how to draw the 6 petals of a flower?

[ronald deux]

import java.awt.Graphics2D;

import javax.swing.JFrame;

public class RoseCurve {
	
	
	void drawRoseCurve(Graphics2D g2d, int k, double x, double y, double theta) {
		
		double r = Math.cos(k*theta);
		
		x = r*(Math.sin(theta));
		y = r*(Math.cos(theta));
		
	}
	
	public static void main(String[] args) {
		
		JFrame frame = new JFrame();
		
		frame.setSize(900,600);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setLocationRelativeTo(null);
		frame.setVisible(true);
	}

}

here is a piece of code, after I don't know how to do this project, I looked in the API, however I know that you need a g2d.draw or g.draw to draw

[Piet Souris]

A couple of months ago I drew many colored petals of a flower> golden daisies

[ronald deux]

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.RenderingHints;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class RoseCurve extends JPanel {
	

	public void drawRoseCurve(Graphics2D g2d) {
		
		g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
	    //g2d.setColor(Color.white);
	    //g2d.fillRect(0, 0, WIDTH, HEIGHT);
		
		double x = 0;
		double y = 0;
		
		g2d.setColor(Color.blue);
        g2d.setStroke(new BasicStroke(4));
        
		for (int theta = 0; theta <= 360; theta++) {
		double k = theta * Math.PI / 180;
		double r = Math.cos(k*theta);
		
		double newX = r*(Math.sin(k));
		double newY = r*(Math.cos(k));
		g2d.drawLine((int)x, (int)y, (int)newX, (int)newY);
        x = newX;
        y = newY;
		
	}
}

	public static void main(String[] args) {
		
		JFrame frame = new JFrame();
		frame.getContentPane().add(new RoseCurve());
		
		frame.setSize(900,600);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setLocationRelativeTo(null);
		frame.setVisible(true);
	}
}

what do you think of this code?
a little help would be welcome, what should be changed or what should be put as a method or other, I do not want any code otherwise I will not move forward

[Norm Radder]

Also posted here: https://www.dreamincode.net/forums/topic/419770-how-to-draw-the-6-petals-of-a-flower/

[Campbell Ritchie]

Moved to our GUIs forum.

Have you looked through the methods of Graphics, and the different classes in the java.awt.geom package? You may find something for drawing such curves without having to mess about with loops.
Don't divide by π; use the methods of the Math class for converting degrees and radians.
The fact that you have to convert ints to doubles and vice versa is a problem with Swing® which you mightn't suffer with FX.

[Piet Souris]

Some remarks:

Math.cos (and sin and tan) works with radians. So, line 25 and 26 might not do what you expect it to do.

Line 26 limits the values of r to the interval [-1, 1], and so, newX and newY are also limited to that interval. That mens that your drawings appear in the upper left corner of your panel, hardly to see.

In the code I pointed to yesterday, I did two things to get the effect: first, I set the origin of the panel to the midpoint of it, and second I draw the same ellips over and over, but between two ellipses I rotate a little.

If I do that here, and use ellipses for simplicity, then this is what I got:

public void drawRoseCurve(Graphics2D g2d) {
    g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    g2d.setStroke(new BasicStroke(2));
    g2d.translate(this.getWidth() / 2, this.getHeight() / 2);
    for (int i = 0; i < leaves; i++) {
        g2d.rotate(Math.PI * 2 / leaves);
        drawLeave(g2d, Color.RED, Color.BLACK);
    }
    g2d.setColor(Color.red.darker());
    g2d.fillOval(-30, -30, 60, 60);
    g2d.setColor(Color.BLACK);
    g2d.drawOval(-30, -30, 60, 60);
}

and

private void drawLeave(Graphics2D g2d, Color fill, Color rim) {
    g2d.setColor(fill);
    g2d.fillOval(0, -ellipsHeight / 2, ellipsWidth, ellipsHeight);
    g2d.setColor(rim);
    g2d.drawOval(0, -ellipsHeight / 2, ellipsWidth, ellipsHeight);
}

Admitted, it looks not like a rose, but it is a start.

Your idea is certainly interesting. Letting the angle go from 0 to PI, and setting r to say 200 * Math.sin(angle), and  calculating x and y as if r and angle were polar coordinates. Such techniques give a lot of modelling possibilities. Another idea is to work with Path2D. Using Bezier curves might give nice leaves too. But to get something that looks like a rose, hmmm. Maybe the guys at DreamInCode have some ideas.

[ronald deux]

import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JFrame;

public class Test extends JFrame {
	
	static double n = 6;
	
	public Test() {
	
		super("Test");
        setBounds(100, 100, 800, 600);
        setResizable(false);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
	}
	
    private void drawTest(Graphics g, int x1, int y1) {
    	
    	g.translate(this.getWidth() / 2, this.getHeight() / 2);
    	
		for (int theta = 0; theta <= 360; theta++) {
			double k = theta * Math.PI / 180;
			double r = 300*(Math.sin(k*n));
		
			double x2 = r*(Math.cos(k));
			double y2 = r*(Math.sin(k));
		
			g.drawLine((int)x1,(int)y1,(int)x2,(int)y2);
		
			x1 = (int) x2;
			y1 = (int) y2;
		}
	}
	
	public void paint(Graphics g) {
		g.setColor(Color.BLUE);
		drawTest(g, 400, 500);
    }
 
	public static void main(String[] args) {
        new Test().setVisible(true);
    }
}

I almost succeeded, on the other hand a straight line which goes down diagonally,

[Piet Souris]

Very nice indeed!

To get rid of that line, just issue

drawTest(g, 0, 0);

[ronald deux]

I found
thank you

[Norm Radder]

Another idea for the project - using a timer call drawline every x milliseconds to draw the next segment of the drawing so that you can see the pedals being drawn as it happens instead of drawing the lines all at once.

[Piet Souris]

just put:

try {
    Thread.sleep(30);  
}
catch (Exception e) {}

right before the g.drawLine

[Campbell Ritchie]

Would you want to sleep that Thread, Piet?

[Piet Souris]

Never do: Thread.sleep on the EDT. This case is the exception that confirms the rule.

Norm wanted to see the drawing happening, and this is a very easy way to get that done. The drawing is just a one-off thing (the frame is not resizable), and so it is justified. Well, my opinion, that is.

But I guess the whole thing still is mysterious, even if you see it happening right before your eyes. Then use a spreadsheet, use many values for the angle from 0 to 2*PI, set a column of corresponding r-values, and make a graph of the angles with the r's. Another idea is: find your Spirograph box, and see if you can reproduce a similar figure.

[ronald deux]

I will try, I know the spirograph
I just tried your code
it works

[Piet Souris]

My code to slow down the drawing worked, becauce that code was not running on the EDT, Well, never mind.

Have you found out about getting 6 petals, as your qriginal question was? In your working code, you have that

r = 300 * Math.cos(6 * angle);

So, when angle = 0, r = 300, and when angle = 15 degrees, r = 0, since cos(6 * 15 degrees) = 0;

Tha means that in steps of 15 degrees, we get half a petal, and therefore in steps of 30 degrees we get a full petal. There are 12 steps of 30 degrees in 360 degrees, and that is why you see 12 petals. Can you find out how to get 6 petals?

This method (r = 300 * cos(factor * angle) works nicely, as long as factor is a divisor of 90. It is not easy to get this method to deliver a random number of petals.

I mentioned the possible use of a Path2D object, that represents a leave. You can have without effort any number of petals and it is quite fast. I made a demo. The leave here is a Path2D that is made of two slightly different quadratic Bezier curves. Well, enjoy.

public class RonaldDeux {
    
    public static void main(String... args) {
        SwingUtilities.invokeLater(RonldDeux::new);
    }
    
    JPanel panel;
    int panelWidth = 500;
    int panelHeight = 500;
    int petals = new Random().nextInt(50) + 3;
    JTextField textField = new JTextField(" " + petals + " ");
    Path2D leave;
    Font font = new Font("Helvetica", Font.BOLD, 16);
    
    RonaldDeux() {
        leave = createLeave(petals);

        panel = new JPanel() {
            @Override
            protected void paintComponent(Graphics g) {
                super.paintComponent(g);
                var g2d = (Graphics2D) g.create();
                g2d.translate(this.getWidth() / 2, this.getHeight() / 2);
                g2d.setColor(Color.pink);
                double deltaAngle = 2 * PI / petals;
                for (int i = 1; i <= petals; i++) {
                    g2d.rotate(deltaAngle);
                    g2d.fill(leave);
                }
                g2d.dispose();
            };
            
            @Override
            public Dimension getPreferredSize() {
                return new Dimension(panelWidth, panelHeight);
            }
        };
        
        var buttonPanel = new JPanel();
        var label = new JLabel("nr of petals: ");
        label.setFont(font);
        var minusButton = createButton(" - ", a -> a - 1);
        var plusButton = createButton(" + ", a -> a + 1);
        textField.addActionListener(ae -> processNumber(a -> a, false));
        textField.setFont(font);
        buttonPanel.add(label);
        buttonPanel.add(minusButton);
        buttonPanel.add(textField);
        buttonPanel.add(plusButton);
        buttonPanel.setBackground(Color.green);
        
        var f = new JFrame();
        var c = f.getContentPane();
        c.add(buttonPanel, PAGE_START);
        c.add(panel, CENTER);
        
        f.pack();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }
    
    private Path2D createLeave(int nrOfPetals) {
        var leave = new Path2D.Double();
        double radius = Math.min(panelWidth / 3, panelHeight / 3);
        leave.moveTo(0, 0);
        leave.quadTo(radius *PI / nrOfPetals, radius * .9, 0, radius);
        leave.quadTo(-radius * .8 * PI / nrOfPetals, radius * .9, 0, 0);
        leave.closePath();
        return leave;
    }
    
    private JButton createButton(String text, IntUnaryOperator iuo) {
        var button = new JButton(text);
        button.setFont(font);
        button.addActionListener(ae -> processNumber(iuo, true));
        return button;
    }
    
    private void processNumber(IntUnaryOperator iuo, boolean fromButton) {
        petals = fromButton ? iuo.applyAsInt(petals) : 
                              Integer.parseInt(textField.getText().trim())
        ;
        petals = petals < 1 ? 1 : petals > 50 ? 50 : petals;
        textField.setText(String.format("%3d", petals));
        leave = createLeave(petals);
        panel.repaint();
    }
}

[ronald deux]

no, I must have asked the question too quickly,
I thought it would give a 6 petal rose
otherwise thank you for the code