Question

Using OpenGL develop a C code that a) draws a point that moves clockwise slowly along a circle with a center at (0,0). You may want to draw a circle first, and a point that moves on the circle with a different color. b) draws a 2D star inside the circle.

Answer 1

PROGRAM:

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(); 
}

//========================================================================

(B)

#include <GL/glut.h>

#include <GL/gl.h>
#include <GL/freeglut.h>

void init (void)
{
    glClearColor(0.0,0.0,0.0,00);
    glMatrixMode(GL_PROJECTION);
    gluOrtho2D(0.0,200.0,0.0,200.0);

}
void LineSegment(void)
{
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(1.0,1.0,1.0);
    glBegin(GL_LINE_LOOP);
    glVertex2i(20,120);
    glVertex2i(180,120);
    glVertex2i(45,20);
    glVertex2i(100,190);
    glVertex2i(155,20);
    glEnd();
    glFlush();
}
int main(int argc,char** argv)
{
    glutInit(&argc,argv);
    glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
    glutInitWindowPosition(50,100);
    glutCreateWindow("STAR");
    init();
    glutDisplayFunc(LineSegment);
    glutMainLoop();
    return 0;
}

//=======================================================================