Comments on: Accelerating color gradients

By: kdepepo

kdepepo — Wed, 05 May 2010 14:08:33 +0000

@Alex, the code is in KDE svn It basically goes like this (not tested):

QImage image(2, 2); // 4-point gradient
image.setPixel(0, 0, QColor(Qt::black).rgb());
image.setPixel(0, 1, QColor(Qt::green).rgb());
image.setPixel(1, 0, QColor(Qt::red).rgb());
image.setPixel(1, 1, QColor(Qt::yellow).rgb());

QRect destRect(0, 0, 200, 200);
painter.setRenderHint(QPainter::SmoothPixmapTransforms, true);
painter.drawImage(destRect, image, QRectF(0.5, 0.5, 1, 1));

By: Johannes

Johannes — Wed, 05 May 2010 05:47:40 +0000

@kdepepo: Your right! Sorry I sometimes write before I think.

By: Alex

Alex — Wed, 05 May 2010 05:27:42 +0000

For those of us slowpokes d’you mind sharing a piece of code?

By: kdepepo

kdepepo — Tue, 04 May 2010 19:21:28 +0000

@Johannes, if you do a linear blend between red and green, you do not get a full yellow, but something darker:
http://www.herethere.net/~samson/php/color_gradient/?cbegin=FF0000&cend=00FF00&steps=4

By: Johannes

Johannes — Tue, 04 May 2010 16:29:30 +0000

Why is the image 7×2 and not 4×2 (red,green,blue,red)?

By: kdepepo

kdepepo — Tue, 04 May 2010 10:52:51 +0000

@Heller, the gradient changes depending on the value in the slider next to it, so you would have to store 256 images (actually 1536, because there are 6 “modes” the gradient can be in).

By: Heller

Heller — Tue, 04 May 2010 07:54:27 +0000

This may be obvious to you but why it is not possible to use a simple png to display this gradient ?

By: Alex

Alex — Mon, 03 May 2010 22:13:31 +0000

Clever!