[Qt-interest] Memory mapping QImage

[Kustaa Nyholm]

Hi,

currently I'm copying the contents of a QImage to a memory mapped file
with something like this:


   char* mmap = (char*) mmap(0, .....
   for (int i=0; i<mImage.height(); ++i) {
       uchar* p=;  
       memcpy(
           mmap +i*mImage.bytesPerLine(),
           mImage.scanLine(i) ,
           mImage.bytesPerLine());
       }

this works and is reasonably fast for my purpose.

However it seems slightly sub-optimal because of the
copying. Ideally I could just pass the memory mapped
file pointer to QImage to use as the pixel store
and no copying would be involved.

But I can't find a public method for that.

Is there some way to accomplish this?

I'm using the QImage as a paint device in a lighthouse

QPaintDevice *JEmbedWindowSurface::paintDevice()
{
    return &mImage;
}

so it does not 'have to' be a QImage, but that
was the best I could find.

I could probably eliminate the for loop and
get away with a slightly faster:


       memcpy(
           mmap,
           mImage.scanLine(0) ,
           mImage.bytesPerLine()*mImage.height());

but that would violate the scanLine() contract, what?

br Kusti