Add a white background to an NSImage that is larger than the original image

Question

I am currently adding a solid white background to an NSImage so that in the case that the image has a transparent background it becomes opaque.

What I would like to be able to do is increase the size of the white background so that it extends out all around the original image (thus giving it a white border).

This is what I currently have, but I can't work out how to create the white image larger that the original.

NSImage* importedImage = [bitmapImage image];

NSSize imageSize = [importedImage size];
NSImage* background = [[NSImage alloc] initWithSize:imageSize];

[background lockFocus];
[[NSColor whiteColor] setFill];

[NSBezierPath fillRect:NSMakeRect(0, 0, imageSize.width, imageSize.height)];
[background unlockFocus];

theImage = [[NSImage alloc] initWithSize:imageSize];
[theImage lockFocus];
CGRect newImageRect = CGRectZero;
newImageRect.size = [theImage size];
[background drawInRect:newImageRect];
[importedImage drawInRect:newImageRect];
[theImage unlockFocus];

Answer 1

I finally solved this. First I get the size of the original image and create the white background to this size plus twice the width of the border that I want.

Then, I create a new image and draw in the white background, then the original image making sure that its origin = the border width.

-(NSImage*) addBorderToImage:(NSImage *)theImage
{

//get the border slider value...
float borderWidth = [borderSlider floatValue];

//get the size of the original image and incease it to include the border size...
NSBitmapImageRep* bitmap = [[theImage representations] objectAtIndex:0];
NSSize imageSize = NSMakeSize(bitmap.pixelsWide+(borderWidth*2),bitmap.pixelsHigh+(borderWidth*2));

//create a new image with this size...
NSImage* borderedImage = [[NSImage alloc] initWithSize:imageSize];

[borderedImage lockFocus];

//fill the new image with white...
[[NSColor whiteColor] setFill];
[NSBezierPath fillRect:NSMakeRect(0, 0, imageSize.width, imageSize.height)];

//rect of new image size...
CGRect newImageRect = CGRectZero;
newImageRect.size = [borderedImage size];

//rect of old image size positioned inside the border...
CGRect oldImageRect = CGRectZero;
oldImageRect.size = [theImage size];
oldImageRect.origin.x = borderWidth;
oldImageRect.origin.y = borderWidth;

//draw in the white filled image...
[borderedImage drawInRect:newImageRect];
//draw in the original image...
[theImage drawInRect:oldImageRect];
[borderedImage unlockFocus];

return borderedImage;

}