[Bf-committers] [Bf-blender-cvs] SVN commit: /data/svn/bf-blender[11919] trunk/blender/source/blender/imbuf/intern/divers.c: Bugfix #7125

[Martin Poirier]

--- paprmh <paprmh at gmail.com> wrote:

> >
> > --- Ton Roosendaal <ton at blender.org> wrote:
> >
> > > Revision: 11919
> > >
> > >
> >
> >
>
http://projects.blender.org/plugins/scmsvn/viewcvs.php?view=rev&root=bf-blender&revision=11919
> > > Author:   ton
> > > Date:     2007-09-02 18:34:02 +0200 (Sun, 02 Sep
> > > 2007)
> > >
> > > Log Message:
> > > -----------
> > > Bugfix #7125
> > >
> > > The conversion from float to char (byte) was not
> > > correct. It should include
> > > the possibility for colors like 0.999999 to
> become
> > > 255 still. The correct
> > > multiplication factor I don't know though... and
> > > this should become a system
> > > wide definition!
> > >
> 
> 
> 
> From: Martin Poirier <theeth at yahoo.com>
> > You can probably use that too:
> >
> > #define FTOCHAR(val) val<=0.0f?0: (val>(1.0f -
> 0.5f /
> > 255.0f)?255: (char)(255.0f*val))
> >
> > Multiplying by 255.99 will give values 1 higher
> than
> > they should be for float values > 0.5. (I dealt
> with a
> > similar issue at work, that's more or less what we
> > used).
> >
> > Martin
> 
> 
> ...
> 
> That was assuming rounding, of course, in this case,
> > it's truncating on cast, so you can use:
> >
> > #define FTOCHAR(val) val<=0.0f?0: (val>(1.0f -
> 1.0f /
> > 255.0f)?255: (char)(255.0f*val))
> >
> > The 0.5 was to make it round in the correct
> direction.
> >
> > Martin
> 
> 
> Isn't the cast truncate bug a problem over the whole
> range of values? Not
> only is it important to round up anything 254.5
> (1.0f - 0.5f /255.0f) or
> higher to 255, but you need to address for instance,
> a value like
> 0.49fwhich would work out to
> 124.95 and get truncated to 124.
> I suggest using this:
> 
> #define FTOCHAR(val) val<=0.0f? 0 : (val>(1.0f -
> 0.5f /255.0f)? 255 :
> (char)((255.0f*val)+0.5f))
> 
> Adding .5 allows val to properly round up when the
> char cast truncates the
> float.  It also has the advantage of working over
> the entire range of values
> and not just for 255.  Here, checking for 254.5
> (1.0f - 0.5f /255.0f)
> instead of 1.0f is just more efficient as any value
> higher will round up to
> 255 anyway...
> 
> I found this tip a long time ago on the web when I
> needed a set of
> conversion functions for my seq plugins...and it has
> worked well there.

You're right, that would probably work better than a
straight cast.

Martin


       
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