I have an SWT Canvas with some image on it. I want my user to select parts of the image by clicking, holding the left mouse button and opening a selection box by moving the mouse. As a visual feedback I want to show the selected rectangle as a transparent overlay over my image.
The problem is I have not clue how to best achieve this? Can someone give me a hint?
My answer is somehow similar to the one I gave here:
The code below should give you an idea on where to start. It basically remembers the location of a MouseDown event. Each time the mouse is then dragged, a rectangle is drawn from the starting location to the current location. Once MouseUp happens, everything stops.
public class DrawExample
{
private static boolean drag = false;
private static int startX;
private static int startY;
private static int endX;
private static int endY;
public static void main(String[] args)
{
Display display = new Display();
Shell shell = new Shell(display);
shell.setText("Drawing Example");
final Canvas canvas = new Canvas(shell, SWT.NONE);
canvas.setSize(150, 150);
canvas.setLocation(20, 20);
shell.open();
shell.setSize(200, 220);
canvas.addListener(SWT.MouseDown, new Listener() {
@Override
public void handleEvent(Event event) {
startX = event.x;
startY = event.y;
drag = true;
}
});
canvas.addListener(SWT.MouseUp, new Listener() {
@Override
public void handleEvent(Event event) {
endX = event.x;
endY = event.y;
drag = false;
canvas.redraw();
}
});
canvas.addListener(SWT.MouseMove, new Listener() {
@Override
public void handleEvent(Event event) {
if(drag)
{
endX = event.x;
endY = event.y;
canvas.redraw();
}
}
});
canvas.addListener(SWT.Paint, new Listener() {
@Override
public void handleEvent(Event event) {
if(drag)
{
GC gc = event.gc;
gc.setBackground(Display.getDefault().getSystemColor(SWT.COLOR_BLACK));
gc.setAlpha(128);
int minX = Math.min(startX, endX);
int minY = Math.min(startY, endY);
int maxX = Math.max(startX, endX);
int maxY = Math.max(startY, endY);
int width = maxX - minX;
int height = maxY - minY;
gc.fillRectangle(minX, minY, width, height);
}
}
});
while (!shell.isDisposed())
{
if (!display.readAndDispatch())
display.sleep();
}
display.dispose();
}
}
It looks like this:
There is another approach that native platform provides to do this. Use SWT org.eclipse.swt.widgets.Tracker
How do I make it possible to resize a composite by dragging the corner
