Apologies for the cross posting from quartz-dev. But it seems these days that
it is hard to work out which forum, lists/devforum and then which of the
discussions to then post.
I've been playing with creating a core image filter for OS X. I've got simple
chroma key filter working as I would like, except for two issues. The first
issue is a compile warning which if I ignore doesn't stop the filter from
working. But I'd still like it resolved even if it is only for me to understand
what is going on, or perhaps that it highlights something that I'm doing wrong
but non-critical.
The filter is defined like so in the header:
@interface YVSChromaKeyFilter : CIFilter
Because I'm currently using the filter in a simple stand alone command line
tool and I want to keep this option as a use for the filter I'm not packaging
the filter up into a image unit as the recommended way to distribute image
filters by apple so I'm using the alternate method which uses the
registerFilterName method called from the filter's class initialize method:
@implementation YVSChromaKeyFilter
+(void)initialize
{
if (self == [YVSChromaKeyFilter class])
{
NSArray *kernels = [CIKernel kernelsWithString:YVSChromaKeyFilterString];
chromaKeyKernel = kernels[0];
[CIFilter registerFilterName:@"YVSChromaKeyFilter"
constructor:(id<CIFilterConstructor>)self
classAttributes:@{
kCIAttributeFilterDisplayName : @"Simple Chroma Key.",
kCIAttributeFilterCategories : @[
kCICategoryColorAdjustment, kCICategoryVideo,
kCICategoryStillImage, kCICategoryInterlaced,
kCICategoryNonSquarePixels]
}
];
}
}
+(CIFilter *)filterWithName:(NSString *)name
{
CIFilter *filter;
filter = [[YVSChromaKeyFilter alloc] init];
return filter;
}
Note the cast in the constructor: option of the registerFilterName method, this
was done to remove the compiler warning but really should not be there. I tried
adding the protocol to the YVSChromaKeyFilter interface but that made no
difference. My filter gets created correctly when I set things up as above and
do:
CIFilter *filter = [CIFilter filterWithName:@"YVSChromaKeyFilter"];
Now the protocol CIFilterConstructor interface is as follows:
@protocol CIFilterConstructor
- (CIFilter *)filterWithName:(NSString *)name;
@end
Which confuses me since I have to implement a class method filterWithName not
an object method.
As I said, the filter works and does what I want but I'm missing something here
that I'd like clarified and hopefully resolve things in a way that the ugly
cast can be removed.
I'll put the second issue into a new e-mail as I think putting it here now will
just add confusion.
Kevin
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