Horizontal and vertical QLineargradient

Question

I'm trying to generate a clickable HVS colorspace widget using `QGraphicsView`. The background of the whole `QGraphicsView` shall look like the image below (without jpeg-artefacts). Clicking at position (x,y) shall give the color under the cursor. I don't want to use the image directly, instead I thought about using `QLinearGradient` in both directions (horizontal & vertical) using Qt stylesheets. Simply using horizontal colorstops is straight forward, but I can't figure out how to add the additional vertical (white-color-black) gradient. What I got so far (inside constructor of inherited class from `QGraphicsView`) is: ``` QColor hsvColor[6]; hsvColor[0].setHsv(0, 255, 255); hsvColor[1].setHsv(60, 255, 255); hsvColor[2].setHsv(120, 255, 255); hsvColor[3].setHsv(180, 255, 255); hsvColor[4].setHsv(240, 255, 255); hsvColor[5].setHsv(300, 255, 255); QString styleH = QString("background-color: qlineargradient(spread:pad, x1:0, y1:0, x2:1, y2:0,") + QString("stop:0.000 rgba(%1, %2, %3, 255…

Accepted Answer

The trick here is to have 2 gradients in your `QGraphicsView`, one set as the background for the colors (left to right), one set as the foreground (top to bottom).

```
// a colored background based on hue
QLinearGradient colorGradient = QLinearGradient(0, 0, width(), 0);
colorGradient.setSpread(QGradient::RepeatSpread);
colorGradient.setColorAt(0, QColor(255,255,255));
colorGradient.setColorAt(1, currentHue);

QLinearGradient blackGradient = QLinearGradient(0, 0, 0, height());
blackGradient.setSpread(QGradient::RepeatSpread);
blackGradient.setColorAt(0, QColor(0,0,0,0));
blackGradient.setColorAt(1, QColor(0,0,0,255));

QBrush colorGradiantBrush = QBrush(colorGradient);
QBrush blackGradiantBrush = QBrush(blackGradient);
scene.setBackgroundBrush(colorGradiantBrush);
scene.setForegroundBrush(blackGradiantBrush);
```

The code above gives you a palette with one color like this:

For the foreground, I used a transparent to black — you will need a white to transparent, to black. And for the background, I used a white to a specific color — you can use your spectrum that you already have.

Horizontal and vertical QLineargradient

Solution

Problem