IDA SDK C++ tricks and tips

[chants]

We see in graph.hpp the following events:

  grcode_user_title,          ///< render node title of a user-defined graph.
                              ///< \param g               (::mutable_graph_t *)
                              ///< \param node            (int)
                              ///< \param title_rect      (::rect_t *)
                              ///< \param title_bg_color  (int)
                              ///< \param dc              (HDC)
                              ///< \retval 0  did not render, ida will fill it with title_bg_color
                              ///< \retval 1  rendered node title

  grcode_user_draw,           ///< render node of a user-defined graph.
                              ///< NB: draw only on the specified DC and nowhere else!
                              ///< \param g          (::mutable_graph_t *)
                              ///< \param node       (int)
                              ///< \param node_rect  (::rect_t *)
                              ///< \param dc         (HDC)
                              ///< \retval 0  not rendered
                              ///< \retval 1  rendered

But HDC is certainly NOT what you thought it might be - a windows handle to a device context as IDA is totally portable. So after taking a stack trace, decompiling IDA64.exe and tracing the argument, its in fact a QT::QPainter object pointer. Basically the QT equivalent of a device context.

https://doc.qt.io/qt-5/qpainter.html

This is another totally undocumented, even if logical feature present. Unfortunately you must compile with QT headers, should link with the exact QT libs that IDA uses so it will reuse the QT DLL included with IDA, in this case for QTPainter - Qt5Gui.dll version 5.6.3.0