I'm using an AMD FirePro W5100 on Windows 10 x64 1703. Driver version 21.19.384.0.
The maximum hardware surface size as returned by IDirect3D9_GetDeviceCaps() is 16384×16384 pixels (MaxTextureWidth & MaxTextureHeight).
However, the maximum DirectDraw surface size appears to be only 4096×4096 pixels; IDirectDraw7_CreateSurface() fails if either dimension is larger than 4096.
So I have a couple of questions: