Hello,

I create the application with the FLTK library. Almost everything works as it should, except one important thing, and  I couldn't find the right solution so far. Random artifacts appear in the window. They also appear randomly - sometimes everything is displayed correctly, but sometimes there are strange lines, some parts of the controls are not refreshed etc. I tried to use Fl::check() but it didn't help in every case. Please see the included examples (a strange black line over the window, a strange blue line over the button, and a broken frame around the button). How can I avoid these problems?