Re: GNUstep slowness while drawing

[Fred Kiefer]

Andreas Höschler wrote:
> Hi all,
>
> I have a view subclass with
>
> - (void)mouseDown:(NSEvent *)theEvent
> {
>    NSPoint locA = [self convertPoint:[theEvent locationInWindow] 
> fromView:nil];
>    BOOL shiftPressed = (([theEvent modifierFlags] & NSShiftKeyMask) > 0);
>    BOOL keepOn = YES;
>    BOOL hasDragged = NO;
>
>    while (keepOn)
>      {
>       theEvent = [[self window] nextEventMatchingMask:NSLeftMouseUpMask 
> | NSLeftMouseDraggedMask];
>       switch ([theEvent type])
>         {
>          case NSLeftMouseDragged:
>            {
>               NSPoint locB = [self convertPoint:[theEvent 
> locationInWindow] fromView:nil];
>               NSSize offset =  NSMakeSize(locB.x - locA.x, locB.y - 
> locA.y);
>               NSRect oldRect = _selectionRect;
>               _selectionRect.origin = locA;
>               if (offset.width < 0)
>                 {
>                  _selectionRect.origin.x = locB.x;
>                  offset.width = -offset.width;
>                 }
>               if (offset.height < 0)
>                 {
>                  _selectionRect.origin.y = locB.y;
>                  offset.height = -offset.height;
>                 }
>               _selectionRect.size = offset;
>               _selecting = YES;
>               [self setNeedsDisplayInRect:NSUnionRect(_selectionRect, 
> oldRect)];
>               hasDragged = YES;
>            }
>             break;
>
>          case NSLeftMouseUp:
>            {
>               keepOn = NO;
>            }
>             break;
>
>          default:
>             break;
>         }
>      }
> }
>
> - (void)drawRect:(NSRect)rect
> {
>    [super drawRect:rect];
>    if (_selecting)
>      {
>       [[NSColor grayColor] set];
>       NSFrameRect(_selectionRect);
>      }
> }
>
> This draws a rectangle following the mouse until the user releases the 
> mouse button. On MacOSX the rectangle follows the mouse instantly. Under 
> GNUstep I see a significant delay. Dragging rectangles makes no fun 
> there. Any idea why this is so slow? This of course has nothing to do 
> with rectangles in special but with slow drawing code in general. In my 
> app I want to drag objects around with the mouse. This works under 
> GNUstep and MacOX but on GNustep it is almost too slow to be usable. Is 
> this a known (may be even already improved) issue? My GNUstep tree is 
> already a year old. :-)

Most likely the slow drawing speed you see in GNUstep has nothing to do 
with the drawing itself, but with the event handling in GNUstep. The 
window will just not get a chance to redraw itself.
One possible reason for this may be that in
[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] we 
handle an expiration date of nil different from Cocoa. There distantPast 
is used while we use distantFuture, resulting in the loop to wait until 
the next event happens.

As I am no expert in this area, I would like to get some comments from 
other developers before changing this code. That change may result in 
the need to adopt a lot of places that rely on the old behaviour.