Drawing a circle using glut...

This is a discussion on Drawing a circle using glut... within the C Programming forums, part of the General Programming Boards category; I can't seem to draw a circle using glut... anybody knows how to do it... thanx in advance. I think ...

  1. #1
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    Drawing a circle using glut...

    I can't seem to draw a circle using glut... anybody knows how to do it... thanx in advance. I think i know the logic and that is to split the circle into individual small lines and outputting them...

  2. #2
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    My original code is this
    PHP Code:
    void function(void){
        
    float calculate (float);

        
    float x,y;
        
    int i;
        
    glClearColor(1.00.01.00.0);    
        
    glClear(GL_COLOR_BUFFER_BIT);    
        
        
        
    /*Draw axes*/
        
    glColor3f(1.0,1.0,1.0);        //black color

        
    glLineWidth(5); //5 pixels

        /*Perform drawing of axes*/

        
    glBegin(GL_LINES);
        
    glVertex2f(0,1);
        
    glVertex2f(0,-1);

        
    glVertex2f(1,0);
        
    glVertex2f(-1,0);

        
    glEnd();
        
        
    /*Draw Circle*/
        
        
    glColor3f(0.0,0.0,1.0);
        
    glBegin(GL_LINES);
        
    glLineWidth(3);
        
        for(
    i=0;i<=500;i++) //no of short lines to be drawn
        
    {
            
    radius + (i-1)*0.002;
            
    ycalculate(x);
            
    /*scale*/
            
    x1;
            
    y-1;

            
    glVertex2f(x,y);

            
    radius i*0.002;
            
    ycalculate(x);
            
    x1;
            
    y-1;
            
    glVertex2f(x,y);
        }
        
    glEnd();
        
    glFlush();

    }

    float calculate(float x)
    {
        return 
    radius x//pow(x,2) + pow(y,2) = pow(r,2)
                            //y = r - x

    I feel the codes a little weird at the circle area. the axes are all right.
    Last edited by bennyho03; 10-17-2004 at 12:13 PM.

  3. #3
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    if you want to do it without floating point calculations look into Bressenhams Circle Drawing Algorithm

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    Code:
    	float x,y;
    	float radius = 0.5f;
    	glBegin(GL_LINES);
    		glColor3f(0.0f,0.0f,0.0f);
    		
    		x = (float)radius * cos(359 * PI/180.0f);
    		y = (float)radius * sin(359 * PI/180.0f);
    		for(int j = 0; j < 360; j++)
    		{
    			glVertex2f(x,y);
    			x = (float)radius * cos(j * PI/180.0f);
    			y = (float)radius * sin(j * PI/180.0f);
    			glVertex2f(x,y);
    		}
    	glEnd();

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    thanx for the help but there is a another question though. Why is there a 'f' at the end of
    float radius = 0.5f
    ? Thanx

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    That is because (at least what I have heard) otherwise the number would default to double and you would (possibly) get a warning. I am not sure though since I dont program in C, I am a C++ guy so I am not too familiar with C standard.

  7. #7
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    maybe your reasoning is right since double is long float. Thanx anyway

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