On Jan 7, 2010, at 5:36 PM, David Blanton wrote: > CGColorSpaceRef colorSpace; > colorSpace = CGColorSpaceCreateWithName(kCGColorSpaceGenericRGB); > CGDataProviderRef provider = CGDataProviderCreateWithData > (NULL,m_bitmap.m_array, 4*m_bitmap.m_pixelsx*m_bitmap.m_pixelsy, NULL); > CGImageRelease(m_CGImageRef); > m_CGImageRef = CGImageCreate(m_bitmap.m_pixelsx, m_bitmap.m_pixelsy, 8, > 32, 4*m_bitmap.m_pixelsx, colorSpace, > kCGImageAlphaNoneSkipFirst|kCGBitmapByteOrder32Host, provider, NULL,YES, > kCGRenderingIntentDefault); > CGImageRetain(m_CGImageRef); > CGColorSpaceRelease(colorSpace); > CGDataProviderRelease(provider); > > Clearly I have kicked NSBitMapImageRep under the bus as the above gives what > I am looking for. > > The performance issue comes from the fact the user will be dragging this > bitmap around so I a regenerating m_bitmap.m_array constantly.
The specific performance issue with using CGBitmapContextCreate() with CGBitmapContextCreateImage() to wrap a buffer of data is that in order to preserve the semantics of a CGImageRef, CGBitmapContextCreateImage() needs to mark the buffer pointed to by the bitmap context as copy-on-write. This requires a call into the kernel, which is a relatively expensive process. This process is typically cheaper than actually copying the bytes around, but since you aren't actually using the context it is more expensive than going the direct route. However, since creating an image directly via CGImageCreate() is nearly identical to creating a bitmap context, it is the preferred solution since it avoids a call into the kernel. The only significant difference is the need to create a data provider, but doing that is straightforward. In the end, it is about the same number of lines of code to create the image directly, and you avoid the call into the kernel. -- David Duncan Apple DTS Animation and Printing _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
