Const iterators

[Adrian Page]

Boudewijn Rempt wrote:
> Is it maybe an idea to add const iterators for the paint devices some time 
> soon? I'm everlastingly either const_casting or removings consts because I 
> cannot read out a device const'ly...

Yes, we should have const iterators, or at least a way to access the 
data in a read-only manner.

I have been looking at the iterators lately and have thought about 
making some changes like this. We could make rawData() return a const 
Q_UINT8 *, and maybe have a function to copy into the data:

const Q_UINT8 *rawData()
void setRawData(const Q_UINT8 *src, Q_INT32 numPixels = 1)

An advantage of having a function to do the job of the memcpy is that we 
could track the exact extent of the data without having to do the pixel 
search that you do in exactExtent. Then everything that would benefit 
from an exact extent could just use it without having to think about it.

The same idea would apply to the KisPixel access. Instead of a KisPixel 
pointing to the raw data, allowing you to modify it directly, KisPixel 
would hold its own data and you would do an it.setPixel(pixel) to write it.

Another idea is to make iterators easier to use by being able to set and 
get QColors directly (until we replace QColor with KisColor). Either 
that or allow KisPixels to be settable to a QColor and return a QColor - 
no matter what colour space is in use.

It would be nice to be able to do things like

KisHLineIteratorPixel pixelIt = createHLineIteratorPixel(...);

QColor color = pixelIt.color();
... do something interesting with the color...
it.setColor(color);

The main thing is to hide the colour strategy and its 
nativeColor/toQColor etc, and just let you concentrate on the algorithm 
you're implementing. It would be good to hide the raw data access, 
memcpys, etc, particularly for people who are new to the code and, say, 
  want to write a simple plugin.

Currently accessing the data through KisPixel is a start but it still 
requires the use of colour strategies, which would be better hidden, 
although there for advanced use.

Adrian