Re: Lock/unlock focus does not draw image in Snow Leopard

Hi Michael,
> I do not understand the reason for this change in the behavior of
lockFocus -- if it was intentional or is a bug.

Please always file a bug if you are asking this question.

I think this arises from your NSCustomImageRep having size NSZeroSize.  When
the draw selector is called, the region to be drawn into is {NSZeroPoint,
[customRep size]}.  That doesn't make sense when the custom rep's size is
NSZeroSize.

The behavior change arises because NSImage used to end up doing

if ([rep size] is NSZeroSize]) [rep setSize:[self size]];

So please file a bug.

-Ken
Cocoa Frameworks

On Fri, Aug 28, 2009 at 7:26 PM, Michael McCulloch
<[email protected]>wrote:

>
> On Aug 28, 2009, at 9:38 PM, I wrote:
>
>  I have found that the following code works fine pre-Snow Leopard to draw
>> the contents of an image:
>>
>> myImage = [[NSImage alloc] initWithSize:aSize];
>> [myImage addRepresentation:[[[NSCustomImageRep alloc]
>>        initWithDrawSelector:@selector(drawMyImage:) delegate:self]
>> autorelease]];
>> [myImage lockFocus];
>> [myImage unlockFocus];
>>
>> Apparently the above worked fine since the lock/unlock focus triggered the
>> call of the drawMyImage selector (exactly how is unknown).
>>
>> However, in Snow Leopard this does not work. The draw selector is NOT
>> called. The code has to be changed to:
>>
>> myImage = [[NSImage alloc] initWithSize:aSize];
>> myImageRep = [[[NSCustomImageRep alloc] initWithDrawSelector:@selector(drawMyImage:)
>> delegate:self] autorelease];
>> [myImage addRepresentation:myImageRep];
>> [myImage lockFocus];
>> [myImageRep draw];
>> [myImage unlockFocus];
>>
>> In Snow Leopard the draw has to be explicitly called. Why the change?
>>
>> Another question: Since I do not know what the details of the
>> implementations of lockFocus and unlockFocus are on any OS X version, if I
>> now go with the Snow Leopard code for all OS X versions, does the explicit
>> [myImageRep draw] cause pre-Snow Leopard versions to draw my image TWICE?
>>
>
> My initial investigations indicate that on pre-Snow Leopard machines, the
> [myImage lockFocus] call initiates the draw selector. It does NOT do so on
> Snow Leopard.
>
> Therefore, I apparently have to make the [myImageRep draw] specific to Snow
> Leopard or else I will draw the image twice on earlier OS X versions.
>
> I do not understand the reason for this change in the behavior of lockFocus
> -- if it was intentional or is a bug. Seems like this could bite a lot of
> folks.
>
>
> ---
> Michael McCulloch
>
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