NSImage is always being scaled and looks bad

Question

I want to create an NSImage of an NSScrollView object, so I can use the flat graphic for animation purposes.

When I render my scrollview object into a graphic and add it back to my window, it works but looks really bad like it's been scaled to 99% or something. I want the image to not be scaled and 100% pixel accurate. (Note: the image isn't scaled, it's the same size, it just looks like it's been poorly rescaled - the text looks rough and poor compared to the view onscreen in the scrollview)

My code: (scrollView is my NSScrollView object)

NSData *pdf = [scrollView dataWithPDFInsideRect:[scrollView bounds]];
NSImage *image = [[NSImage alloc] initWithData:pdf];

NSImageView *imageView = [[NSImageView alloc] initWithFrame:[scrollView bounds]];
[imageView setImage: image];
[mainGUIPanel addSubview: imageView];

I've tried a heap of things, messed with pixel sizes, bounds, used IB to create the destination NSView and put the image inside that but just cannot get the image to not look bad. Any ideas?

Edit: I tried writing the pdf data to a pdf file and viewed it, and it looked ok. So the bitmap image is being captured ok, it's just on the display that it looks like it's being scaled somewhat.

Edit2: Also tried getting the bitmap like this:

NSBitmapImageRep *bitmap = [scrollView bitmapImageRepForCachingDisplayInRect:[scrollView bounds]];
[scrollView cacheDisplayInRect:[scrollView bounds] toBitmapImageRep:bitmap];

NSImage * image = [[NSImage alloc] initWithSize:[bitmap size]];
[image addRepresentation: bitmap];

Same results - the bitmap looks exactly the same, bad and scaled when displayed.

This leads me to believe that capturing the bitmap data either way works fine, it's creating the view and rendering the image that is doing the scaling. How can I make sure that the view and image are shown at the correct size and scaling?

Edit3: Ok, I started a new blank project and set this up, and it works perfectly - the new imageview is identical to the grabbed bitmap. So I suspect my issue is stemming from some rendering/compositing issue when drawing the bitmap to the view. Investigating further...

It turns out the issue stems from the scrollView that I am rendering from. This has a transparent background (Draw Background is off in IB) and the text is the scrollView looks good. If I turn "Draw Background ON", with a transparent background color, the text is rendered badly, exactly as it is when I capture the image programatically.

So, in my app, even though Draw Background is off, the scrollView image is captured as though Draw Background is on. So I need to understand why the text is rendered badly when Draw Background is on and set to transparent, and hopefully this will lead me towards a solution.

Also tried creating an NSClipview with background drawing turned off and putting the bitmap view into that, but it sill renders the same. I can't find a way to render the transparent image to the screen without horrible artifacting.

Answer 1

Ok, I've found a solution. Instead of getting a grab of the transparent background scrollview object itself, I'm instead getting a grab of the parent view (essentially the window background), and restricting the bounds to the size of the scrollview object.

This captures both the background, and the contents of the scrollview, and displays correctly without any issues of transparency.