Drawing an image in a NSView

Question

I have a simple Obj C program that, at the moment, lets you load an image, draws it up, and theoretically should let you zoom and rotate. I'm using NSAffineTranslations.

I want the image to be locked to the upper left (As opposed to the PS/PDF standard of lower left), so I'm using isFlipped, and calling [afTrans scaleXBy:1.0 yBy:-1.0];

The problem is that for some reason, after the first time my drawRect is called, the transformation doesn't happen.

When I load an image, it comes up, and looks correct. If I change the size of the window (Which calls drawRect), the image draws, but is upside-down and reversed. This means that the transformation didn't take effect. I don't see any differences in any of the data the 2nd time through.

here is a stripped down version of the code:

- (void)drawRect:(NSRect)rect 
{
    // Drawing code here.

//    NSLog(@"window type: %d", [[self window] backingType]);
   NSAffineTransform *afTrans = [[NSAffineTransform alloc] init];
   NSGraphicsContext *context = [NSGraphicsContext currentContext];
   NSSize sz;
   NSRect windowFrame = [[self window] frame];
   NSRect cv =[[[self window] contentView] frame];
   float deltaX, deltaY;
   NSSize superSize = [[self superview] frame].size;
   float height, width, sHeight, sWidth;

   NSRect imageRect;

   sz = [ image size];
   imageRect.size = sz;
   imageRect.origin = NSZeroPoint;

   height = sz.height  ;
   width = sz.width  ;

//    sHeight and sWidth are the hieght and with of the super-view. ie,
//    the size of the whole window view including the space for the
//    scroll bars, etc, but not including the panel or the borders,
   sHeight = superSize.height;
   sWidth = superSize.width;

   [context saveGraphicsState];

   deltaX = 0;
   deltaY = 0;

   deltaY += height; // account for flipping

   [afTrans translateXBy:deltaX yBy:deltaY];

   [afTrans scaleXBy:1.0 yBy:-1.0];

   [afTrans concat];

   NSRect drawingRect = imageRect;
   NSRect frame = imageRect;
   [self setFrame:frame];

   [image drawInRect:drawingRect
         fromRect:imageRect
         operation:NSCompositeSourceOver
         fraction:1];

   [afTrans release];
   [context restoreGraphicsState];
}

ETA: here's some more code that MIGHT be relevant.

-(void )setImage:( NSImage * )newImage
{
    [newImage retain];
    [image release];

    rotation = 0;

    zoom = 1.0;

    image = newImage;
    NSSize imageSize = [newImage size];
    NSRect tFrame = [self frame];
    tFrame = [[self window] frame];

    tFrame.size.width = MAX(tFrame.size.width, imageSize.width);
    tFrame.size.height = MAX(tFrame.size.height, imageSize.height);
    [self setFrame:tFrame];

    [self setNeedsDisplay:YES];
}

Answer 1

I'm not sure exactly what you're trying to achieve, but if you want to just draw an image in a NSView and keep it in the upper left, you can do something a bit simpler, in your NSView subclass:

- (BOOL)isFlipped
{
    return YES;
}

- (void)setImage:(NSImage *)newImage
{
    [newImage retain];
    [image release];
    image = newImage;

    [image setFlipped:YES];
    [self setNeedsDisplay:YES];
}

- (void)drawRect:(NSRect)rect
{
    [image drawAtPoint:NSZeroPoint fromRect:NSZeroRect operation:NSCompositeSourceOver fraction:1];

    // Or stretch image to fill view
    //[image drawInRect:[self bounds] fromRect:NSZeroRect operation:NSCompositeSourceOver fraction:1];
}

I was also able to get similar results with your code by getting rid of the [self setFrame:...]; calls in drawRect and setImage methods.

Answer 2

Assuming you're not stripping out code that changes stuff, watch out if you're drawing the image elsewhere. Toolbar items, tables and so on may well change the -flipped property of the image, causing it to draw incorrectly.

Try this around your image drawing line:

BOOL wasFlipped = [image isFlipped];
[image setFlipped:[self isFlipped]];
[image drawInRect:drawingRect
             fromRect:imageRect
            operation:NSCompositeSourceOver
             fraction:1];
[image setFlipped:wasFlipped];

See if that helps. If it does, look elsewhere in your code for something changing the image's flipped property and not putting it back.