Improve QRgb documentation

- Add examples of how to create QRgb values
- Link to qRgba()

Pick-to: 5.15 5.12
Change-Id: I2a86b1c8e00137ba868426b8157a3aa0d924d7a6
Reviewed-by: Venugopal Shivashankar <Venugopal.Shivashankar@qt.io>

src/gui/doc/snippets/code/src_gui_painting_qcolor.cpp

@@ -66,6 +66,14 @@ painter.setBrush(QColor(0, 0, 255, 127));
 painter.drawRect(0, 0, width(), height() / 2);
 //! [0]
 
+//! [QRgb]
+const QRgb rgb1 = 0x88112233;
+const QRgb rgb2 = QColor("red").rgb();
+const QRgb rgb3 = qRgb(qRed(rgb1), qGreen(rgb2), qBlue(rgb2));
+const QRgb rgb4 = qRgba(qRed(rgb1), qGreen(rgb2), qBlue(rgb2), qAlpha(rgb1));
+//! [QRgb]
+Q_UNUSED(rgb3);
+Q_UNUSED(rgb4);
 
 } // wrapper
 } // src_gui_painting_qcolor

src/gui/painting/qcolor.cpp

@@ -3203,7 +3203,11 @@ const uint qt_inv_premul_factor[256] = {
     channel is \c ff, i.e opaque. For more information, see the
     \l{QColor#Alpha-Blended Drawing}{Alpha-Blended Drawing} section.
 
-    \sa QColor::rgb(), QColor::rgba()
+    Here are some exammples of how QRgb values can be created:
+
+    \snippet code/src_gui_painting_qcolor.cpp QRgb
+
+    \sa qRgb(), qRgba(), QColor::rgb(), QColor::rgba()
 */
 
 /*!