Foreign declaration:   SDL_CreateRGBSurface > x i i i i i i i i

sdlprep =: 3 : 0
'width height'=. y
  sdl_init SDL_INIT_EVERYTHING
  appw=:sdl_createwindow 'test window';0;0;width;height;SDL_WINDOW_SHOWN+SDL_WINDOW_ALLOW_HIGHDPI
  appr=:sdl_createrenderer appw;_1;SDL_RENDERER_ACCELERATED+SDL_RENDERER_PRESENTVSYNC
  'ww wh'=:2}.sdl_getwindowsize appw;(,_1);(,_1)
  'rw rh'=:2}.sdl_getrendereroutputsize appr;(,_1);(,_1)
  NB. cxm=: rw % ww
  NB. cym=: rh % wh
  smoutput 'window:', (":appw), 'renderer:', (":appr)
  smoutput 'render width:',(":rw),' height:',(":rh)
  smoutput 'window width:',(":ww),' height:',(":wh)
  NB. This needs to be endian-aware at some point
  args=.0;rw;rh;32;16bff0000;16bff00;16bff;16bff000000
  smoutput args
  sfc=: sdl_creatergbsurface args
  NB. Practice structures. PACKING!!! Show printable format name
  pFormat=._3 ic memr (sfc+8),0,8 NB. sdl_surface->format
  format=._2 ic memr pFormat,0,4  NB. sdl_surface->format->format
  smoutput 'pixel format:',(psz sdl_getpixelformatname format)
  EMPTY
)

output when running...

window:140547920885040renderer:140547920929408
render width:1024 height:768
window width:1024 height:768
┌─┬────┬───┬──┬────────┬─────┬───┬──────────┐
│0│1024│768│32│16711680│65280│255│4278190080│
└─┴────┴───┴──┴────────┴─────┴───┴──────────┘
|domain error: sdl_creatergbsurface
|   sfc=:    sdl_creatergbsurface args
   cder''
6 1

The arg in question is the 1024, in a variable called rw, renderer width, but if I call by hand it works i.e. using numbers to set the surface dimensions:

   sdl_creatergbsurface 0;1024;768;32;16711680;65280;255;4278190080
140547918948464

Not sure why it won't take the value of the 'rh' variable?!?!!