Turning images transparent

Here are 3 methods for making an actor’s image to have a transparent background.

All require the following import statement:

import java.awt.Color;

And turnTransparent3() requires:

import java.util.List;

---

/**
 * This method removes the color Color.WHITE
 * from the actor's image.
 */
private void turnTransparent()
{
    GreenfootImage img = getImage();
    Color transparent = new Color(0, 0, 0, 0);
    for(int x = 0; x < img.getWidth(); x++)
    {
        for(int y = 0; y < img.getHeight(); y++)
        {
            if(img.getColorAt(x, y).equals(Color.WHITE))
                img.setColorAt(x, y, transparent);
        }
    }
}

---

/**
 * This method removes the all whitish
 * colors from the actor's image.
 */
private void turnTransparent2()
{
    int range = 10; //Should be in the range 0-255.
    GreenfootImage img = getImage();
    Color transparent = new Color(0, 0, 0, 0);
    for(int x = 0; x < img.getWidth(); x++)
    {
        for(int y = 0; y < img.getHeight(); y++)
        {
            Color color = img.getColorAt(x, y);
            if(color.getRed()   > 255 - range
            && color.getGreen() > 255 - range
            && color.getBlue()  > 255 - range)
                img.setColorAt(x, y, transparent);
        }
    }
}

---

/**
 * This method method finds the background
 * color and removes it from the actor's image.
 */
private void turnTransparent3()
{
    GreenfootImage img = getImage();
    Color transparent = new Color(0, 0, 0, 0);
    List<Color> colors = new ArrayList<Color>();
    List<Integer> frequencys = new ArrayList<Integer>();
    for(int x = 0; x < img.getWidth(); x++)
    {
        for(int y = 0; y < img.getHeight(); y++)
        {
            Color thisColor = img.getColorAt(x, y);
            int matchPos = colors.indexOf(thisColor);
            if(matchPos != -1)
            {
                frequencys.set(matchPos, frequencys.get(matchPos) + 1);
            }
            else
            {
                colors.add(thisColor);
                frequencys.add(1);
            }
        }
    }
    int maxFreq = 0,
        maxPos = 0;
    for(int i = 0; i < frequencys.size(); i++)
    {
        if(frequencys.get(i) > maxFreq)
        {
            maxFreq = frequencys.get(i);
            maxPos = i;
        }
    }
    Color bgColor = colors.get(maxPos);
    for(int x = 0; x < img.getWidth(); x++)
        for(int y = 0; y < img.getHeight(); y++)
            if(img.getColorAt(x, y).equals(bgColor))
                img.setColorAt(x, y, transparent);
}

Background resizing

This is a very simple method, but one that you might not think to do – I know at least from my point of view in many of my early scenario’s I resized the actual image file that I was using for a background to whatever my world size was. I found later that when I was changing the world size I would have to resize the image file again – after a while this got to be a time consuming process and I was sure there was a better way.. hence why I made this method:

void resizeBackground()
{
    getBackground().scale(getWidth(), getHeight());
}

Place a call to it in your world’s constructor.