A Lua snippet that implements a stack of nested camera contexts. This makes it easier to apply translations when drawing composite graphics.

You can push new camera contexts with push_camera(x,y). This acts like a call to the standard camera function, but after this, all calls to camera are relative to x and y. You can return to the previous camera context by calling pop_camera().

You can push as many camera contexts onto the stack as memory allows.

An example of mixing push_camera and camera calls: Calling push_camera(-20,-30) sets the absolute camera coordinates to (-20,-30), like the standard camera function, and creates a new context. A subsequent call to camera(-1,2) sets the absolute camera coordinates to (-21,-28). Calling pop_camera() restores the absolute camera coordinates to the default of (0,0).

An example of pushing nested camera contexts: Calling to push_camera(-20,-30) sets the absolute camera coordinates to (-20,-30), like the standard camera function, and creates a new context. A subsequent call to push_camera(-1,2) sets the absolute camera coordinates to (-21,-28) and creates a new context. Calling pop_camera() restores the absolute camera coordinates to (-20,-30). Finally, calling pop_camera() restores the absolute camera coordinates to the default of (0,0).

do
 local cstack = {}
 local abscam = camera

 function push_camera(dx,dy)
  local cx,cy = peek2(0x5f28,2)
  add(cstack, {cx,cy})
  abscam(cx+dx,cy+dy)
 end

 function pop_camera()
  abscam(unpack(deli(cstack)))
 end

 function camera(dx,dy)
  local cx,cy =
    unpack(cstack[#cstack]or{})
  abscam(
    (cx or 0) + (dx or 0),
    (cy or 0) + (dy or 0))
 end
end

Ooops... I just fixed a bug in it.