Mouse Panning

JGo
1

Hello,

I need to implement mouse based panning support to my JGoView (the ability to drag the canvas around). This seems like a fairly common application feature— does support for this exist in JGo, or in any example code?

-Justin

2
This requires defining an additional mouse state for the JGoView.
Basically, in your subclass of JGoView, define:
public static final int MouseStatePanning = MouseStateLast+1; private Point myLastViewPoint = null;
Override JGoView methods:
public boolean doMouseDown(int modifiers, Point dc, Point vc) {
if (getState() == MouseStatePanning) {
myLastViewPoint = new Point(vc.x, vc.y);
return true;
} else {
return super.doMouseDown(modifiers, dc, vc);
}
}
public boolean doMouseMove(int modifiers, Point dc, Point vc) {
if (getState() == MouseStatePanning) {
if (myLastViewPoint != null) {
Point pos = getViewPosition();
Dimension delta = new Dimension(myLastViewPoint.x-vc.x, myLastViewPoint.y-vc.y);
convertViewToDoc(delta);
myLastViewPoint.x = vc.x;
myLastViewPoint.y = vc.y;
setViewPosition(pos.x+delta.width, pos.y+delta.height);
}
return true;
} else {
return super.doMouseMove(modifiers, dc, vc);
}
}
public boolean doMouseUp(int modifiers, Point dc, Point vc) {
if (getState() == MouseStatePanning) {
myLastViewPoint = null;
return false;
} else {
return super.doMouseUp(modifiers, dc, vc);
}
}
public void doCancelMouse() {
if (getState() == MouseStatePanning) {
setState(MouseStateNone);
} else {
super.doCancelMouse();
}
}
Then your command to put your view into manual panning mode is just a call to
JGoView.setState(MouseStatePanning). The actual panning doesn't start until
a mouse down has happened, since doMouseMove is a no-op while myLastViewPoint is null.
You'll probably want to call setCursor in the appropriate places, and maybe
other fanciness.
3

Thanks-- this works great. I added some code to trigger the panning mode with the shift key and change the cursor:

    @Override
    public void keyPressed(KeyEvent evt) {
        if (evt.isShiftDown()) {
            if (getState() != MouseStatePanning) {
                setState(MouseStatePanning);
                setCursor(Cursor.getPredefinedCursor(Cursor.MOVE_CURSOR));
            }
        }
        super.keyPressed(evt);
    }

    @Override
    public void keyReleased(KeyEvent evt) {
        if (!evt.isShiftDown()) {
            if (getState() == MouseStatePanning) {
                setState(MouseStateNone);
                setCursor(getDefaultCursor());
            }
        }
        super.keyReleased(evt);
    }

However, during the actual dragging the cursor changes temporarily to the selection cursor. I’m having trouble determining what code in JGoView.java is causing this cursor change, as setCursor / setCursorType is only called in a few places…

4

Perhaps you need to call JGoView.setDefaultCursor.

5

Did anyone ever get a fix for this?

I have the same problem right now with the cursor changing to the selection cursor when the mouse moves, regardless of what I set the cursor to.
I have tried view.setCursor(), view.getCanvas().setCursor, and view.setDefaultCursor()
Many thanks for any input!
6

The cursor is being changed by the drag/drop mechanism. You can avoid that by overriding JGoView.initializeDragDropHandling() as follows:

public void initializeDragDropHandling() {
super.initializeDragDropHandling();
setDragDropEnabled(false);
}
Of course this will disable dragging from one JGoView to another, but this may not be an issue for you.
7

Thanks, Scott.

This does work, but creates another problem for me, since I am trying to use right-click drag to pan with the mouse. Now, I get my cursor correct, but I always get my popup menu after dragging.
I'll pursue it more later to see about getting it all fixed up :).
Many thanks for the tip!
Cheers,
Brian