I'm trying to draw a 3-pixel large point with QPainter
. But the following code instead draws a horizontal line with width of 3 pixels.
#include <QPainter>
#include <QImage>
int main()
{
const int w=1000, h=1000;
QImage img(w, h, QImage::Format_RGBX8888);
{
QPainter p(&img);
p.fillRect(0,0,w,h,Qt::black);
p.scale(w,h);
p.setPen(QPen(Qt::red, 3./w, Qt::SolidLine, Qt::RoundCap));
p.drawPoint(QPointF(0.1,0.1));
}
img.save("test.png");
}
Here's the top left corner of the resulting image:
I am expecting to get a point which is red circle, or at least a square — but instead I get this line segment. If I comment out p.scale(w,h)
and draw the point with width 3
(instead of 3./w
) at position (100,100)
, then I get a small mostly symmetric 3-pixel in height and width point.
What's going on? Why do I get a line segment instead of point as expected? And how to fix it, without resorting to drawing an ellipse or to avoiding QPainter::scale
?
I'm using Qt 5.10.0 on Linux x86 with g++ 5.5.0. The same happens on Qt 5.5.1.