Each view draw's into the window's graphic context. When focus is
locked on a view the window's context is clipped and translated to the
view so that drawing is limited to just the view's bounds. Basically
all views in a window generally use the window's context (OpenGL views
and whatnot have their own context). To get the context for the
window use NSGraphicsContext's graphicsContextWithWindow: or
NSWindow's graphicsContext to get the Cocoa context, then use the
graphicsPort method to get a CGContextRef from it (docs say it returns
a void*, but it is a CGContextRef).
Also, I believe a window has a different graphics context for each
thread that draws to it, so try and draw from the thread you got the
CGContextRef from. Probably just keep drawing within the main thread
to be safe.
You might also look into CoreImage (CIImage, CIContext) if you need to
support 10.4; many of the new CGContext blend modes are 10.5 only.
On Apr 23, 2008, at 1:13 AM, Ross Oliver wrote:
I haven't used core graphics before and I'm looking to create an
overlay blend mode effect with two images.
I have a NSImageView with the image set to an NSImage. What are the
general steps I would need to take to draw another image on top of
it and set it as an overlay?
The documentation Apple has is long and confusing - I can't seem to
figure out how to even get a CGContextRef for the NSImageView.
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