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List:       kde-kimageshop
Subject:    Re: optimizing the scaling code
From:       Casper Boemann <cbr () boemann ! dk>
Date:       2005-06-28 8:34:00
Message-ID: 200506281034.00655.cbr () boemann ! dk
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On Tuesday 28 June 2005 09:41, Michael Thaler wrote:
> Hello,
>
> I think the main speed problem in my current scaling code is that I read
> single pixels using
>
> QUANTUM *tmp = new QUANTUM[ pixelSize * sizeof(QUANTUM) ];
> m_dev -> readBytes(tmp, x, y, 1, 1);
>
> I am currently rewriting the code to read whole lines and I wonder what is
> the best way to do this. Casper's transform visitor does this:
>
> KisHLineIteratorPixel srcIt = src->createHLineIterator(left, y, w, true);
> int i = 0;
> while(!srcIt.isDone())
> {
>         Q_UINT8 *data;
>         data = srcIt.rawData();
>         memcpy(&tmpLine[i*pixelSize], data, pixelSize);
>         ++srcIt;
>         i++;
> }
>
> which creates a temporary array with the pixel data of a line.
>
> Another method would be to just use
>
> QUANTUM *tmp = new QUANTUM[ width * pixelSize * sizeof(QUANTUM) ];
> m_dev -> readBytes(tmp, 0, y, width, 1);
>
> What is faster? Or is there any other method to read a line as fast as
> possible?
about the same.

the advantage of using an iterator could be if you need to do some per pixel 
work while reading

btw I now see that I can optimize my code here, by using the number of 
consequtive  pixels to copy larger blocks. This is actually a reason to use 
readBytes as that function is likely to be update with such fixes faster than 
your own code.
-- 
best regards / venlig hilsen
Casper Boemann
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