_l_e_f_t is the x coordinate of the viewport left side.
_r_i_g_h_t is the x coordinate of the viewport right side.
_b_o_t_t_o_m is the y coordinate of the viewport bottom.
_t_o_p is the y coordinate of the viewport top.
DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
vvvviiiieeeewwwwppppoooorrrrtttt specifies, in pixels, the area of the window that displays an
image. The viewport locations are specified relative to the lower-left
corner of the window. Specifying the viewport is the first step in
mapping world coordinates to screen coordinates. The portion of world
space that wwwwiiiinnnnddddoooowwww, oooorrrrtttthhhhoooo, or ppppeeeerrrrssssppppeeeeccccttttiiiivvvveeee describes is mapped into the
viewport. _l_e_f_t, _r_i_g_h_t, _b_o_t_t_o_m, and _t_o_p coordinates define a rectangular
area on the screen.
When the system is not in feedback mode the rectangular area is
restricted as follows. The valid range for _l_e_f_t, and _r_i_g_h_t is
-ggggeeeettttggggddddeeeesssscccc((((GGGGDDDD____XXXXPPPPMMMMAAAAXXXX)))) to 2*ggggeeeettttggggddddeeeesssscccc((((GGGGDDDD____XXXXPPPPMMMMAAAAXXXX)))). The valid range for _b_o_t_t_o_m,
and _t_o_p is -ggggeeeettttggggddddeeeesssscccc((((GGGGDDDD____YYYYPPPPMMMMAAAAXXXX)))) to 2*ggggeeeettttggggddddeeeesssscccc((((GGGGDDDD____YYYYPPPPMMMMAAAAXXXX)))). The maximum
width and height is 2K.
vvvviiiieeeewwwwppppoooorrrrtttt also loads the screenmask.
SSSSEEEEEEEE AAAALLLLSSSSOOOO
scrmask, getviewport, popviewport, pushviewport
NNNNOOOOTTTTEEEE
On the Personal Iris, if _l_e_f_t is greater than _r_i_g_h_t or _b_o_t_t_o_m is greater
than _t_o_p, the screen displays a reflected image.