I'm creating a window in my dual monitor setup configured with Nvidia's Twinview.
The problem is no combination of position and size parameters can make a window become fullscreen at the correct resolution on one the secondary monitor, it always picks up the size of the first monitor. 

My metamode is:

./nv-control-dpy --print-current-metamode

Using NV-CONTROL extension 1.27 on :0
Connected Display Devices:
  CRT-1 (0x00000002): CVT Crystal View
  DFP-0 (0x00010000): DELL 2408WFP

current metamode: "id=50, switchable=yes, source=xconfig :: CRT-1: nvidia-auto-select @1024x768 +0+0, DFP-0: nvidia-auto-select @1920x1200 +1024+0"


If I create a window with:

SDL_CreateWindow("test",1024, 0,1920,1200, SDL_WINDOW_FULLSCREEN)

everything looks nice, a full screen window on my primary monitor of the correct resolution.

But if I do:

SDL_CreateWindow("test",0, 0,1024,768, SDL_WINDOW_FULLSCREEN)

...hoping to get a full screen 1024x768 on the left side monitor (which is the secondary in my setup), I get a fullscreen window that's 1920x1200 (it starts correctly at 0x0 though, but it "overflows" the secondary monitor because it's of a lower resolution).

I've also tried with SDL_WINDOWPOS_UNDEFINED | display_number, but that doesn't work in this case, I think because boths monitors appear as a single display to SDL.

The internal value _this->num_displays used in SDL_GetWindowDisplay is always 1 (that may explain the problem, at least partially)

In SDL 1.2 apps, I can set the SDL_VIDEO_FULLSCREEN_HEAD to 0 or 1 and I'll get the app on the appropriate monitor and at the correct resolution (I tested this with the Humble Bundle V apps).