fltk_custom_drawing.puml

@startwbs
+ **custom drawing with FLTK**
 + **analysis:**
  + **""fl_graphics_driver"":**\n• widgets use ""Fl/fl_draw.H"" to draw,\n• ""fl_graphics_driver"" is declared in ""FL/Fl_Graphics_Driver.H"",\n• ""Fl/fl_draw.H"" delegates most drawing functions to ""fl_graphics_driver"",\n• can be set directly or through ""FL/Fl_Device.H"".
  + **relation of surfaces to graphics drivers:**\n• a surface references a graphics driver,\n• a way of setting/restoring ""fl_graphics_driver"".
  + **conclusions:**\n• implement a custom ""Fl_Graphics_Driver"" for ""cairo"",\n• implement a custom ""Fl_Surface_Device"" for ""cairo"",\n• use  ""Cairo_Surface_Device::set_current()"" to set the graphics driver,\n• draw the background and then the children.
@endwbs