Design ideas about iterators

[Patrick Julien]

I think you need to careful here.  Not only is this complicate, a template is 
not required to achieve this.

You can achieve the same effect by passing the originating paint device 
instead of the raster operation.

For example, if you place compositeIn has a member of KisPainter, you can 
define 'f' has a member of the color strategy.  You get the exact same code 
sharing between the color strategies by placing it like this.  However, look 
at what it does to the user of the code, it makes the selection of 'f' 
transparent.

On March 2, 2004 07:49 pm, Cyrille Berger wrote:
> > GEGL seems to try to achieve color models and bit depths by generating C
> > code using a special language that combines algorithms and specifications
> > -- if I understood the documentation and code correctly. That looks a lot
> > like templates, I guess, but I'm not sure.
>
> 1) It looks like oriented object in C too.
> Templates are powerfull, but they can destroy us, a bit like the Dark
> Side... If we want to use them, we will have to check what are the common
> functions.
>
> I see that  composite.h could be transform using templates like that :
> template < int depth, QUANTUM (*f)(QUANTUM, QUANTUM, double, double),
> QUANTUM (*g)(double, double)>
> void compositeIn(Q_INT32 stride,
> 		 QUANTUM *dst,
> 		 Q_INT32 dststride,
> 		 QUANTUM *src,
> 		 Q_INT32 srcstride,
> 		 Q_INT32 rows,
> 		 Q_INT32 cols,
> 		 QUANTUM opacity = OPACITY_OPAQUE)
> {
> 	if (opacity == OPACITY_TRANSPARENT)
> 		return;
> 	QUANTUM *d;
> 	QUANTUM *s;
> 	Q_INT32 i;
> 	double sAlpha, dAlpha;
> 	double alpha;
> 	while (rows-- > 0) {
> 		d = dst;
> 		s = src;
> 		for (i = cols; i > 0; i--, d += stride, s += stride) {
> 			if (s[PIXEL_ALPHA] == OPACITY_TRANSPARENT)
> 			{
> 				memcpy(d, s, stride * sizeof(QUANTUM));
> 				continue;
> 			}
> 			if (d[PIXEL_ALPHA] == OPACITY_TRANSPARENT)
> 				continue;
> 			sAlpha = QUANTUM_MAX - s[PIXEL_ALPHA];
> 			dAlpha = QUANTUM_MAX - d[PIXEL_ALPHA];
> 			for( int i = 0; i < depth; i++)
> 			{
> 				d[ i ]=f( s[ i ], sAlpha, d[ i ], dAlpha );
> 			}
> 			d[PIXEL_ALPHA]=g(salpha, dalpha);
> 		}
> 		dst += dststride;
> 		src += srcstride;
> 	}
> }
>
> And so we can define an only tileBlt for all colorspace. And we may get
> ride of enum CompositeOp.
> But I can't see how we can get ride of some constant, such as const
> REDCHANNEL, GREENCHANNEL, BLUECHANNEL, GRAYCHANNEL, INDEXEDCHANNEL,
> ALPHACHANNEL...
>
> And we still need "enum enumImgType", even with template. Even if it is
> just to say the user : "it's a CMYB image".
>
>
> 2) I just sea an interesting idea for iterators in GEGL's documentation, we
> should do an iterator that return an other iterator which will contain a
> line. I don't think I am clear, we may have an iterator called iteratorLine
> which return an iteratorPixel.
> We may use them this way :
> for( iteratorLine iL = image->getIterator() ; iL != iL.end(); iL++)
> // go through lines
> {
> 	for( iteratorPixel iP = *iL; iP != iP.end(); iP++)
> 	{
> 		*iP = 0; // Clear the pixel
> 	}
> }