
}

// print results
Console.Clear();
foreach(Point p in points) Console.WriteLine(p);
Console.ReadKey();
}

static int Sqrt(int ys)
{
int t2 = 0;
while (t2 * t2 < ys) t2++;
if (ys == t2 * t2) return t2;
int t1 = t2 - 1;
int d2 = t2 * t2 - ys;
int d1 = ys - t1 * t1;
if (d2 < d1) return t2;
return t1;
}
}
0
Vulpes15y ago
Here's a possible way to generate the points to draw a circle of a given radius, with center at the origin using only integer arithmetic. Of course, for a given x value, we can only express y to the nearer integer unless r^2 - x^2 is an exact square.

using System;

struct Point
{
public int X, Y;

public Point(int x, int y)
{
X = x;
Y = y;
}

public override string ToString()
{
return String.Format("({0},{1})", X, Y);
}
}

class Circle
{
static void Main()
{
Console.Write ("Enter radius : ");
int r;
int.TryParse(Console.ReadLine(), out r);
if (r <= 0)
{
Console.WriteLine("Radius must be > 0");
return;
}

/*
assuming center of circle is at origin (0,0)
generate points (x, y) to draw circle
*/

Point[] points = new Point[2 * r + 1];
int y;

for(int x = - r; x <= 0; x++)
{
y = Sqrt(r * r - x * x);
points[x + r] = new Point(x, y);
}

// the y values will be symmetric for x == 1 to x == r
for(int x = 1; x <= r; x++)
{
y = points[r - x].Y;
points[x + r] = new Point(x, y);
}

// print results
Console.Clear();
foreach(Point p in points) Console.WriteLine(p);
Console.ReadKey();
}

static int Sqrt(int ys)
{
int t2 = 0;
while (t2 * t2 < ys) t2++;
if (ys == t2 * t2) return t2;
int t1 = t2 - 1;
int d2 = t2 * t2 - ys;
int d1 = ys - t1 * t1;
if (d2 < d1) return t2;
return t1;
}
}
0