Fixed an issue where the magnifier did not account for hiDPI on retin…

…a screens (#2187)

src/widgets/panel/colorgrabwidget.cpp

@@ -200,11 +200,26 @@ void ColorGrabWidget::updateWidget()
     float zoom = m_extraZoomActive ? ZOOM2 : ZOOM1;
     // Set window size and move its center to the mouse cursor
     QRect rect(0, 0, width, width);
+
+    auto realCursorPos = cursorPos();
+    auto adjustedCursorPos = realCursorPos;
+
+#if defined(Q_OS_MACOS)
+    QScreen* currentScreen = QGuiAppCurrentScreen().currentScreen();
+    if (currentScreen) {
+        adjustedCursorPos =
+          QPoint((realCursorPos.x() - currentScreen->geometry().x()) *
+                   currentScreen->devicePixelRatio(),
+                 (realCursorPos.y() - currentScreen->geometry().y()) *
+                   currentScreen->devicePixelRatio());
+    }
+#endif
+
     rect.moveCenter(cursorPos());
     setGeometry(rect);
     // Store a pixmap containing the zoomed-in section around the cursor
     QRect sourceRect(0, 0, width / zoom, width / zoom);
-    sourceRect.moveCenter(rect.center());
+    sourceRect.moveCenter(adjustedCursorPos);
     m_previewImage = m_pixmap->copy(sourceRect).toImage();
     // Repaint
     update();