@Tiny-Leaf
Try the following code. The length of three segments should be same.

drawLine(ctx, 50, 50, 150, 50); drawLine(ctx, 150, 50, 50, 50); drawLine(ctx, 150, 100, 50, 100); function drawLine(ctx, x1, y1, x2, y2) { ctx.beginPath() ctx.moveTo(x1, y1) ctx.lineTo(x2, y2) ctx.stroke() }

BTW: you may somehow avoid to draw a line twice if possible. It is not efficient.

Finally coming back to this ... and found the issue :-)

DBGWebPage *NewPage = new DBGWebPage(webGUI);

The new Page was not a child of the correct object.
I checked pointers as suggested.
The connect of the JS bridge showed no issues.
However, the first call from JS (signal javaScriptWindowObjectCleared() calling my populateJavaScriptWindowObject())
crashed on

QWebFrame * webGUIframe = qobject_cast<QWebFrame *>(sender()); QWebView * webGUI = (QWebView*)(webGUIframe->parent())->parent();

obviously because it was pointing to 'nothing' instead of a QWebView.
Thank you guys for all the hints.