' Scrolling background demo
' Allan Crossman 2001

leftkey$ = "4"
rightkey$ = "6"
upkey$ = "8"
downkey$ = "5"

fullwidth = 640
fullheight = 320

sw = fullwidth / 2
sh = fullheight / 2

cls

fullbackground = init screen (0, 0, fullwidth, fullheight)
set screen to fullbackground
cls
for n = 1 to 1000         ' Make stars on background.
   x = rnd * fullwidth
   y = rnd * fullheight
   brightness = rnd * 65535
   forecolor brightness, brightness, brightness
   plot x, y
next n

virtue = init screen (0, 0, sw, sh)
set screen to virtue
cls

set sprite render port to virtue
no sprite background
set sprite mask color to 0, 0, 0

forecolor 65535, 65535, 0
fcircle 10, 10, 9
ship = grab sprite (0, 0, 20, 20)

cls

shipx = fullwidth / 2
shipy = fullheight / 2

speedx = 0
speedy = 0

cleft = (screen width / 2) - (sw / 2)
ctop = (screen height / 2) - (sh / 2)
cright = (screen width / 2) + (sw / 2)
cbottom = (screen height / 2) + (sh / 2)
resize console cleft, ctop, cright, cbottom

controls$ = leftkey$ + ", " + rightkey$ + ", " + upkey$ + ", " + downkey$
set console title to "Move with " + controls$


MainLoop:

starttime = timer

keymap scan
if keymap key (leftkey$) then speedx = speedx - 0.5
if keymap key (rightkey$) then speedx = speedx + 0.5
if keymap key (upkey$) then speedy = speedy - 0.5
if keymap key (downkey$) then speedy = speedy + 0.5

' Speed limiter...

if abs(speedx) > 5 then speedx = sgn(speedx) * 5
if abs(speedy) > 5 then speedy = sgn(speedy) * 5

' Move the ship...

shipx = shipx + speedx
shipy = shipy + speedy

' Walls stop motion...

if shipx < 10 then
   shipx = 10
   speedx = 0
end if
if shipy < 10 then
   shipy = 10
   speedy = 0
end if
if shipx > (fullwidth - 10) then
   shipx = (fullwidth - 10)
   speedx = 0
end if
if shipy > (fullheight - 10) then
   shipy = (fullheight - 10)
   speedy = 0
end if

' Set what part of the full arena will actually be drawn...

cameraleft = shipx - (sw / 2)
cameratop = shipy - (sh / 2)

if cameraleft < 0 then cameraleft = 0
if cameratop < 0 then cameratop = 0
if cameraleft + sw > fullwidth then cameraleft = fullwidth - sw
if cameratop + sh > fullheight then cameratop = fullheight - sh

' Copy that part of the background to the render screen...

x1 = cameraleft
y1 = cameratop
x2 = cameraleft + sw
y2 = cameratop + sh
copyrect x1, y1, x2, y2, 0, 0, sw, sh, 0, fullbackground, virtue

' Render the ship...

set sprite ship, shipx - 10 - cameraleft, shipy - 10 - cameratop
render sprite ship

' Copy the render screen to the console...

copyrect 0, 0, sw, sh, 0, 0, sw, sh, 0, virtue, 0

if keymap key (chr$(27)) then  ' Press escape to end
   disable done
   end
end if

WaitLoop:
if abs(timer - starttime) < 0.02 then goto WaitLoop
goto MainLoop