Attempting to switch /dev/dri/cardX to /dev/dri/renderDY is futile
on its own now since many output-related drm operations fail and we
eventually crash.
Add a new headless mode that skips the real screen stuff and registers
a fairly dummy, headless screen, does not bother with the mouse cursor,
and disallows rendering to the screen via a QWindow (while keeping the
actual rendering still fully functional).
Such applications will not need any special privileges and will run even
if there is a DRM master (X11, Wayland compositor) active.
For example the configuration can look like this:
{
"device": "/dev/dri/renderD128",
"headless": "1024x768"
}
After this applications have two choices to perform offscreen
rendering:
1. Use an ordinary window (and its default framebuffer, meaning the
gbm_surface), e.g. a QOpenGLWindow subclass
MyOpenGLWindow w;
w.show(); // will not actually show on screen
w.grabFramebuffer().save("output.png");
Note that there is no vsync-based throttling. Also note that windows are
still sized to match the screen size, hence the need for specifying a size
in the headless property.
2. Or the typical offscreen approach with an extra FBO
QOffscreenSurface s;
s.setFormat(ctx.format());
s.create();
ctx.makeCurrent(&s0;
QOpenGLFramebufferObject fbo(1024, 768);
fbo.bind();
ctx.functions()->glClearColor(1, 0, 0, 1);
ctx.functions()->glClear(GL_COLOR_BUFFER_BIT);
fbo.toImage().save("output.png");
ctx.doneCurrent();
Task-number: QTBUG-62262
Change-Id: Ic1dbfa2b27b223bd5ef8ba36b665f0f61abf4f06
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Andy Nichols <andy.nichols@qt.io>
cf24d20385