[Interest] QImage + pixel lambdas

[Jason H]

channel ARGB32 6000000 pixels 87/88/93 msec (lambda, scanline)
channel ARGB32 6000000 pixels 148/146/153 msec QImage::pixel

> Sent: Friday, June 01, 2018 at 4:13 PM
> From: "Jason H" <jhihn at gmx.com>
> To: "Jason H" <jhihn at gmx.com>
> Cc: "interestqt-project.org" <interest at qt-project.org>
> Subject: Re: [Interest] QImage + pixel lambdas
>
> Incase anyone is wondering:
> accumulator ARGB32 6000000 pixels 24/25/26 msec (lamda, scanline)
> accumulator ARGB32 6000000 pixels 40/42/44 msec (lambda or no lambda, QImage::pixel)
> 
> 
> > Sent: Friday, June 01, 2018 at 9:38 AM
> > From: "Jason H" <jhihn at gmx.com>
> > To: "interestqt-project.org" <interest at qt-project.org>
> > Subject: [Interest] QImage + pixel lambdas
> >
> > So I'm doing some qimage analysis/manipulation. I think it would be really good if QImage came with a per-pixel function. (Examples below)
> > I'm tired of writing the x/y for loops. The really neat thing (not in the examples) is using QImage::scanLine(int y) for faster access, and automatically choosing the value of p in the lambda based on bit depth. 
> > 
> > Anyone else think this is a good idea?
> > 
> > //Really sorry about this SFINAE
> > template <typename T, typename std::enable_if<std::is_same<void, decltype(std::declval<T>()(1))>::value, int>::type = 0>
> > void eachPixel(const QImage &image, T pixelFunc, const QRect &bounds=QRect()) {
> > 	QRect imageRect(QRect(0,0, image.width(), image.height()));
> > 	QRect region = bounds.isNull() ? imageRect : bounds.intersected(imageRect);
> > 
> > 	for (int y=region.y(); y<=region.bottom(); y++) {
> > 		for (int x=region.x(); x<=region.right(); x++) {
> > 			pixelFunc(image.pixel(x,y));
> > 		}
> > 	}
> > }
> > 
> > //Really sorry about this SFINAE too. 
> > template <typename T, typename std::enable_if<std::is_same<uint, decltype(std::declval<T>()(1))>::value, int>::type = 0>
> > QImage eachPixel(const QImage &image, T pixelFunc, const QRect &bounds=QRect()) {
> > 	QRect imageRect(QRect(0,0, image.width(), image.height()));
> > 	QRect region = bounds.isNull() ? imageRect : bounds.intersected(imageRect);
> > 
> > 	QImage out(image.size(), image.format());
> > 	for (int y=region.y(); y<=region.bottom(); y++) {
> > 		for (int x=region.x(); x<=region.right(); x++) {
> > 			out.setPixel(x,y, pixelFunc(image.pixel(x,y)));
> > 		}
> > 	}
> > 	return out;
> > }
> > 
> > void test_pixelFunc() {
> > 	QImage image(300,200, QImage::Format_ARGB32);
> > 	image.fill(Qt::blue);
> > 
> > 	QImage out = eachPixel(image, [] (uint p)  {
> > 		return qRgb(qRed(p), qBlue(p), qGreen(p)); // swap green and blue channels 
> > 	}, QRect (5,5, 300, 200));                         // for a portion of the image
> > 	out.save("test_pixelfunc.png");
> > 
> > 
> > 	int accumulator=0;
> >         int min = 255;
> >         int max = 0
> > 	eachPixel(image, [&accumulator, &min, &max](uint p) {         // This one can be used for statistics,
> > 		accumulator +=p;                                      // if you're not making a new image
> >                 if (p < min) min = p;
> >                 if (p > max) max = p;
> > 	}, QRect (5,5, 300, 200));
> > 	qDebug() << "accumulator" << accumulator << "min" << min << "max" << max;
> > 
> > }
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>