Smoother Image Scaling in NSTableView Cells

By default, NSImageCell's scaling strategy can produce some unpleasantly sharp edges. I looked at a bunch of different solutions to this using the existing API, but finally settled on a simple subclass.

You can download it here, but here's the gist of it:

...
// make resizing look pretty

NSRect rect = NSMakeRect ( 0, 0, size.width, size.height );
NSImage * temp = [[NSImage alloc] initWithSize:rect.size];
[temp lockFocus];
[[NSGraphicsContext currentContext]
     setImageInterpolation: NSImageInterpolationHigh];
[temp unlockFocus];

// resize image

NSPoint point = NSMakePoint( startX, startY );
[myImage setSize: size];
[myImage setScalesWhenResized: YES];

// draw image in cell

[myImage compositeToPoint:point
                operation:NSCompositeSourceOver];
[temp release];
...

The results are pretty significant. Here's a before and after:



Here's a closeup:



I recommend not selecting this as a custom subclass directly in Interface Builder, but instead do this in the controller:

- (void) awakeFromNib
{
  NSTableColumn *thumbColumn;
  thumbColumn = [myTable tableColumnWithIdentifier:@"thumbnail"];
  THIImageCell * myImageCell = [[THIImageCell alloc] init];
  [iconColumn setDataCell: myImageCell];
  [myImageCell setImageAlignment:NSImageAlignCenter];
}

This should allow you to continue using NSImageCell's binding options through IB. Maybe it would work anyway, but I didn't try it.

I make no claims about this being the most efficient method available. If someone has suggestions for refinements, let me know.

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