Programmatically edit image in Cocoa? - cocoa

Question

I want to set a custom mouse cursor for my app and would like to programmatically change the default cursor's color to a custom color by replacing the white border with the custom color. The problem is that I don't even know where to start to programmatically edit images in Cocoa, so any help is appreciated!

Answer 1

You can get the default cursor with -[NSCursor arrowCursor]. Once you have a cursor, you can get its image with -[NSCursor image]. You shouldn't modify another object's image, so you should copy that image. Then you should edit the image, and create a new cursor with -[NSCursor initWithImage:hotSpot:]. Your code should look something like this:
- (NSImage *)customArrowCursorImage {
NSImage *image = [[[NSCursor arrowCursor] image] copy];
[image lockFocus];
/// Do custom drawing
[image unlockFocus];
}
- (NSCursor *)customArrowCursor {
NSImage *image = [self customArrowCursorImage];
NSPoint hotSpot = [[NSCursor arrowCursor] hotSpot];
return [[[NSCursor alloc] initWithImage:image hotSpot:hotSpot] autorelease];
}
You should be able to replace the white color of the image with a custom color by using a core image filter. But if you just want to get started, you can use NSReadPixel() and NSRectFill to color one pixel at a time. Drawing one pixel a a time like that with with NSReadPixel and NSRectFill will be exceptionally slow, so you should only do that to get a feel for how all of this works.

Answer 2

My final code. This takes the standard IBeam cursor (that one when you hover over a textview) and stores the colored cursor in the coloredIBeamCursor pointer.
- (void)setPointerColor:(NSColor *)newColor {
// create the new cursor image
[[NSGraphicsContext currentContext] CIContext];
// create the layer with the same color as the text
CIFilter *backgroundGenerator=[CIFilter filterWithName:#"CIConstantColorGenerator"];
CIColor *color=[[[CIColor alloc] initWithColor:newColor] autorelease];
[backgroundGenerator setValue:color forKey:#"inputColor"];
CIImage *backgroundImage=[backgroundGenerator valueForKey:#"outputImage"];
// create the cursor image
CIImage *cursor=[CIImage imageWithData:[[[NSCursor IBeamCursor] image] TIFFRepresentation]];
CIFilter *filter=[CIFilter filterWithName:#"CIColorInvert"];
[filter setValue:cursor forKey:#"inputImage"];
CIImage *outputImage=[filter valueForKey:#"outputImage"];
// apply a multiply filter
filter=[CIFilter filterWithName:#"CIMultiplyCompositing"];
[filter setValue:backgroundImage forKey:#"inputImage"];
[filter setValue:outputImage forKey:#"inputBackgroundImage"];
outputImage=[filter valueForKey:#"outputImage"];
// get the NSImage from the CIImage
NSCIImageRep *rep=[NSCIImageRep imageRepWithCIImage:outputImage];
NSImage *newImage=[[[NSImage alloc] initWithSize:[outputImage extent].size] autorelease];
[newImage addRepresentation:rep];
// remove the old cursor (if any)
if (coloredIBeamCursor!=nil) {
[self removeCursorRect:[self visibleRect] cursor:coloredIBeamCursor];
[coloredIBeamCursor release];
}
// set the new cursor
NSCursor *coloredIBeamCursor=[[NSCursor alloc] initWithImage:newImage hotSpot:[[NSCursor IBeamCursor] hotSpot]];
[self resetCursorRects];
}