I have to wonder why you're going to all this trouble when
UIGraphicsBeginImageContext exists. What exactly are you planning on
doing, ultimately, with this context? And why do you need to clear the
entire thing after you've drawn into it? m.
On Mon, 4 Oct 2010 11:34:23 -0700, Rainer Standke <li...@standke.com> said:
>This is indeed outside of -drawRect, and it's a context I create myself,
>like so:
>
> // returns a new 'abstract' graphics context to draw in:
> CGContextRef context = NULL;
> CGColorSpaceRef colorSpace;
> void * bitmapData;
> int bitmapByteCount;
> int bitmapBytesPerRow;
>
> bitmapBytesPerRow = (pixelsWide * 4);
> bitmapByteCount = (bitmapBytesPerRow * pixelsHigh);
>
> colorSpace = CGColorSpaceCreateDeviceRGB();
> bitmapData = malloc( bitmapByteCount );
> if (bitmapData == NULL)
> {
> fprintf (stderr, "Memory not allocated!");
> return NULL;
> }
> context = CGBitmapContextCreate (bitmapData,
> pixelsWide,
> pixelsHigh,
> 8, // bits per component
> bitmapBytesPerRow,
> colorSpace,
> kCGImageAlphaPremultipliedLast);
> if (context== NULL)
> {
> free (bitmapData);
> fprintf (stderr, "Context not created!");
> return NULL;
> }
> CGColorSpaceRelease( colorSpace );
>
> CGContextSetAllowsAntialiasing(context, YES);
> CGContextSetShouldAntialias(context, YES);
>
> return context;
>
>
>
>
>Rainer
>
>
>On Oct 4, 2010, at 11:15 , David Duncan wrote:
>
>> On Oct 4, 2010, at 11:04 AM, Rainer Standke wrote:
>>
>>> wondering how to clear a context. I'm using this:
>>>
>>> CGContextClearRect(context, drawingRect);
>>>
>>> But yet, afetr I do that, and then start to draw something new, I get
>>>remnants of the previous content of the context.
>>
>>
>> Where are you calling this? About the only thing I know of that might
>>cause this is trying to call UIGraphicsGetCurrentContext() from outside
>>of -drawRect: (in which case unless you've pushed or started your own
>>context you get back NULL, which CG ignores).
>> --
>> David Duncan
>>
>
>
>
>
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