How to draw arc in opengl using x, y position, radius, start angle and end angle.

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Draw an arc using x,y position, Radius, Start Angle and End Angle in OpenGL

x (center x position of the circle)
y (center y position of the circle)
r (Radius)
Start_Angle (The angle (referenced from the center of the circle) that defines the start
position of the arc.)
End_Angle (The angle (referenced from the center of the circle) that defines the end
position of the arc.)

What I have tried:

I have tried this...

C#

void DrawArc(float cx, float cy, float r, float start_angle, float arc_angle, int num_segments) 
{ 
   float theta = arc_angle / float(num_segments - 1);//theta is now calculated from the arc angle instead, the - 1 bit comes from the fact that the arc is open

   float tangetial_factor = tanf(theta);

   float radial_factor = cosf(theta);


   float x = r * cosf(start_angle);//we now start at the start angle
   float y = r * sinf(start_angle); 

   glBegin(GL_LINE_STRIP);//since the arc is not a closed curve, this is a strip now
   for(int ii = 0; ii < num_segments; ii++)
   { 
      glVertex2f(x + cx, y + cy);

      float tx = -y; 
      float ty = x; 

      x += tx * tangetial_factor; 
      y += ty * tangetial_factor; 

      x *= radial_factor; 
      y *= radial_factor; 
   } 
   glEnd(); 
}

but its not satisfying my requirement.

Posted 17-May-16 22:24pm

stenco99

Updated 20-May-16 6:57am

phil.o

v2

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Herman<T>.Instance 18-May-16 5:23am

but its not satisfying my requirement. ?????

phil.o 18-May-16 7:11am

Please describe in what the result you get is not satisfying.

Patrice T 18-May-16 20:19pm

define 'your requirement'

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Richard MacCutchan · Answer 1 · 2016-05-18T00:38:00

Solution 1

See Draw an arc opengl - Google Search[^].

Posted 18-May-16 0:38am

Richard MacCutchan

stenco99 · Answer 2 · 2016-05-18T22:29:00

GL.Begin(PrimitiveType.LineStrip);
double x = 2.047;
double y = 3.5;
double r = .5;
double start_angle = 1.5;
double end_angle = 3.2;
double max_angle = 2 * Math.PI;
double angle_increment = Math.PI / 1000;
for (double theta = start_angle; theta < end_angle; theta += angle_increment)
{

x = r * Math.Cos (theta);
y = r * Math.Sin (theta);
GL.Vertex2(x, y);
}
GL.End();

*******************************************************************************
Could draw the arc, but became oval in shape. please help to draw a proper arc.

Patrice T · Answer 3 · 2016-05-20T06:57:00

Your solution don't respect your requirements.

Quote:

x (center x position of the circle)
y (center y position of the circle)

You need to make changes like that:

C#

GL.Begin(PrimitiveType.LineStrip);
    double x = 2.047;
    double y = 3.5;
    double r = .5;
    double start_angle = 1.5;
    double end_angle = 3.2;
    double max_angle = 2 * Math.PI;
    double angle_increment = Math.PI / 1000;
    for (double theta = start_angle; theta < end_angle; theta += angle_increment)
    {

        //x = r * Math.Cos (theta);
        //y = r * Math.Sin (theta);
        GL.Vertex2(x+  r * Math.Cos (theta), y+ r * Math.Sin (theta));
    }
    GL.End();

How to draw arc in opengl using x, y position, radius, start angle and end angle.

3 solutions

Solution 1

Solution 2

Solution 3

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