FillRectVsNSRectFill

last edited April 13, 2004 16:13:04 (80.199.113.18)
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CocoaDrawing

I'm trying to fill an NSView subclass (actually ScreenSaverView subclass) with [NSColor clearColor], but [NSBezierPath fillRect:] doesn't work the way I'd expect. First I run: 

[[self window] setOpaque:0];
[[NSColor clearColor] set];
[[self window] setBackgroundColor:[NSColor clearColor]]; // not sure if this is necessary
Then I try to fill the NSView with clear with: 
[NSBezierPath fillRect:[self frame]];
but it doesn't work! But the following line does work: 
NSRectFill([self frame]);
What's going on here?

You have to refresh the NSView.

Does that mean NSRectFill? draws directly onscreen? Will it be copied to the window's offscreen buffer? EnglaBenny 
NSRectFill(...);
does not overlay onto the background, it simply blasts the pixels in the specified rectangle to whatever NSColor has been set. However, you can use 
NSRectFillUsingOperation(...);
to (somewhat) mimick the NSBezierPath method.

Ok I ran a side-by-side test on -[NSBezierPath fillRect:] vs. NSRectFill?(). These are two NSViews? whose drawRect: methods call the rectangle-filling routine, both with pure red at 50% alpha.

image

Now I think I get it...-[NSBezierPath fillRect:] overlays a rectangle of the current color over the background.

Another difference seems to be that NSRectFill? uses pixel coordinates, whereas fillRect does not. I.e. if I fill a box e.g. @(10, 10) size: 100x100 it will have a fuzzy edge with fillRect (because the coordinate system is offset by half a pixel) which it does not when using NSRectFill?.