Equivalent of GDIPlus::PathGradientBrush

Perdrix

In Microsoft GDIPlus I might have this code:

  Graphics graphics(hdc);// structure  Graphics  object 
  Pen m_pen(Color::Blue,2);
  SolidBrush m_Brush(Color::Green);
  
  Point points[] = {
     Point(30, 30), Point(180, 30), Point(180, 150), Point(30, 150) };

  PathGradientBrush pathBrush(points,4);// Use points to create brushes 

  pathBrush.SetCenterColor(Color::Red);// Set center color 

  Color colors[] = {
     Color::Green ,Color::Black,Color::Yellow,Color::Blue};
  int count = 4;
  pathBrush.SetSurroundColors(colors, &count);// Set the border color 

  graphics.FillRectangle(&pathBrush, 30, 30, 150, 120);

which would result in this:

How do I do that using Qt? I looked at QConicalGradient, but I couldn't see how I might use it to get that result :(

Note that in my case I'm dealing with triangles not squares.

Thanks
David

Chris Kawa

I don't think there's a built in gradient type in Qt that can do that in one pass. The best would be to create your own gradient type I think, but if you're ok with a multi-pass approach you could blend multiple linear gradients like this:

QRect r(0,0,200,200);
QPainter p(some_paint_device);

p.fillRect(r, Qt::red);

QLinearGradient g(r.topLeft(), r.center());
g.setColorAt(0,Qt::green);
g.setColorAt(1,Qt::transparent);
p.fillRect(r, g);

g.setStart(r.topRight());
g.setColorAt(0,Qt::black);
p.fillRect(r, g);

g.setStart(r.bottomRight());
g.setColorAt(0,Qt::yellow);
p.fillRect(r, g);

g.setStart(r.bottomLeft());
g.setColorAt(0,Qt::blue);
p.fillRect(r, g);

Obviously not a great solution if you have a lot of triangles to fill like that.