'
'      Screen tutorial #02 - Screen Display and Screen Offset  
'
'
' Open one heck of a big screen! 
'
Screen Open 0,1000,800,4,Lowres
'
'Display a matrix of 320x200 of the screen and position the X start
'of the screen a little to the right.
'
Screen Display 0,140,,320,200
'
'Print text onto the screen. At some weird x,y co-ordinates! 
'
Print At(0,0);"Top Left of a very big screen"
Print At(0,87);"Bottom Left";
Print At(111,0);"Top Right"
Print At(107,87);"Bottom Right";
'
' Fill the main area of the screen full of characters
'
Locate 0,2
For A=0 To 83
   For B=0 To 55
      Print Chr$(A+32);" ";
   Next B
   Print 
Next A
'
' Tell user they can scroll around the screen
'
Pen 3
Locate 5,5
Print " Move the screen using "
Locate 5,6
Print "    the arrow keys     "
'
' Check up, down, left and right keys. If one is pressed change the
' screen offset. 
'
Do 
   TAKE_KEY:
   A$=Inkey$ : If A$="" Then Goto TAKE_KEY
   S=Scancode
'
' Checks for up arrow key. (Change -8 to -4,-2 or -1)
'
   If S=76
      If SYO<>0
         SYO=SYO-8
      End If 
   Else 
      If S=77 : Rem       Check for down arrow 
         If SYO<>520
            SYO=SYO+8
         End If 
      Else 
         If S=79 : Rem    Check for left arrow  
            If SXO<>0
               SXO=SXO-8
            End If 
         Else 
            If S=78 : Rem Check for down arrow   
               If SXO<>640
                  SXO=SXO+8
               End If 
            End If 
         End If 
      End If 
   End If 
   Wait Vbl 
'
' Set screen to its new offset. Remember, it's a port hole over the whole
' screen.
   Screen Offset 0,SXO,SYO
Loop