@thehans said in QOpenGLWidget::grabFrameBuffer() always ignores alpha channel?:

Unfortunately I'm on Ubuntu 18.04 which is still on 5.9.5.
Is there any chance of this fix being backported to earlier versions?

Qt 5.9 is now in "very strict" update mode, which means in only receives security fixes. It no longer receives bug fixes.

Your options are:

Download and use Qt 5.12 or newer from https://www.qt.io/download-open-source, OR Apply the patch to your copy of Qt 5.9 and build it from source.

I think the first option is easier.

I've figured this out. The problem wasn't in fact due to image files pixel alpha. That works just fine. It had to do with the QQuickView not being transparent. What I am doing is displaying a QQuickView as a borderless window to be used as a popup dialog and I want to see through to the background, where there are no objects in the qml file. (Think of a pop up dialog with rounded corners).

Here's what I'm doing:

QQuickView view; // don't display an icon in the task bar // no border on the window view.setFlags(Qt::SubWindow | Qt::FramelessWindowHint); // make the view transparent so that the edges of the window, // where there is no image, show through to the background QSurfaceFormat surfaceFormat; surfaceFormat.setAlphaBufferSize(8); view.setFormat(surfaceFormat); view.setClearBeforeRendering(true); view.setColor(QColor(Qt::transparent)); // load qml file and display view.setSource(file.qml); view.show();