How to save transperant gif

Question

I am building a generic graph package and I wanted to capture the graph (image) and save it into a GIF file with a transperent background.
I have been struggling with the transperant part for a whole day, but now I finally found how to do it and I just wanted to share this knowledge with the rest of you.
<b>1.) Generate the Graph</b>
I created two new methods BufferedImage getImage() and void drawImage( Graphics2D )
<pre>
public BufferedImage getImage( int width, int height ) {
BufferedImage bufImage = new BufferedImage( width, height, BufferedImage.TYPE_4BYTE_ABGR ); //Create a new BufferedImage
Graphics2D graphics2D = bufImage.createGraphics(); //Creates a Graphics2D, which can be used to draw into this BufferedImage
graphics2D.setColor( new Color( 255, 255, 255, 0 ) ); // The last int is the alpha value and 0 will make the Color transperent
graphics2D.fillRect( 0, 0, width, height ); // Fill a Rectangle with the same size as the image with the transparent color
drawImage( graphics2D ); //Draw the actual graph on the transparent Rectangle
return bufImage; //Return the BufferedImage
</pre>
<pre>
public void drawImage( Graphics2D g ) {
drawGraph( g ); //Draws the axis
putValues( g ); //Draws the actual values/graph
</pre>
<b>2.) Paint the Graph in you Component (Panel/JPanel, Frame/JFrame, etc)</b>
<pre>
public void paint( Graphics g ) {
Dimension bounds = this.getSize(); //Get the Dimension/Size of the Component
g.drawImage( getBufImage( bounds.width, bounds.height ), 0, 0, this ); //Get the BufferedImage and draw it on the Components Graphics Object
</pre>
<b>3.) Save the Graph into a GIF file</b>
<b>3.1. Download the Acme package to be able to save to GIF</b> (You will only need the GifEncoder, ImageEncoder and IntHashtable).
<b>3.2. Save to GIF</b>
<pre>
import Acme.*;
import Acme.JPM.Encoders.*;
public void saveGIF( String filename, int width, int height ) {
BufferedImage bufImage = getBufImage(); //Get the BufferedImage with the Graph drawn on a transparent Rectangle
Graphics2D graphics2D = bufImage.createGraphics();Creates a Graphics2D, which can be used to draw into this BufferedImage
graphics2D.setRenderingHint( RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR ); //Sets the value of a single preference for the rendering algorithms
try {
GifEncoder gifcoder = new GifEncoder(bufImage, new BufferedOutputStream( new FileOutputStream( fileName + ".gif" ) ) ); //Create a new GIFEncoder for the BufferedImage and a OutputStream
gifcoder.encode(); //Write the image into GIF
catch( FileNotFoundException fnfe ) {
System.err.println( "error: MGraph.saveImage( String ): " + fnfe );
catch( IOException ioe ) {
System.err.println( "error: MGraph.saveImage( String ): " + ioe );
</pre>
That's it! I hope this will be helpful and save you some time.
/Max

Answer 1

I am also going to start to build some form of graphic plot toolkit for a project in my university. I would be great to know how you have defined your API and how the output of the graphs look like. If you are willing to share that?
Regards,
Peter.