Re: Graphics Rounding (was Re: Pixel-aligned autoresizing)

[Fred Kiefer]

On 09.07.2011 21:04, Eric Wasylishen wrote:
> Hi Philippe,
>
> The jumping is caused by our use of rint() in NSButtonCell - in fact, I think we should 
> avoid rint() entirely for graphics, because it uses a "round halfway cases to the 
> nearest even integer" algorithm; so 1.5 rounds to 2, but 2.5 also rounds to 2.
>
> The annoying thing is that none of the C standard library functions implement a 
> good rounding algorithm for graphics. c99's round() rounds halfway cases away 
> from zero. This is probably OK in practice but not ideal, since it means the 
> location of the coordinate system origin affects the rounding. I think the best 
> algorithm for graphics is round-towards-infinity, so just floor(x+0.5). I 
> wonder if we should just introduce this as a function for internal use, like 
> GSRoundTowardsInfinity().
>
> Eric

Hi Eric,

could you please explain why you think that one of these rounding 
methods is better suited for graphics than the others? For me they are 
all equally problematic :-(
If we ever change to another function we will have to make sure it is 
available equally on all supported systems. That way why I wanted to 
stick with rint() for all cases as we already try to support that 
everywhere.

Fred

PS: I also don't see how pure horizontal resizing may affect the 
vertical position of a subview. Is this the case that mentioned earlier, 
but couldn't come up with a real test case for?