setDefaults has costs involved and those can vary from filter to
filter (especially in terms of elaborate 3rd party image units that
might do computation to determine defaults). So you don't want to tax
every filter creation with it, therefore it is an opt-in model.
But your concern is still valuable feedback for us.
To use +filterWithName:keysAndValues:, I have to be careful to
include certain "required" keys before I chain the filters, or I
get runtime errors like:
An uncaught exception was raised
CIUnsharpMask: sharpen: nil value for argument #2 (scale)
*** Uncaught exception: <CIKernelNilArgument> CIUnsharpMask:
sharpen: nil value for argument #2 (scale)
Program has exited due to signal 5 (SIGTRAP).
In this case, the CIUnsharpMask filter requires "inputImage" and
"inputIntensity" but not "inputRadius" (I can leave it out). Who is
to know? There are many like this. How can I know which keys are
required?
If CIFilter +filterWithName:keysAndValues: can invoke -setDefaults,
then it is much easier to set up a chain of filters, since I only
need to use this one method, and I don't need to supply values for
all of the keys at this point.
Roland
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