save the current items on qwidget as image - c++

Question

I'm trying draw some rhombuses with random colors in a QWidget. And i want to save the current QWidget as image. I use such code to do this:
QPixmap pixmap(this->size());
this->render(&pixmap);
pixmap.save("test.png");
The problem is that the render() seems to call paintEvent again, and the paintEvent will draw the rhombuses with new random colors, so that i always get a different Image saved compared to the image displayed. Can someone tell me how to save the current QWidget? Thanks in advance.
Code for drawing rhombuses:
void Dialog::paintEvent(QPaintEvent *e) {
QPainter painter(this);
QRect background(0,0,this->geometry().width(),this->geometry().height());
painter.setBrush( QBrush( Qt::white ) );
painter.setPen( Qt::NoPen );
//QBrush bbrush(Qt::black,Qt::SolidPattern);
painter.drawRect(background);
int width = this->geometry().width();
int height = this->geometry().height();
//draw rectangles
int rec_size=64;
int rows=0;
int cols=0;
rows=floor((double)height/(double)rec_size);
cols=floor((double)width/(double)rec_size);
QPointF points[4]; // QRect rec(0,0,rec_size,rec_size);
for (int i=0;i<floor(rows);i++){
for (int j=0;j<floor(cols);j++){
painter.setBrush( QBrush( colors[rand() % color_size] ) );
//QPainter painter(this);
points[0] = QPointF(rec_size*(j),rec_size*(i+0.5));
points[1] = QPointF(rec_size*(j+0.5),rec_size*(i));
points[2] = QPointF(rec_size*(j+1),rec_size*(i+0.5));
points[3] = QPointF(rec_size*(j+0.5),rec_size*(i+1));
painter.drawPolygon(points, 4);
}
}
painter.end();
}

Answer 1

You can have a class member variable of boolean type to check in the paintEvent whether a random color should be used. Also a variable to save the index of the last color used is necessary:
bool isRandom;
int lastColor;
The paintEvent should be like :
void Dialog::paintEvent(QPaintEvent *e) {
...
if(isRandom)
{
lastColor = rand() % color_size;
painter.setBrush( QBrush( colors[lastColor] ) );
}
else
painter.setBrush( QBrush( colors[lastColor] ) );
...
}
The variable has true when drawing the widget regularly. When you want to save it's image, assign the variable to false, save the image and assign it to true again :
isRandom = false;
QPixmap pixmap(this->size());
this->render(&pixmap);
pixmap.save("test.png");
isRandom = true;