OpenEuphoria

I don't know anything about SDL, but in order to debug this, you need to find out where the failure is occurring. I'd start by looking to answer a few questions:

• Does the blit code actually get called?
• Are the parameters correct?
• Does the image get loaded properly?
• Is everything initialized correctly inside of SDL

Also, you could simplify setting up the rectangle in memory:

procedure CalcRect(atom rect, integer sx, integer sy, integer tx, integer ty) 
    poke2( rect,  { sx, sy, tx, ty } ) 
end procedure