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Re: CopyBits and dual monitor configration

Locking the pixels in a pixmap is *always* mandatory before passing
that pixmap to CopyBits. The reason is that the call to CopyBits can
move memory - including the actual pixels in the pixmaps.

See the sample listing at:

http://developer.apple.com/documentation/mac/QuickDraw/QuickDraw-304.html#MARKER-9-27

Michael
Orbital Launch & Lift, Inc.
The MacOS X setuid Helper Tool Experts
http://www.orbitallaunch.com

At 5:38 PM -0700 7/29/04, John Stiles wrote:
>On Jul 29, 2004, at 5:21 PM, OL&L Lists wrote:
>
>> I don't think that's true. Any call that modifies the port's bits
>> directly should always be bracketed by lock/unlock calls:
>>
>> http://developer.apple.com/documentation/Carbon/Reference/
>> QuickDraw_Ref/qdref_main/function_group_3.html#//apple_ref/c/func/
>> LockPortBits
>>
>> "If you're writing code that reads or modifies the port bits
>> directly, you should bracket your code with calls to this function
>> and UnlockPortBits."
>
>"Modifying the port bits directly" means assigning to them without
>using QuickDraw, i.e. via a custom blitter. Any QuickDraw call will do
>the right thing without an explicit need to lock and unlock.
>
>You may see a performance benefit if you manually lock, since QuickDraw
>will lock and unlock between every single operation (it doesn't know
>how many things you plan on doing with the port). But unless you are
>by-hand overwriting pixels, you do not need to concern yourself with
>this.
>
>> From experience it sounds to me more like you have a SetPort problem.
>
>I agree; IMO the OP's problem is probably caused by not setting the
>port properly before the CopyBits...
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References: 
 >Re: CopyBits and dual monitor configration (From: John Stiles <email@hidden>)



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