Custom qrcode renderer to allow smooth resizing

src/qrcodelabel.cpp

@@ -0,0 +1,56 @@
+#include "qrcodelabel.h"
+
+QRCodeLabel::QRCodeLabel(QWidget *parent) :
+    QLabel(parent)
+{
+    this->setMinimumSize(1,1);
+    setScaledContents(false);
+}
+
+QSize QRCodeLabel::sizeHint() const
+{
+    int w = this->width();
+    return QSize(w, w);   // 1:1 
+}
+
+void QRCodeLabel::resizeEvent(QResizeEvent * e)
+{
+    if(!address.isEmpty())
+        QLabel::setPixmap(scaledPixmap());
+}
+
+QPixmap QRCodeLabel::scaledPixmap() const {
+    QPixmap pm(size());
+    pm.fill(Qt::white);
+    QPainter painter(&pm);
+    
+    qrcodegen::QrCode qr = qrcodegen::QrCode::encodeText(address.toUtf8().constData(), qrcodegen::QrCode::Ecc::LOW);
+    const int    s      = qr.getSize()>0?qr.getSize():1;
+    const double w      = pm.width();
+    const double h      = pm.height();
+    const double aspect = w/h;
+    const double size   = ((aspect>1.0)?h:w);
+    const double scale  = size/(s+2);
+    const double offset = (w - size) > 0 ? (w - size) / 2 : 0;
+    
+    // NOTE: For performance reasons my implementation only draws the foreground parts    
+    painter.setPen(Qt::NoPen);
+    painter.setBrush(QColor(Qt::black));
+    for(int y=0; y<s; y++) {
+        for(int x=0; x<s; x++) {
+            const int color=qr.getModule(x, y);  // 0 for white, 1 for black
+            if(0!=color) {
+                const double rx1=(x+1)*scale+ offset, ry1=(y+1)*scale;
+                QRectF r(rx1, ry1, scale, scale);
+                painter.drawRects(&r,1);
+            }
+        }
+    }
+    
+    return pm;
+}
+
+void QRCodeLabel::setAddress(QString addr) {
+    address = addr;
+    QLabel::setPixmap(scaledPixmap());
+}