[Qt-interest] QImage fade

[Joshua Grauman]

Mihail,

Thanks for the suggestion. I've tried multiple times to do this directly 
with QPainter and as far as I can tell it isn't possible directly (at 
least not without extra deep copies of the entire QImage). If someone has 
a direct way to do this with QPainter, I'd love to see it! Thanks.

Josh

> The main speedup is not to do it yourself probably.
>
> I do not know I you have tested it, but this is trivial using the painter.
> Especially if this is for the screen and you can use Pixmaps.
>
> MihailNaydenov
>
>
>
> ----- Original Message ----
>> From: Joshua Grauman <jnfo-c at grauman.com>
>> To: qt-interest at qt.nokia.com
>> Sent: Sat, May 7, 2011 3:41:44 AM
>> Subject: [Qt-interest] QImage fade
>>
>> Hello all,
>>
>> I've written a little function to fade two QImages to a 3rd.  It works fine
>> and the results are expected. I cycle through fadeval values  to fade the
>> two images. I was wondering if anyone had any tricks I'm missing  to *speed
>> it up* though...
>>
>> FYI the function is dependant on all three  QImages being the same size,
>> and they all need to be  QImage::Format_ARGB32...
>>
>>
>> static int fadeMax=50;
>>
>> void  fadeImages(QImage *dest, QImage *src1, QImage *src2, unsigned char
>> fadeval)
>> {
>>    for(int y = 0; y < dest->height(); y++)
>>     {
>>      QRgb *destrow = (QRgb*)dest->scanLine(y);
>>       QRgb *src1row = (QRgb*)src1->scanLine(y);
>>      QRgb  *src2row = (QRgb*)src2->scanLine(y);
>>      for(int x = 0; x <  dest->width(); x++)
>>      {
>>        ((unsigned  char*)&destrow[x])[0] = (((unsigned
>> char*)&src1row[x])[0]*fadeval/fadeMax + ((unsigned
>> char*)&src2row[x])[0]*(fadeMax-fadeval)/fadeMax);
>>         ((unsigned char*)&destrow[x])[1] = (((unsigned
>> char*)&src1row[x])[1]*fadeval/fadeMax + ((unsigned
>> char*)&src2row[x])[1]*(fadeMax-fadeval)/fadeMax);
>>         ((unsigned char*)&destrow[x])[2] = (((unsigned
>> char*)&src1row[x])[2]*fadeval/fadeMax + ((unsigned
>> char*)&src2row[x])[2]*(fadeMax-fadeval)/fadeMax);
>>         ((unsigned char*)&destrow[x])[3] = 255;
>>      }
>>     }
>> }
>>
>>
>> Josh
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>