How to detect and change shape in Java OpenGL

Question

I drew some shapes using OpenGL, here is the code:

The drawing methods:

private void drawRectangle(GL2 gl, double x1, double y1, double x2, double y2, double x3, double y3, double x4, double y4) {
        gl.glBegin(GL2.GL_LINE_LOOP);
        gl.glVertex2d(x1, y1);
        gl.glVertex2d(x2, y2);
        gl.glVertex2d(x3, y3);
        gl.glVertex2d(x4, y4);
        gl.glEnd();
    }

private void drawCircle(GL2 gl, double centerX, double centerY, double radius) {
        gl.glBegin(GL2.GL_LINE_STRIP);
         for (double i = 0; i < 360; i++) {
             double radian = i * Math.PI / 180;
             double x = radius * Math.cos(radian) + centerX;
             double y = radius * Math.sin(radian) + centerY;

             gl.glVertex2d(x, y);
         }
         gl.glEnd();
    }

I drew some circles and rectangles, here is the display method:

public void display(GLAutoDrawable drawable) {
        final GL2 gl = drawable.getGL().getGL2();
        gl.glColor3f(1f, 1f, 1f);
        
        drawCircle(gl, 0.7, 0.2, 0.1);
        drawCircle(gl, 0.3, 0.1, 0.3);
        drawRectangle(gl, -0.5, -0.5, 0, -0.5, 0, 0, -0.5, 0);
    }

The displayed result:

I want to fill the shape with a color when I click on it. (static color for all clicks, red for example)

class Color {
    public double c1, c2, c3;

    public Color(double c1, double c2, double c3) {
        super();
        this.c1 = c1;
        this.c2 = c2;
        this.c3 = c3;
    }
}

So I want to know 2 things:
1- how can I fill the shape with a color?
2- how to fill the shape when I click on it?

I'm using javax.swing.JFrame to show the canvas, but there is no problem if there is a way using anything else such as JavaFX or AWT or something else.

---

The main method:

public static void main(String[] args) {
        final GLProfile profile = GLProfile.get(GLProfile.GL2);
        GLCapabilities capabilities = new GLCapabilities(profile);
        final GLCanvas glcanvas = new GLCanvas(capabilities);
        Driver driver = new Driver();
        glcanvas.addGLEventListener(driver);
        glcanvas.setSize(400, 400);

        final JFrame frame = new JFrame();
        frame.getContentPane().add(glcanvas);
        frame.setSize(frame.getContentPane().getPreferredSize());
        frame.setVisible(true);
    }

Answer 1

If you want to fill the shape with a color, you must use one of the Triangle primitives instead of GL2.GL_LINE_LOOP. e.g.: GL2.GL_TRIANGLE_FAN:

gl.glBegin(GL2.GL_TRIANGLE_FAN);
gl.glVertex2d(x1, y1);
gl.glVertex2d(x2, y2);
gl.glVertex2d(x3, y3);
gl.glVertex2d(x4, y4);
gl.glEnd();

gl.glBegin(GL2.GL_TRIANGLE_FAN);
for (double i = 0; i < 360; i++) {
    double radian = i * Math.PI / 180;
    double x = radius * Math.cos(radian) + centerX;
    double y = radius * Math.sin(radian) + centerY;
    gl.glVertex2d(x, y);
}
gl.glEnd();