[Webkit-unassigned] [Bug 50527] [Qt] Background image rendering is slow

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=50527





--- Comment #9 from Noam Rosenthal <noam.rosenthal at nokia.com>  2010-12-06 07:54:08 PST ---
(In reply to comment #6)
> (From update of attachment 75618 [details])
> View in context: https://bugs.webkit.org/attachment.cgi?id=75618&action=review
> 
> > WebCore/platform/graphics/qt/ImageQt.cpp:125
> > +    // FIXME: Might be worth investigating to cache the transformed result, though this has memory implications.
> > +    QPixmap tilePixmap;
> > +    if (tileRect.x() || tileRect.y() || tileRect.width() != framePixmap->width() || tileRect.height() != framePixmap->height() || !patternTransform.isIdentityOrTranslation()) {
> > +        // We can't use the pixmap as is, because we're using only part of it or it needs to be scaled. Because we know the pixmap is going to be
> > +        // drawn more than once, we copy/scale it only once to avoid repeating the operation for each tile.
> > +        QRect targetTileRect = patternTransform.mapRect(tileRect);
> > +        tilePixmap = QPixmap(targetTileRect.size());
> > +        QPainter painter(&tilePixmap);
> > +        painter.setCompositionMode(QPainter::CompositionMode_Source);
> > +        painter.setTransform(patternTransform);
> > +        painter.translate(-targetTileRect.topLeft());
> > +        painter.drawPixmap(tileRect, *framePixmap);
> > +    } else
> 
> I don't think that would work with rotation so you don't implement the interface given by the API of ImageBuffer.
> I would prefer if you change the function signature to take two arguments scaleX and scaleY so it is explicit that any other type transform is not supported.
> 
> Otherwise, future change to support arbitrary transform from CSS would break Qt.
Yes, I agree. Or maybe, we can do this for scale/translate only and go through QPixmap::transformed as a fallback.

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