Question

Have the following code:

image = new Image(display, imageData);
offScreenImageGC.drawImage(image, 0, 0, imageData.width, imageData.height, imageData.x, imageData.y, imageData.width, imageData.height);
/* Draw the off-screen image to the shell. */
shellGC.drawImage(offScreenImage, 0, 0);

… after executing the bottom instruction: shellGC.drawImage(offScreenImage, 0, 0); sometimes I get the image visible on the shellGC component, sometimes – not. I get it visible only when I “slow down” the execution of the program , for example when I am in debug mode. But when it runs fast – it does not show. I want it forcefully shown, flushed or whatever you name it, is it possible ?

Let me clarify that what I want to achieve is to implement an animation which is frame based, but yet to be able to play it double buffered, able to stop it, show only particular single frame paused, and etc things…

Thank you.

Answer 1

It came out that this is the ONLY SAFE way to double buffer with SWT:

canvas.addPaintListener(new PaintListener() {
              public void paintControl(PaintEvent event) {
                 //Obtain the next frame
                ImageData imageData = imageDataArray[iad.imageNumber];
                Image imageFrame = new Image(display, imageData);

                // Create the image to fill the canvas
                Image image = new Image(display, canvas.getBounds());

                // Set up the offscreen gc
                GC gcImage = new GC(image);

                //Draw the image offscreen
                gcImage.setBackground(event.gc.getBackground());
                gcImage.drawImage(imageFrame, 0, 0);

                // Draw the offscreen buffer to the screen
                event.gc.drawImage(image, 0, 0);

                imageFrame.dispose();
                image.dispose();
                gcImage.dispose();
              }
            });

…. by using this method ONLY for doublebuffering there is guaranteed crossplatform equal runtime behaviour, and the unpredictable buffer behaviour is also gone.