OpenGL doesn’t seem to have any functions for drawing an unfilled circle, so you can use this code instead. It uses lines, so you can adjust the line thickness with glLineWidth and anti-alias it with glEnable(GL_LINE_SMOOTH) if you want.
void drawCircle(GLfloat x, GLfloat y, GLfloat r) {
static const double inc = M_PI / 12;
static const double max = 2 * M_PI;
glBegin(GL_LINE_LOOP);
for(double d = 0; d < max; d += inc) {
glVertex2f(cos(d) * r + x, sin(d) * r + y);
}
glEnd();
}
static const double inc = M_PI / 12;
static const double max = 2 * M_PI;
glBegin(GL_LINE_LOOP);
for(double d = 0; d < max; d += inc) {
glVertex2f(cos(d) * r + x, sin(d) * r + y);
}
glEnd();
}
If you want a filled circle, I would suggest you just set glPointSize to whatever size you want, and then plot a single point with glBegin(GL_POINTS) where ever you want your circle. Otherwise, you can use the above code with GL_POLYGON if you want more control. If you want a smoother circle, decrease the size of “inc”.
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