The following example is from Gorm but it is actually the same in
GWorkspace:
while ([e type] != NSLeftMouseUp)
{
p = [self convertPoint: [e locationInWindow] fromView: nil];
x = (p.x >= oldp.x) ? oldp.x : p.x;
y = (p.y >= oldp.y) ? oldp.y : p.y;
w = max(p.x, oldp.x) - min(p.x, oldp.x);
w = (w == 0) ? 1 : w;
h = max(p.y, oldp.y) - min(p.y, oldp.y);
h = (h == 0) ? 1 : h;
r = NSMakeRect(x, y, w, h);
if (NSEqualRects(oldRect, NSZeroRect) == NO)
{
[verticalImage
compositeToPoint: NSMakePoint(NSMinX(oldRect),
NSMinY(oldRect))
fromRect: NSMakeRect(0.0, 0.0, 1.0, oldRect.size.height)
operation: NSCompositeCopy];
[verticalImage
compositeToPoint: NSMakePoint(NSMaxX(oldRect)-1,
NSMinY(oldRect))
fromRect: NSMakeRect(1.0, 0.0, 1.0, oldRect.size.height)
operation: NSCompositeCopy];
[horizontalImage
compositeToPoint: NSMakePoint(NSMinX(oldRect),
NSMinY(oldRect))
fromRect: NSMakeRect(0.0, 0.0, oldRect.size.width, 1.0)
operation: NSCompositeCopy];
[horizontalImage
compositeToPoint: NSMakePoint(NSMinX(oldRect),
NSMaxY(oldRect)-1)
fromRect: NSMakeRect(0.0, 1.0, oldRect.size.width, 1.0)
operation: NSCompositeCopy];
}
{
NSRect wr;
wr = [self convertRect: r
toView: nil];
[verticalImage lockFocus];
NSCopyBits([[self window] gState],
NSMakeRect(NSMinX(wr), NSMinY(wr),
1.0, r.size.height),
NSMakePoint(0.0, 0.0));
NSCopyBits([[self window] gState],
NSMakeRect(NSMaxX(wr)-1, NSMinY(wr),
1.0, r.size.height),
NSMakePoint(1.0, 0.0));
[verticalImage unlockFocus];
[horizontalImage lockFocus];
NSCopyBits([[self window] gState],
NSMakeRect(NSMinX(wr), NSMinY(wr),
r.size.width, 1.0),
NSMakePoint(0.0, 0.0));
NSCopyBits([[self window] gState],
NSMakeRect(NSMinX(wr), NSMaxY(wr)-1,
r.size.width, 1.0),
NSMakePoint(0.0, 1.0));
[horizontalImage unlockFocus];
}
[[NSColor darkGrayColor] set];
NSFrameRect(r);
oldRect = r;
[[self window] enableFlushWindow];
[[self window] flushWindow];
[[self window] disableFlushWindow];
e = [NSApp nextEventMatchingMask: eventMask
untilDate: future
inMode: NSEventTrackingRunLoopMode
dequeue: YES];
}
