Also The icon is being manually drawn but it can be switch to using the image instead by change the #if 0 to #if 0 in icon_t.h in function icon_paint_icon
This demo also clips and only draws what it visible on screen so making the window lager will draw more and impact the performance more. The default size does not show much difference on my system but when I maximize the window it then shows for me.
there is also a render_everything flag in the frm_main.h which if set to true will even render off screen if needed to see the effect. same with the java version