Re: transparent icons

[Fred Kiefer]

Stefan Boehringer wrote:
> 
> As a sidenote Willem Rein Oudshoorn pointed out in private mail that 
> [compositeToPoint:fromRect:operation:fraction:] is not equivalent to either 
> of the DPS operators DPScomposite or DPSdissolve. This method is new to 
> MacOSX. Is it just a wrapper for a sequential call of the above operators or 
> does it do anything new?
> 
Yes, this is new, but I don't think it does a sequential call to the
above operators. It will rather use the alpha value given by the
fraction instead of the alpha values from the original images. But this
is also only a guess.

> Fred probably means pixelwise blending by the "simple and slow 
> implementation" (do you?). Maybe such a trivial implementation may be enough 
> for dissolving such tiny images as icons.
> 
Yes again. This is not hard to implement.

> 
> PS: Somewhere deep back in my memory, I remember that compositing (and 
> dissolving as well I guess) was something odd in that scaling, rotation and 
> flipping status of a destination view was *not* respected by the operator. 
> This was (again I guess) for efficiency reasons to allow a pixel by pixel 
> transfer from image to framebuffer without having to do scaling/antialiasing 
> and so on. If you wanted such a thing you had to scale/flip/rotate the image 
> first and then do the compositing. Maybe this has changed in MacOSX...
> 

And once more you are right. Composing and dissolving does not do any
scaling, etc. and this is still the same in MacOSX. But there are new
methods on NSImage that will do this. The are called
drawAtPoint:fromRect:operation:fraction: and
drawInRect:fromRect:operation:fraction: