Java Graphics setColor does not work

Question

I am trying to implement a plot of a Julia Set using a Canvas inside a JFrame. For some reason it seems that setColor() does not work. Here's the responsible code:

@Override
public void paint(Graphics aGraphics) 
{
    // store on screen graphics
    Graphics cScreenGraphics = aGraphics;
    // render on background image
    aGraphics = m_cBackGroundImage.getGraphics();

    for(int i = 0; i < m_iWidth; i++) 
    {
        for(int j = 0; j < m_iHeight; j++) 
        {
            int r = m_iPixelRed[i][j];
            int g = m_iPixelGreen[i][j];
            int b = m_iPixelBlue[i][j];
            aGraphics.setColor(new Color(r, g, b));
            aGraphics.drawRect(i, j, 0, 0);
        }
    }
    // rendering is done, draw background image to on screen graphics
    cScreenGraphics.drawImage(m_cBackGroundImage, 1, 1, null);
}

At first I suspected that the values were not passed to m_iPixel... correctly, so I hardcoded the values to 0xff in the calling function. I checked this via r, g, b and am certain that they are all set to that value, yet the canvas is black.

The funny thing is: when I enter aGraphics.setColor(Color.WHITE) or aGraphics.setColor(0xff, 0xff, 0xff) instead of the variables r, g, b it works! Even though I checked the variables to be at the same value and hard coded them earlier to 0xff. I am completely out of ideas as to what could be the issue...

EDIT:

The values were hardcoded as follows:

public void setPixelColour(int i, int j, int r, int g, int b)
{
    m_iPixelRed[i][j] = 0xff;
    m_iPixelGreen[i][j] = 0xff;
    m_iPixelBlue[i][j] = 0xff;
}

setPixelColour was called by the superclass in this method:

private void calcColour(int i, int j, int aIterations)
{
    m_cCanvas.setPixelColour(i, j, 0XFF, 0xff, 0XFF);
}

Which was in turn called by this loop.

for(int i = 0; i < iCanvasHeight; i++){
    for(int j = 0; j < iCanvasWidth; j++){
        cSum.setRe(m_cCoordPlane[i][j].getRe());
        cSum.setIm(m_cCoordPlane[i][j].getIm());
        m_iIterations[i][j] = 0;
        do{
            m_iIterations[i][j]++;
            cSum = cSum.square();
            cSum = cSum.add(m_cSummand);
            m_dAbsSqValues[i][j] = cSum.getAbsSq();
        }while((m_iIterations[i][j] < MAXITER) && (m_dAbsSqValues[i][j] < m_iDivergThresh));
        this.calcColour(i, j, m_iIterations[i][j]);
        m_cMsgIter = "x = " + i + " , y = " + j;
        this.repaint();
    }
}

I checked made sure that this loop is definitely completed. I checked the values again using the debugger right before setColor(). Since I don't trust the debugger (out of experience) I checked another time with the console by adding System.out.println("r = " + Integer.toString(r) + " g = " + Integer.toString(g) + " b = " + Integer.toString(b)); right before setColor().

EDIT:

This is my paint method of the JFrame:

public void paint(Graphics aGraphics) 
{
    Graphics cScreenGraphics = aGraphics;
    // render on background image
    aGraphics = m_cBackGroundImage.getGraphics();

    this.paintComponents(aGraphics);
    // drawString() calls are debug code only...
    aGraphics.setColor(Color.BLACK);
    aGraphics.drawString(m_cSMsg, 10, 450);
    aGraphics.drawString(m_cMsgIter, 10, 465);
    aGraphics.drawString(m_cMsgDivThresh, 10, 480);

    // rendering is done, draw background image to on screen graphics
    cScreenGraphics.drawImage(m_cBackGroundImage, 0, 0, null);
}

Answer 1

Not sure if posting big chunks of code in comments makes a whole lot of sense so here's my test code for you:

package test;

import javax.swing.JFrame;

public class Test 
{
    public static void main(String[] args) 
    {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        MyCanvas canvas = new MyCanvas();
        frame.add(canvas);
        frame.pack();
        frame.setVisible(true);

        for(int i = 0; i < 800; i++)
        {
            for(int j = 0; j < 600; j++)
            {
                canvas.setPixelColour(i, j, 0XFF, 0xff, 0XFF);
                canvas.repaint();
            }
        }
    }
}

And this is the MyCanvas class:

package test;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.image.BufferedImage;

public class MyCanvas extends java.awt.Canvas
{
    private BufferedImage m_cBackGroundImage;
    private int[][] m_iPixelRed, m_iPixelGreen, m_iPixelBlue;
    private int m_iWidth, m_iHeight;

    public MyCanvas()
    {
        setPreferredSize(new Dimension(800, 600));
        m_iWidth = 800;
        m_iHeight = 600;
        m_cBackGroundImage = new BufferedImage(m_iWidth, m_iHeight, BufferedImage.TYPE_INT_ARGB);     
        m_iPixelRed = new int[m_iWidth][m_iHeight];
        m_iPixelGreen = new int[m_iWidth][m_iHeight];
        m_iPixelBlue = new int[m_iWidth][m_iHeight];
    }

    public void paint(Graphics aGraphics) 
    {
        Graphics cScreenGraphics = aGraphics;

        aGraphics = m_cBackGroundImage.getGraphics();

        for(int i = 0; i < m_iWidth; i++) 
        {
            for(int j = 0; j < m_iHeight; j++) 
            {
                int r = m_iPixelRed[i][j];
                int g = m_iPixelGreen[i][j];
                int b = m_iPixelBlue[i][j];
                aGraphics.setColor(new Color(r, g, b));
                aGraphics.drawRect(i, j, 0, 0);
            }
        }

        cScreenGraphics.drawImage(m_cBackGroundImage, 1, 1, null);
    }

    public void setPixelColour(int i, int j, int r, int g, int b)
    {
        m_iPixelRed[i][j] = r;
        m_iPixelGreen[i][j] = g;
        m_iPixelBlue[i][j] = b;
    }
}

I tried staying as close to what you provided as possible (even though your naming convention is not really my kind of thing). The main changes were in the loop in the main method because I didn't need most of that code. I also obliterated the calcColor method because it simply called a different method.

Anyway, this works for me (= I get a white canvas). I also tried changing the 0xff s to (int)(Math.random() * 255) which will result in a... let's go with rainbow-colored canvas, so it seems to be working fine.