Re: How to get rid of blinking?
Re: How to get rid of blinking?
- Subject: Re: How to get rid of blinking?
- From: Nick <email@hidden>
- Date: Wed, 19 Oct 2011 22:50:57 +0300
Thank you
2011/10/19 Fritz Anderson <email@hidden>
> On 19 Oct 2011, at 12:41 PM, Nick wrote:
>
> > Could you advice me how to get rid of blinking in the following code?
> > This is an NSView's subclass, I am trying to draw a rectangle for zooming
> > (theoretically a user is supposed to be able to zoom in a piece of a
> view,
> > by selecting a rectangle area to zoom.
> > The problem is that when the mouse is being dragged, the rectangle that's
> > being drawn is blinking.
> > What would be the write approach to make it behave like other software
> where
> > a user can select things with a rectangle?
>
> You're fighting the framework. Calling -display yourself or drawing outside
> of drawRect: are powerful code smells. This is a tangle:
>
> =====
> [self display];
> // Forces an immediate call to drawRect:.
>
> [self lockFocus];
> [self drawRectUsingTwoPoints:lastMouseDownPos:locationOnCanvas];
> [self unlockFocus];
> // Draw over what drawRect: drew.
>
> [self displayIfNeeded]; //show the currect "rectangle"
> // Force _another_ drawRect:, again without drawing the selection
> rectangle.
> // If your first drawRect:, via -display, cleared your selection
> rectangle, this
> // repeated call to drawRect: will erase it _again_.
> =====
>
> If you're using mouseUp/Dragged/Down methods, you'll be returning to the
> event loop, and thus to the built-in redrawing through drawRect:, anyway.
> And, Quartz will schedule it so everything is coalesced and won't flicker.
>
> In your tracking methods, just save the selection rectangle in an instance
> variable (which can be NSZeroRect if you don't have a selection). When the
> rectangle changes, send -setNeedsDisplay (not displayIfNeeded) to the view
> and let the scheduling take care of itself. drawRect: can check for a
> non-NSZeroRect selection, and you can draw the rectangle if there's one to
> draw.
>
> — F
>
>
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