Take into account the space between above or below a QQuickWidget

Applications such as KDE Plasma's System Settings or the simpler Qt's
Quick Widgets Example are cases where there's space around the
QQuickWidget. For System Settings there is a toolbar below the widget,
and in the Qt example it's an MDI window. GammaRay failed at capturing
both of these, but this is easy to fix.

If we detect that we're inside a bigger window, take the height
difference into account. This completely fixes the capture of the
aforementioned examples, and doesn't seem to regress in other cases.

I only changed and tested on the >=6.8 ifdef branch, since I assume this
was broken when porting for the single surface changes.

Author: redstrate

plugins/quickinspector/quickscreengrabber.cpp

@@ -627,9 +627,14 @@ void OpenGLScreenGrabber::windowAfterRendering()
             QPoint offset;
             rc->renderWindow(&offset);
 
+            // If we are rendering into a window, we need to take into account the space between us and the bottom of the window (if any)
+            const auto renderWindow = rc->renderWindowFor(m_window);
+            if (renderWindow != nullptr) {
+                yOff = renderWindow->height() - m_renderInfo.windowSize.height() - offset.y();
+            }
             xOff = offset.x();
 #if QT_VERSION >= QT_VERSION_CHECK(6, 8, 0)
-            yOff = 0;
+            yOff = static_cast<int>(std::floor(yOff * m_renderInfo.dpr));
             xOff = static_cast<int>(std::floor(xOff * m_renderInfo.dpr));
 #else
             const auto viewportHeight = viewport[3];