Newbie Question: How to do circles with C

[Johanson]

I need help making a circle using only ASCII characters in a bidimensional array.
Thanks in advance

[Salem]

What sort of help?
- defining a 2D array?
- printing it
- putting some symbol at specific positions in the grid
- the function for the perimeter of a circle?

[Johanson]

I have everything working except the function for the perimeter of the circle.

[Salem]

x = r * cos( theta );
y = r * sin( theta );

[Johanson]

oooooooooooXXXXXX
ooooooooooXooooooX
oooooooooXooooooooX
oooooooooXooooooooX
oooooooooXooooooooX
oooooooooXooooooooX
oooooooooXooooooooX
oooooooooXooooooooX
ooooooooooXooooooX
oooooooooooXXXXXX

I used those and I got this. It is a circle but some time ago I saw an other way to get a better circle(don't remember where). Is there any algorithm to make a better circle?
Thanks for the help anyway

[Salem]

Post your code, that seems rather too octagonal.

Use [code][/code] tags when posting code (and your fixed-width output).

[Johanson]

void TestCircle(DRAWING draw,int a,int b,int r) /* DRAWING is a type of bidemensional arrays of the type char */
{ int x,y;
  double theta=0;
  
  for(;theta!=360.0 ;theta+=1)
  {
    x = a + r * cos( theta );
    y = b + r * sin( theta );
    des[x][y]='X';
  }
}

[cboard_member]

Just some cleanups

void TestCircle(DRAWING draw,int a,int b,int r) /* DRAWING is a type of bidemensional arrays of the type char */
{ 
  int x,y;  /* put nothing on the same line as a brace */
  double theta=0;
  
  for(;theta!=360.0 ;theta++)  /* ++ is the same as += 1 */
  {
    x = a + r * cos( theta );
    y = b + r * sin( theta );
    des[x][y]='X';
  }
}

I was bored. Again.
EDIT: And you have a space button for a reason. Jeeeeeesus.

[OnionKnight]

The problem is probably that you are outputting the circle on a console screen where the height of a character is about double the length of the width so you need to change that 2:1 ratio to 1:1 to get a circle instead of an oval.

[Salem]

> for(;theta!=360.0 ;theta+=1)
Additionally, the math trigonometry functions take radians, not degrees.
There are 2PI radians in a full circle, which means you go round about 60 times more than necessary.

[jafet]

@ahluka:
using operator++() on double theta is not really a good idea.

You might want to do (theta < 2*PI; theta += 0.1) to get some accuracy.

Console screen text is typically 8x4 pixels per character. One quick fix would be to create des[][] with half the width, then double it later. This wold however create a possibly-annoying "twin character syndrome".

[VirtualAce]

#define PI 3.14159
#define DEGTORAD(x) ( (x) * (PI) / (180.0) )

[joed]

Just for fun, here's an easy way to draw circles, adapted from "8088 Macro Assembler Programming" by Dan Rollins. Could be shortened/optimized a bit:

void circle(int x, int y, int r)
{
	int target = 0;
	int a = r;
	int b = 0;
	int dec, count;
	
	while(a > b) {
		b = (r * r - a * a);
		count = 0;
		dec = 1;
		while(b >= 0) {
			b -= dec;
			dec += 2;
			count++;
		}
		b = count;
		SWAP(target, b);
		while(b < target) {
			plot(x + a, y + b);
			plot(x - a, y + b);
			plot(x - a, y - b);
			plot(x + a, y - b);
			plot(x + b, y + a);
			plot(x - b, y + a);
			plot(x - b, y - a);
			plot(x + b, y - a);
			b++;
		}
		a--;
	}
}

[Johanson]

Just for fun, here's an easy way to draw circles, adapted from "8088 Macro Assembler Programming" by Dan Rollins. Could be shortened/optimized a bit:

void circle(int x, int y, int r)
{
	int target = 0;
	int a = r;
	int b = 0;
	int dec, count;
	
	while(a > b) {
		b = (r * r - a * a);
		count = 0;
		dec = 1;
		while(b >= 0) {
			b -= dec;
			dec += 2;
			count++;
		}
		b = count;
		SWAP(target, b);
		while(b < target) {
			plot(x + a, y + b);
			plot(x - a, y + b);
			plot(x - a, y - b);
			plot(x + a, y - b);
			plot(x + b, y + a);
			plot(x - b, y + a);
			plot(x - b, y - a);
			plot(x + b, y - a);
			b++;
		}
		a--;
	}
}

Thans a lot. This is exactly what I wanted

Edit:

The only problem is that when the radius=2, it won't work correctly. It shows this:

ooXoo
ooooo
XoooX
ooooo
ooXoo

[dwks]

http://www.brackeen.com/home/vga/shapes.html#shapes10.0