QPainter::DrawText antialiasing not work

jronald

Env

Linux KDE
Qt 6.3.0

Screenshot

Code

QPixmap pixmap(page_size);
painter.begin(&pixmap);
painter.setRenderHints(QPainter::Antialiasing | QPainter::TextAntialiasing);
font.setStyleStrategy(QFont::PreferAntialias);
font.setHintingPreference(QFont::PreferFullHinting);
painter.setFont(font);
painter.drawText(text_origin, qs_text);
painter.end();

More Info

A similar post: https://forum.qt.io/topic/111322/high-dpi-support-qpainter-drawtext
It doens't solve the problem for me.

Question

How to draw everything antialiasing in Qt6?

ralienpp

It could be related to the fact that you're drawing it on a QPixMap: https://bugreports.qt.io/browse/QTBUG-22334.

Do you use DPI scaling in your desktop environment? If yes, with what setting?

ChrisW67

Since you have taken a screenshot rather than inspected the actual QPixmap you are subject to whatever scaling happened putting the image on the screen. If that scaling up in size is not a nice ratio then you will see it. What is in the actual pixmap?

This code with Qt 6.2.3 on Linux:

#include <QGuiApplication>
#include <QFont>
#include <QPixmap>
#include <QPainter>

int main(int argc, char **argv) {
        QGuiApplication app(argc, argv);

        QFont font("Verdana");
        QPoint text_origin(50, 20);
        QString qs_text("890,321,832.65");

        QPixmap pixmap(800, 600);
        pixmap.fill();
        QPainter painter;
        painter.begin(&pixmap);
        painter.setPen(Qt::green);
        painter.setRenderHints(QPainter::Antialiasing | QPainter::TextAntialiasing);
        font.setStyleStrategy(QFont::PreferAntialias);
        font.setHintingPreference(QFont::PreferFullHinting);

        for (int size = 8; size < 40; size += 2) {
                font.setPointSize(size);
                painter.setFont(font);
                painter.drawText(text_origin, qs_text);

                QFontMetrics fm(font);
                painter.translate(0, fm.lineSpacing());
        }

        painter.end();

        pixmap.save("test.png");

        return 0;
}

produces this quite clean pixmap: