Complete source code of spEngine.dll is available at GitHub: https://github.com/spetric/SigmaPi-Engine.
SigmaPi-Engine or shortly spEngine is main drawing, image editing and image processing engine used by Pixopedia XE. spEngine is in charge for handling all drawing, filters, IPP filters, IPP convolution, IPP histogram manipulation and many more. All brushes, stroke effects and various brush arithmetics reside inside spEngine library (spEngine.dll).
You can use it from Embarcadero C++ without any modifications and if you want to use it from Delphi program, someone needs to convert two header files to Delphi pas files.
If you want to port the engine to MSVC or some other C++ compiler/platform, you need to change few things in code (rough description on GitHub page).
Have fun 🙂