QLinearGradient inconsistent behavior with QPainter::drawLine

**Santosh Reddy** · 26th April 2013, 14:03

After looking at this post, I did a small program to test the QLinearGradient, and it appears that that QLinearGradient does not affect the perfect horizontal and perfect vertical lines, that drawn using QPainter::drawLine(). Before I convince myself that this is a bug I wanted to check with the forum that did I miss anything?

Here is an example, note the perfect horizontal and perfect vertical line are not affected by gradient. I have tested this on
1. Qt 4.8.1, MinGw 4.6.2, Win 7 32 bit
2. Qt 5.0.1, MinGw 4.7.0, Win 7 32 bit

Here is the Qt 5.0.1 example
QLinearGradient.jpg

Qt Code:

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#include <QtGui>
#include <QtWidgets>
#include <QApplication>
 
class Widget : public QWidget
{
public:
    Widget(QWidget *parent = 0) : QWidget(parent) {}
 
protected:
    void paintEvent(QPaintEvent *)
    {
        QLinearGradient v = QLinearGradient(QPointF(0,0), QPointF(0,1));
        v.setCoordinateMode(QGradient::ObjectBoundingMode);
 
        QLinearGradient h = QLinearGradient(QPointF(0,0), QPointF(1,0));
        h.setCoordinateMode(QGradient::ObjectBoundingMode);
 
        QBrush vBrush(v);
        QBrush hBrush(h);
 
        QPainter painter(this);
 
        QPen p = painter.pen();
        p.setWidth(25);
 
        p.setBrush(vBrush);
        painter.setPen(p);
        painter.drawLine(QPointF(100,100),QPointF( 99,200));
        painter.drawLine(QPointF(200,200),QPointF(200,100));
        painter.drawLine(QPointF(300,100),QPointF(301,200));
 
        p.setBrush(hBrush);
        painter.setPen(p);
        painter.drawLine(QPointF(400,100),QPointF(500, 99));
        painter.drawLine(QPointF(400,200),QPointF(500,200));
        painter.drawLine(QPointF(400,300),QPointF(500,301));
    }
};
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
 
    Widget * widget = new Widget;
    widget->setWindowTitle("QLinearGradient");
    widget->showMaximized();
 
    return a.exec();
}

#include <QtGui>
#include <QtWidgets>
#include <QApplication>

class Widget : public QWidget
{
public:
    Widget(QWidget *parent = 0) : QWidget(parent) {}

protected:
    void paintEvent(QPaintEvent *)
    {
        QLinearGradient v = QLinearGradient(QPointF(0,0), QPointF(0,1));
        v.setCoordinateMode(QGradient::ObjectBoundingMode);

        QLinearGradient h = QLinearGradient(QPointF(0,0), QPointF(1,0));
        h.setCoordinateMode(QGradient::ObjectBoundingMode);

        QBrush vBrush(v);
        QBrush hBrush(h);

        QPainter painter(this);

        QPen p = painter.pen();
        p.setWidth(25);

        p.setBrush(vBrush);
        painter.setPen(p);
        painter.drawLine(QPointF(100,100),QPointF( 99,200));
        painter.drawLine(QPointF(200,200),QPointF(200,100));
        painter.drawLine(QPointF(300,100),QPointF(301,200));

        p.setBrush(hBrush);
        painter.setPen(p);
        painter.drawLine(QPointF(400,100),QPointF(500, 99));
        painter.drawLine(QPointF(400,200),QPointF(500,200));
        painter.drawLine(QPointF(400,300),QPointF(500,301));
    }
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    Widget * widget = new Widget;
    widget->setWindowTitle("QLinearGradient");
    widget->showMaximized();

    return a.exec();
}

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