Add wxTextCtrl::PositionToCoords() functions for wxMSW and wxGTK.

The new method allows to find the coordinates in pixels of the given character
in a text control.

Closes #13221.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68450 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/textctrl.cpp

@@ -1218,6 +1218,37 @@ int wxTextCtrl::GetLineLength(long lineNo) const
     }
 }
 
+wxPoint wxTextCtrl::DoPositionToCoords(long pos) const
+{
+    if ( !IsMultiLine() )
+    {
+        // Single line text entry (GtkTextEntry) doesn't have support for
+        // getting the coordinates for the given offset. Perhaps we could
+        // find them ourselves by using GetTextExtent() but for now just leave
+        // it unimplemented, this function is more useful for multiline
+        // controls anyhow.
+        return wxDefaultPosition;
+    }
+
+    // Window coordinates for the given position is calculated by getting
+    // the buffer coordinates and converting them to window coordinates.
+    GtkTextView *textview = GTK_TEXT_VIEW(m_text);
+
+    GtkTextIter iter;
+    gtk_text_buffer_get_iter_at_offset(m_buffer, &iter, pos);
+
+    GdkRectangle bufferCoords;
+    gtk_text_view_get_iter_location(textview, &iter, &bufferCoords);
+
+    gint winCoordX = 0,
+         winCoordY = 0;
+    gtk_text_view_buffer_to_window_coords(textview, GTK_TEXT_WINDOW_WIDGET,
+                                          bufferCoords.x, bufferCoords.y,
+                                          &winCoordX, &winCoordY);
+
+    return wxPoint(winCoordX, winCoordY);
+}
+
 int wxTextCtrl::GetNumberOfLines() const
 {
     if ( IsMultiLine() )