Ah, so your problem is that not every CG blend mode is available as an
NSCompositingOperation? If you would, please file a quick bug
mentioning that you needed this.
If you're running on 10.6, you can use -[NSImage
CGImageForProposedRect:context:hints:] to get a CGImage, then draw the
CGImage with your blend mode. See the AppKit relnotes for details, but
that's likely to be efficient. If that method isn't available, you can
get the same end effect by taking a destination CGContext, setting the
blend mode to darken, starting a transparency layer, drawing the
NSImage in copy or source over mode, and ending the transparency
layer. The layers contents are composited to the context in darken
mode. Repeat for each NSImage. Perf-wise, this is like drawing each
image once in copy mode and once in darken mode. Copy mode is
vectorized, darken mode isn't, so I would expect to see most of your
time in CGContextEndTransparencyLayer for images of reasonable size.
-Ken
Sent from my iPhone, so be forgiving.
On Apr 18, 2010, at 7:14 PM, Izak van Langevelde <eezac...@xs4all.nl>
wrote:
I need to combine a number of NSImages such that each pixel of the
result is the darkest of the corresponding pixels of the NSImages.
Blend mode 'darken' does exactly what I need to, but I'm clueless
about how to efficiently apply blend modes to NSImages.
An alternative is to use an NSCompositingOperation, but the best
candidate NSCompositePlusDarker is not exactly what I need.
I could convert my NSImage to a bitmap and do my thing, but fear a
performance hit.
Any suggestions?
Thanks,
Izak
---
Grinnikend door het leven...
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