Apply a CIFilter background filter when host window is transparent

Question

I want to replicate the background of dock Stacks in grid and list mode. The background is translucent black with a blur effect:

Example of dock stack in grid mode http://www.thecustommac.com/wp-content/uploads/2009/09/stack-highlight.jpg

The problem is that [CALayer backgroundFilters] only applies to content in the window, the filters are not applied to content in other windows. Here's my code:

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification 
{
    //make window transparent
    self.window.backgroundColor = [NSColor clearColor];
    [self.window setOpaque:NO];
    [self.window setHasShadow:NO];
    [self.window setStyleMask:NSBorderlessWindowMask];


    //make the content view layer hosting
    CALayer *rootLayer = [CALayer layer];
    [[self.window contentView] setLayer:rootLayer];
    [[self.window contentView] setWantsLayer:YES];


    //blur the background contents - NOT WORKING!
    [rootLayer setBackgroundColor:CGColorCreateGenericGray(0.0, .716)];

    CIFilter *blurFilter = [CIFilter filterWithName:@"CIGaussianBlur"];
    [blurFilter setDefaults];
    [rootLayer setBackgroundFilters:[NSArray arrayWithObject: blurFilter]];
}

I can't think of how else to achieve this effect. (I've taken a look at the Display Services to see if there are any useful functions but I can't see any.)

Any ideas?

Answer 1

There is private API available this. Here is sample code by Rob Keniger:

In 10.5 you can add any core image filter to a window using the private function 'CGSAddWindowFilter'.

typedef void * CGSConnectionID;

extern OSStatus CGSNewConnection(const void **attr, CGSConnectionID *id);

- (void)enableBlurForWindow:(NSWindow *)window
{

CGSConnectionID _myConnection;
uint32_t __compositingFilter;

int __compositingType = 1; // Apply filter to contents underneath the window, then draw window normally on top

/* Make a new connection to CoreGraphics, alternatively you could use the main connection*/

CGSNewConnection(NULL , &_myConnection);

/* The following creates a new CoreImage filter, then sets its options with a dictionary of values*/

CGSNewCIFilterByName (_myConnection, (CFStringRef)@"CIGaussianBlur", &__compositingFilter);
NSDictionary *optionsDict = [NSDictionary dictionaryWithObject:[NSNumber numberWithFloat:3.0] forKey:@"inputRadius"];
CGSSetCIFilterValuesFromDictionary(_myConnection, __compositingFilter, (CFDictionaryRef)optionsDict);

/* Now just switch on the filter for the window */

CGSAddWindowFilter(_myConnection, [window windowNumber], __compositingFilter, __compositingType );
}

Answer 2

The filters are not being used by the root layer: From the docs:

    /* An array of filters that are applied to the background of the layer.
 * The root layer ignores this property. Animatable. */

@property(copy) NSArray *backgroundFilters;

Answer 3

Your code has some error, here is the code that just works:

typedef void * CGSConnection;
extern OSStatus CGSNewConnection(const void **attributes, CGSConnection * id);

-(void)enableBlurForWindow:(NSWindow *)window {

    CGSConnection thisConnection;
    NSUInteger compositingFilter;
    NSInteger compositingType = 1 << 0;

    // Make a new connection to Core Graphics
    CGSNewConnection(NULL, &thisConnection);

    // Create a Core Image filter and set it up
    CGSNewCIFilterByName(thisConnection, (CFStringRef)@"CIGaussianBlur", &compositingFilter);
    NSDictionary *options = [NSDictionary dictionaryWithObject:[NSNumber numberWithFloat:2] forKey:@"inputRadius"];
    CGSSetCIFilterValuesFromDictionary(thisConnection, compositingFilter, (__bridge CFDictionaryRef)options);

    // Apply the filter to the window
    CGSAddWindowFilter(thisConnection, [window windowNumber], compositingFilter, compositingType);
}

Then, use it:

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
    [_window setOpaque:NO];

    [_window setBackgroundColor: [NSColor colorWithCalibratedHue:0.568 saturation:0.388 brightness:0.941 alpha:0.6]];

    [self enableBlurForWindow:_window];
}