Creating windows offscreen for fun and profit.

offscreen.m

- (IBAction)getImageFromWeb:(id)sender {
    // grab the width and height of the document in our mobileView.
    CGSize contentSize = CGSizeMake(
        [[mobileView stringByEvaluatingJavaScriptFromString:@"document.body.scrollWidth;"] floatValue],
        [[mobileView stringByEvaluatingJavaScriptFromString:@"document.body.scrollHeight;"] floatValue]
    );

    // create a new window, offscreen.
    NSWindow *hiddenWindow = [[NSWindow alloc] initWithContentRect: NSMakeRect( -1000,-1000, contentSize.width, contentSize.height  ) 
    styleMask: NSTitledWindowMask | NSClosableWindowMask backing:NSBackingStoreNonretained defer:NO];

    // grab the dimensions of the viewport of the mobileView, and create a frame for our WebView that matches the dimensions of the document that is loaded.
    NSView *viewport = [[[mobileView mainFrame] frameView] documentView]; // width/height of html page
    NSRect viewportBounds = [viewport bounds];
    NSRect frame = NSMakeRect(0.0, 0.0, contentSize.width, contentSize.height);

    // create a new web view to attach to our hidden window.
    WebView *hiddenWebView = [[WebView alloc] initWithFrame:frame frameName:@"Hidden.Frame" groupName:nil];

    // grab the value of textField as a string
    NSString *hURL = [textField stringValue];

    // set hiddenWebView as the content of hiddenWindow
    [hiddenWindow setContentView:hiddenWebView];

    // call loadRequest on hiddenWebView, converting our hURL string to a URLRequest object.
    [[hiddenWebView mainFrame] loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:hURL]]];

    // we lock our focus on the WebView. This becomes important later when we want to capture this WebView.
    [hiddenWebView lockFocus];

    // as long as the URL is loading, stick right here.
    while ([hiddenWebView isLoading]) {
        [hiddenWebView setNeedsDisplay:NO];
        [NSApp nextEventMatchingMask:NSAnyEventMask untilDate:[NSDate dateWithTimeIntervalSinceNow:1.0] inMode:NSDefaultRunLoopMode dequeue:YES];
    }
    
    // once the loading condition is satisfied we can move on.
    [hiddenWebView setNeedsDisplay:YES];

    // the first step is to create a bitmap (referenced internally as bitmap) that corresponds to the dimensions of our WebView.
    // you can see now why we locked focus on the WebView, as we are creating this bitmap by telling it to look at the FocusedView.
    bitmap = [[NSBitmapImageRep alloc] initWithFocusedViewRect:viewportBounds];
    
    // now that we have grabbed our image, lets release the focus on the WebView.
    [h iddenWebView unlockFocus];

    // convert our bitmap to an image for previewing.
    NSImage *dispImage = [[NSImage alloc] initWithData:[bitmap TIFFRepresentation]];
    
    // Display the image by assigning it to an NSImageView.
    [imagePreview setImage:dispImage];
}