Re: Compositing to custom view in Cocoa

FROM : George Orthwein
DATE : Fri Jun 30 17:17:59 2006

On Jun 30, 2006, at 10:36 AM, Kenny Millar wrote:
> Because I need to change the foreground colour too, and every 
> location on
> the 'screen' can have a different forground/background colour.


It would take two operations. You'd composite the text with 
transparent background with a solid fill color as source, using 
CompositeSourceIn. That colorizes the text and leaves the 
transparency. Then you'd draw that over the background color. At 
least, I think that should work. :)

If you can't add transparency, I just discovered -
colorizeByMappingGray:toColor:blackMapping:whiteMapping. It kinda 
works for me but for some reason the white areas are using the gray 
color instead of the specified white color. But I did end up with 
custom back/foreground colors.

I'm surprised there is not an NSImage method for using a grayscale 
image as a mask. Half the messages in the archives asking about this 
topic reference CompositeSourceIn, but I see now that that will only 
work if you already have some transparency. There do seem to be some 
Quartz methods though:
http://developer.apple.com/documentation/GraphicsImaging/Conceptual/
drawingwithquartz2d/dq_images/chapter_12_section_6.html

Looks like a good candidate for an NSBitmapImageRef category. :) 
(though I don't actually know how difficult using the quartz calls 
would be...)

George