But I am using my own math for a bit tighter fitting shadow depth maps than what at least gamestudio does and also some basic technique to get rid of any flickering when moving the camera. The result are quite high resolution and flicker free shadows. To speed up the rendering I also experimented with layered rendering which with the help of geometry shaders would allow to draw the shadow maps with triangle culling in just one rendering pass. But it turned out that the overhead of geometry shaders is extremely bad, slowing things down a lot.
For the surface acne issues I am using a so called "slope scale depth bias" which is an extremely simple to use OpenGL and also DirectX feature which is around for a long time already.
Shadow filtering is a bigger problem and currently not really solved. What is used in the screenshots is just 2x2 percentage closer filtering (actually a bit more thanks to some hardware feature), but anything bigger will get much too slow.