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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