Different transparencies in Cocoa? - objective-c

Question

I have overloaded NSWindow and have created a custom window of my own (Borderless and transparency of 0.3 alphaValue). I am going to be drawing images in this window. Is there any way I can get the images that will be drawn in the window opaque? I want the window to remain transparent but want the images to be opaque. How would I do this?
Mac OS X Snow Leopard
Xcode 3.2.6

Answer 1

#ughoavgfhw is on the right track, but it's actually much easier. You just need to set opaque to NO and set backgroundColor to semi-transparent.
#implementation MYWindow
- (void)setup
{
[self setStyleMask:NSBorderlessWindowMask];
[self setOpaque:NO];
[self setBackgroundColor:[NSColor colorWithCalibratedWhite:1.0 alpha:0.3]];
}
// We override init and awakeFromNib so this works with or without a nib file
- (id)initWithContentRect:(NSRect)contentRect styleMask:(NSUInteger)aStyle backing:(NSBackingStoreType)bufferingType defer:(BOOL)flag
{
self = [super initWithContentRect:contentRect styleMask:aStyle backing:bufferingType defer:flag];
if (self)
{
[self setup];
}
return self;
}
- (void)awakeFromNib
{
[super awakeFromNib];
[self setup];
}
#end

Answer 2

There's a potential problem with this approach.
Requesting "[self setStyleMask:NSBorderlessWindowMask];" (with any of the possible StyleMask values) will cause the loss of keystroke events to that window on subsequent presentations of the window as a sheet. I reported a bug to Apple today on this point.

Answer 3

Leave the alphaValue property to 1, and set the opaque property to NO. Then, replace the default contentView with one which fills itself with a color whose alpha component is 0.3 in its drawRect: method. When you change the alphaValue property, it changes how everything drawn in the window is displayed. When you make it non-opaque, it simply doesn't draw a black background beneath the content view, so if the content view is transparent, the window will be too, but anything drawn on top of that will not be affected.
Here's an example which uses a white background with a 0.3 alpha component. Note that I overrode the setContentView: method. This is so that I can copy any views from the passed view into the transparent content view, and is especially necessary if you load the window from a nib, since the nib loading will change the content view when it is loaded. (You could change the content view's class in IB instead.)
#interface MyWindow_ContentView : NSView
#end
#implementation MyWindow
- (id)initWithContentRect:(NSRect)contentRect styleMask:(NSUInteger)aStyle backing:(NSBackingStoreType)bufferingType defer:(BOOL)flag {
if(self = [super initWithContentRect:contentRect styleMask:aStyle backing:bufferingType defer:flag]) {
[super setOpaque:NO];
[super setContentView:[[[MyWindow_ContentView alloc] init] autorelease]];
}
return self;
}
- (void)setOpaque:(BOOL)ignored {}
- (void)setContentView:(NSView *)newView {
NSArray *views = [[self.contentView subviews] copy];
[views makeObjectsPerformSelector:#selector(removeFromSuperview)];
views = [[newView subviews] copy];
[views makeObjectsPerformSelector:#selector(removeFromSuperview)];
for(NSView *view in views) [self.contentView addSubview:view];
[views release];
}
#end
#implementation MyWindow_ContentView
- (void)drawRect:(NSRect)rect {
[[NSColor colorWithCalibratedWhite:1 alpha:0.3] set];
NSRectFill(rect);
}
#end