I have created a very simple test project to try and get this to work.

In the main.nib I created a borderless General/NSImageView, which I then connected to an outlet in an General/AppController I created. The implementation for my General/AppController looks like this

@implementation General/AppController

• (void) awakeFromNib { [theImageView setImage:General/[NSImage imageNamed:@”ipcLogoWhite”]]; General/NSImage *theImage = [theImageView image]; General/NSRect theImageFrame = [theImageView bounds]; General/NSSize imgSize = [theImage size]; General/NSRect srcRect = General/NSMakeRect( 0.0, 0.0, imgSize.width, imgSize.height ); [theImage drawInRect:theImageFrame fromRect:srcRect operation:General/NSCompositeSourceIn fraction:1.0]; } @end

What i was hoping was that the image I set to appear inside the General/NSImageView would become transparent and I would see the image looking through to the background of the window. If you look at any apple installer you will see what I am talking about. A screenshot of what I am aiming for is included below

http://www.kirkconsulting.co.uk/public/General/TransparentBackground.jpg.

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You might try subclassing General/NSImageView to return NO for -isOpaque. Don’t know if this will work, but it’s a shot.

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I tried subclassing and overriding the return value on this method but to no avail. It seems that the drawInRect:fromRect:operation:fraction: method doesn’t have any effect at all. To prove this I tried changing the fromRect to something arbitarilly smaller than it should be and it doesn’t redraw the image any smaller. What gives?

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OK - So I nailed it in the end. I had already opened up the NIB from Apple’s Installer to see how it was done but I found the contents confusing. There was an object somewhere behind everything set to a custom class which was doing the work, but I couldn’t see it. I assumed wrongly that this was not a custom view. Actually, I discovered that it is possible to have a custom view that does not show in Interface Builder, if you resize it to fill the whole window and then double click it!

Anyway, now I new that the object was a subclass of General/NSImageView and I set to work trying to make my own that would do the same job. I came up with this:

/* General/JKBackgroundImage */

#import <Cocoa/Cocoa.h>

@interface General/JKBackgroundImage : General/NSImageView { General/NSImage *image; float opacity; }

• (void) setImage:(General/NSImage *) newImage;
• (void) setOpacity:(float)x; @end

#import “General/JKBackgroundImage.h”

@implementation General/JKBackgroundImage

• (void) setImage:(General/NSImage *) newImage { [newImage retain]; [image release]; image = newImage; }

• (void) setOpacity: (float) x { opacity = x; [self setNeedsDisplay:YES]; }

• (void) drawRect: (General/NSRect)rect { [self setImageScaling:General/NSScaleToFit]; if (image) { General/NSRect theFrame = [self bounds]; General/NSSize imgSize = [image size]; General/NSRect srcRect = General/NSMakeRect( 0.0, 0.0, imgSize.width, imgSize.height ); [image drawInRect:theFrame fromRect:srcRect operation:General/NSCompositeSourceOver fraction:opacity]; } } @end

then in my General/AppController I just set the opacity and the image and voila! I have acheived exactly the effect shown in the picture I posted.

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It’s kind of wasteful to have this inherit from General/NSImageView. You get a bunch of extra clutter from General/NSImageView and General/NSControl that doesn’t affect the drawing of your view at all (and thus actually makes your view’s interface deceptive). You’d be better off with just an General/NSView subclass.