We Keep Coding

PaintComponent disrupting grid drawing

I'm new to Java as well as user interfaces, and I have a problem with Java Graphics. What I'm trying to achieve is drawing a grid on a JPanel, and then paint custom components into the grid.
Here is the class I want to draw the grid on (its base extends JPanel).
public class RectGridPanel extends GridPanel
{
List<Rectangle> rects;
public RectGridPanel(Simulator sim)
{
super(sim);
this.rects = new ArrayList<Rectangle>();
this.setLayout(new GridLayout(20,20));
for(int x = 1; x < 801; x += 40)
{
for(int y = 2; y < 801; y += 40)
{
Cell newCell = new RectCell(x, y, sim);
this.add(newCell);
}
}
}
#Override
public void paintComponent(Graphics g)
{
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setPaint(Color.BLACK);
for(int x = 1; x < 801; x += 40)
{
for(int y = 2; y < 801; y += 40)
{
Rectangle rect = new Rectangle(x, y, 40, 40);
g2.draw(rect);
rects.add(rect);
}
}
}
}
Here are the cells I want to draw inside the grid:
public class RectCell extends Cell
{
Rectangle shape;
public RectCell(int x, int y, Simulator sim)
{
super(x, y, sim);
shape = new Rectangle(x, y, CELL_SIZE, CELL_SIZE);
}
#Override
public void paintComponent(Graphics g)
{
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setPaint(Color.BLACK);
g2.fill(shape);
}
}
So the grid on its own draws out fine, but as soon as I try to create cells inside it it gets disrupted like that:

public class RectCell extends Cell
{
Rectangle shape;
public RectCell(int x, int y, Simulator sim)
{
super(x, y, sim);
shape = new Rectangle(x, y, CELL_SIZE, CELL_SIZE);
}
#Override
public void paintComponent(Graphics g)
{
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setPaint(Color.BLACK);
g2.fill(shape);
}
}
The Graphics object that is passed to this paintComponent() function defines the screen space where the current RectCell can draw. The coordinate sysetem is relative to the upper left corner of the RectCell, so drawing the background should always start at x = 0 and y = 0 or some other meaningful value. The coordinates here are not relative to the parent component as you seem to assume.
Better yet, set the background color and let Swing take care of painting it rather than painting a rectangle yourself.

It is not clear what you try to achive.
What is the reason for RectCell? Why not paint the shapes direct in the RectGridPanel?
The nested loop in the paintComponent it not a good idea. Be aware that the paintComponent is called very often and every time you in crease the rects list with new objects. The former painted rectangles get lost (qraphicaly) and new rectangles with the same parameters are blowing the list.

Restricting the drawing area on a JPanel and saving graphics states

The purpose of the black JPanel is drawing.
How can I restrict the drawing to the radius of the circle formed by the lines?
Is there a way to save the graphics object state so that more drawing can be added to it as well as adding an undo function?
public void paintComponent(Graphics g)
{
super.paintComponent(g);
sectors = 12;
Graphics2D g2d = (Graphics2D) g;
g2d.setColor(Color.RED);
sector = new Line2D.Double(getWidth()/2, 0, getWidth()/2, getHeight());
//g2d.setClip(new Ellipse2D.Double(getWidth()/2,getHeight()/2, radius, radius));
//draws the sectors on the screen
for(int i=0; i<sectors; i++)
{
g2d.draw(sector);
g2d.rotate(Math.toRadians(30),getWidth()/2,getHeight()/2);
}
//draws the doily
if(dragging)
{
for(int i=0; i<sectors; i++)
{
g2d.fillOval((int) draw.getX(), (int) draw.getY(),20, 20);
g2d.rotate(Math.toRadians(30), getWidth()/2, getHeight()/2);
}
//saves the current drawing in a stack
graphics.push(g2d);
}
}

For your first question,
You would need to read up on Java's Custom Painting http://docs.oracle.com/javase/tutorial/uiswing/painting/
Not to discourage you but this is a tricky process,
To answer your question there is a similar post here
Java Change shape of JPanel

How can I paint a custom circular JComponent without an "invisible box" around it?

I'm writing a JApplet that displays a diagram with numbers in circles and lines connecting the circles. I've created a class that extends JComponent to act as the circles. I overrode the paintComponent() method to draw a circle with the numbers inside, and I placed these circles on my applet, on which I drew the lines in the paint() method.
However, if the lines hit the circle at an angle, they cut out early, before the circle, at the square that outlines the entire JComponent, even though the background should be transparent. this forms an "invisible box" around the circle.
I've prepared a smaller program to demonstrate the issue:
And here is the code for that example:
import java.awt.*;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Line2D;
import javax.swing.*;
public class Circle extends JApplet {
private static final long serialVersionUID = 1L;
myCircle myC = new myCircle(10, 215, 215); // custom circle
Container c;
public void init() {
setSize(500, 500);
c = getContentPane();
c.setLayout(null);
c.setBackground(Color.lightGray);
c.add(myC);
}
public void paint(Graphics g) {
super.paint(g);
Graphics2D g2d = (Graphics2D)g;
g2d.setRenderingHint(
RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2d.setColor(Color.black);
g2d.setStroke(new BasicStroke(2f, BasicStroke.CAP_BUTT, BasicStroke.JOIN_MITER));
//draw lines
g2d.draw(new Line2D.Double(0f, 0f, 500f, 500f));
g2d.draw(new Line2D.Double(0f, 500f, 500f, 0f));
g2d.draw(new Line2D.Double(0f, 250f, 500f, 250f));
g2d.draw(new Line2D.Double(250f, 0f, 250f, 500f));
g2d.draw(new Line2D.Double(150f, 0f, 350f, 500f));
myC.repaint(); // put the circle on top
}
public class myCircle extends JComponent {
private static final long serialVersionUID = 1L;
int number; // number to display
public myCircle(int num, int x, int y) {
this.number = num;
this.setLocation(x, y);
this.setSize(75, 75);
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D)g;
g2d.setRenderingHint(
RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2d.setRenderingHint(
RenderingHints.KEY_TEXT_ANTIALIASING,
RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
g2d.setStroke(new BasicStroke(2f, BasicStroke.CAP_BUTT, BasicStroke.JOIN_MITER));
g2d.setColor(Color.white);
g2d.fill(new Ellipse2D.Float(1f, 1f, 70f, 70f));
g2d.setColor(Color.black);
g2d.draw(new Ellipse2D.Float(1f, 1f, 70f, 70f));
g2d.drawString(Integer.toString(number), 15f, 20f);
}
}
}

I wouldn't use a component to represent the circle shape alone. Instead, just paint it all on one JPanel (I'm using a JFrame instead of an applet):
public class Circle extends JPanel {
int number = 10;
float size = 500f;
float rad = 70f;
float stringLocX = 15f, stringLocy = 20f;
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
g2d.setColor(Color.LIGHT_GRAY);
g2d.fillRect(0, 0, getWidth(), getHeight());
g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
g2d.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING, RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
g2d.setStroke(new BasicStroke(2f, BasicStroke.CAP_BUTT, BasicStroke.JOIN_MITER));
g2d.setColor(Color.BLACK);
g2d.draw(new Line2D.Double(0f, 0f, size, size));
g2d.draw(new Line2D.Double(0f, size, size, 0f));
g2d.draw(new Line2D.Double(0f, size / 2, size, size / 2));
g2d.draw(new Line2D.Double(size / 2, 0f, size / 2, size));
g2d.draw(new Line2D.Double(150f, 0f, 350f, 500f));
Ellipse2D.Float circle = new Ellipse2D.Float((size - rad) / 2, (size - rad) / 2, rad, rad);
g2d.setColor(Color.WHITE);
g2d.fill(circle);
g2d.setColor(Color.BLACK);
g2d.draw(circle);
g2d.drawString(Integer.toString(number), (size - rad) / 2 + stringLocX,
(size - rad) / 2 + stringLocy);
}
#Override
public Dimension getPreferredSize() {
return new Dimension((int) size, (int) size);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(() -> {
JFrame frame = new JFrame();
frame.add(new Circle());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setVisible(true);
});
}
}
Depending on how many circles you have and what data they must contain, you can just keep a list of those numbers, then iterate over the list in painComponent and draw them.
Notes:
Don't use null layout.
Better to keep the hard coded numbers as fields so you can change them more easily, possibly make them final.

You need to look at the length of the line being drawn. From the edge of your figure to the circle is longer at an angle than at the sides. Recall for a triangle with 45 degrees, 45 degree, and 90 degree angles the ratio of the length of the sides is 1:1:sqrt(2)

Creating images with a java

Hello) Help solve the problem:
We need to create a green square image and display it.
I could draw a square, but I need to create it using java.
Please help me to do this)
That's what I tried to do:
import java.awt.Canvas;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import javax.swing.JFrame;
public class Game extends Canvas {
private static final long serialVersionUID = 1L;
private static final int WIDTH = 400;
private static final int HEIGHT = 400;
#Override
public void paint(Graphics g) {
super.paint(g);
int w = 10;
int h = 10;
int type = BufferedImage.TYPE_INT_ARGB;
BufferedImage image = new BufferedImage(w, h, type);
int color = 257; // RGBA value, each component in a byte
for (int x = 1; x < w; x++) {
for (int y = 1; y < h; y++) {
image.setRGB(x, y, color);
g.drawImage(image, 0, 0, getWidth(), getHeight(), null);
}
}
}
public static void main(String[] args) {
JFrame frame = new JFrame();
frame.setSize(WIDTH, HEIGHT);
frame.add(new Game());
frame.setVisible(true);
}
}
But nothing is displayed (
Let me remind the goal - to create a picture in the form of green squares, help to make it)

The simplest approach would be to simply use the graphics API...
#Override
public void paint(Graphics g) {
super.paint(g);
int w = 10;
int h = 10;
g.setColor(Color.GREEN);
g.fillRect(0, 0, width, height);
}
But something tells me this isn't what you want, but it does form the basics for what you need to achieve your result.
Start by making image a instance field...
private BufferedImage image;
Then you need to create the image...
int type = BufferedImage.TYPE_INT_ARGB;
image = new BufferedImage(w, h, type);
Graphics2D g2d = image.createGraphics();
g2d.setColor(Color.GREEN);
g2d.fillRect(0, 0, w, h);
g2d.dispoe();
Then in you paint method, you need to draw the image...
g.drawImage(image, x, y, this);
Take a look at the 2D Graphics trail for mor details

You must use Graphics.drawRect() and Graphics.fillRect():
http://docs.oracle.com/javase/7/docs/api/java/awt/Graphics.html#drawRect%28int,%20int,%20int,%20int%29
http://docs.oracle.com/javase/7/docs/api/java/awt/Graphics.html#fillRect%28int,%20int,%20int,%20int%29

if you want to create an Image with rectangle containing it, first create the image, draw on it using it's graphics. I am writing code snippets for you:
BufferedImage image = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
Graphics g = image.getGraphics();
g.setColor(Color.blue);
g.fillRect(0, 0, image.getWidth(), image.getHeight());
This will produce an image with Blue rectangle.

Drawing a shape but keeping the most previous shape on screen in java

I've created a function to where I can click somewhere in a Jpanel and it draws a shape at the position where the mouse clicked. The problem I am having is when I click in a new position, it moves the shape and redraws it. I would like the previous shape to "Burn" into the screen and stay there. It doesn't have to have any data tied to it, I just want the image of the shape to show where it used to be each time. I have tried many different things, but no success. here is what I mean:
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setColor(Color.BLUE);
g2.fillRect(n, m, 32, 32); //I want each one of these shapes to be new, not
//moving, but redrawn
////////////////////////////////////////////////
//This is just drawing a grid and doing other things(irrelevant)
g2.fill(new Ellipse2D.Double(x, y, 32, 32));
for (int i = 0; i < 500; i += 32) {
g2.drawRect(i, j, 32, 32);
for (int j = 0; j < 500; j += 32) {
g2.drawRect(i, j, 32, 32);
}
}
if (paintColBlock){
System.out.println("Drawing Block at " + n +"," + m);
paintColBlock = false;
}
/////////////////////////////////////////////////////////////////////
}

Keep an ArrayList of Points like this:
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setColor(Color.BLUE);
for(Point p : points)
g2.fillRect(p.x, p.y, 32, 32);
Adding a new Point to the array at each mouse click, and call repaint():
public void mousePressed(MouseEvent evt){
points.add(new Point(evt.getX(),evt.getY());
repaint();
}