Moving frame data, simple solution?

Newbie & Debugging Questions
#1

Hello folks!

I’ve been building a very basic program on my free time, just for fun, it basically draws random numbers in a line, then jumps to the next row when the line finishes. However, when reaching the bottom right part of the frame it continues down out of view. What i want it to do is move everything, numbers and background graphics upwards one line, then draw a new black square at the bottom row to draw the new numbers on. I looked around a bit in the Java API docs after a method that could do this for me and i found a method in the Graphics class called copyArea. This method moves everything but i can’t make it display the graphics properly, im unsure of what i am doing wrong. Could you guys help?

EDIT: I managed to fix it, im unsure how though XD

Here is the source


import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import javax.swing.JFrame;
import javax.swing.JPanel;
import java.util.*;

public class MainEngine extends JPanel implements Runnable{
	
	Random rand = new Random();
	
	int letterPosX, letterPosY;
	int number;
	boolean redraw = false;
	boolean running = true;
	boolean drawLetters = true;
	
	Graphics2D g2d;
	BufferedImage backbuffer;
	JPanel p1 = new JPanel();
	JFrame f = new JFrame();
	Thread CalcLoop;
	
	public static void main(String[] args){
		MainEngine me = new MainEngine();
		me.initCalculate();
	}
	
	public void initCalculate(){
		CalcLoop = new Thread(this);
		CalcLoop.start();	
	}
	
	@Override
	public void run() {

		initgfx();
		
		while(running == true){
			try{
				updateGraphics();
				repaint();
				Thread.sleep(1);
			}catch(InterruptedException e){}
		}
	}
	
	public void update(Graphics g){
		System.out.println("updating");
		paint(g);
	}
	
	

	
	public void initgfx(){
		backbuffer = new BufferedImage(800, 600, BufferedImage.TYPE_INT_RGB);
		g2d = backbuffer.createGraphics();
		f.setSize(800, 600);
		f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		f.getContentPane().add(this);
		f.setVisible(true);
		g2d.setColor(Color.BLACK);
		g2d.fillRect(0, 0, 800, 600);
	}
	
	public void updateGraphics(){
		
		if(drawLetters == true){
			g2d.setColor(Color.WHITE);
			number = rand.nextInt(10);
			g2d.drawString("" + number, letterPosX, letterPosY);
			letterPosX += 7;
		}
		if(letterPosX >= 790){
			letterPosX = 0;
			letterPosY += 11;
			
		}
		
		if(letterPosY >= 600){
			g2d.copyArea(0, 0, 800, 600, 0, -11);
			g2d.setColor(Color.BLACK);
			g2d.drawRect(0, 0, 800, 600);
			redraw = true;
			g2d.setColor(Color.WHITE);
			letterPosY = 589;
		}
		
		if(redraw != false){
			g2d.setColor(Color.BLACK);
			g2d.drawRect(0, 0, 800, 600);
			//running = false;
		}
	}
	
	public void updateLastPos(){

	}
	
	public void paint(Graphics g){
		g.drawImage(backbuffer, 0, 0, null);
	}
	
}
#2

I ran this on my computer and when the lines scrolled up, they overlapped the ones above them. After further investigation, I realized it was because the last line is still there after copying all the ones above. The fix is that you should replace line 87 on this code with:


g2d.fillRect(0,letterPosY-10,800,11);

And there is now no need for lines 93 to 97 since I don’t see the point of drawing a black rectangle around the whole thing.

Also, did you know you can just use boolean variables by themselves in any statement or loop that requires a boolean.
For example, you can:


//change
while(running == true) {

//to
while(running) {

//and
if(redraw != false) {

//is the same thing as
if(redraw == true) {

//which can be changed to
if(redraw) {
#3

I removed the black rectangle, it was just a failed attempt by me to get rid of the overlapping :stuck_out_tongue:

I just realized why it overlapped, just while posting this and looking through those exact lines you mentioned. I actually wanted to fill a rect, but somehow mistook that for drawrect, which explains why it was still overlapping even after i thought i filled a rect over the entire thing.

Thanks for the help ra4king :slight_smile:

Also, i’ll try to remember the boolean checks you presented since they seem easier to read and use :slight_smile:

#4

Glad to help :slight_smile: