[Qt-interest] QImage fade

[Mihail Naydenov]

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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