3 steps to building a scrolling LED screen

I think I have it commented enough to follow easily

_Title "Building a Scrolling LED Screen" ' b+ 2021-05-08
Screen _NewImage(1200, 160, 32)
_Delay .25 'give screen time to load
_ScreenMove _Middle 'and center screen

'scroll some text
Text$ = "Try scrolling me for awhile until you got it, then press a key...  "
lenText = Len(Text$)
startTextPos = 1
'put text in sign 15 chars wide in middle of screen print the message moving down 1 character evey frame
_Title "Building a Scrolling LED Screen: Step 1 get some code to scroll your message in middle of screen."
Do
   k$ = InKey$
   Cls
   ' two pieces of text? when get to end of text will have less than 15 chars to fill sign so get remainder from front
   len1 = lenText - startTextPos
   If len1 < 15 Then len2 = 15 - len1 Else len1 = 15: len2 = 0
   ' locate at middle of screen for 15 char long sign
   _PrintString ((1200 - 15 * 8) / 2, (160 / 2) - 8), Mid$(Text$, startTextPos, len1) + Mid$(Text$, 1, len2)
   startTextPos = startTextPos + 1
   If startTextPos > lenText Then startTextPos = 1
   _Display ' no blinking when clear screen so often
   _Limit 5 ' slow down to see scroll
Loop Until Len(k$)

' OK  now for the enLARGE M E N T  using _PutImage
' our little sign is 16 pixels high and 8 * 15 chars pixels wide = 120
Dim sign As Long
sign = _NewImage(120, 16, 32) ' we will store the print image here

' _PUTIMAGE [STEP] [(dx1, dy1)-[STEP][(dx2, dy2)]][, sourceHandle&][, destHandle&][, ][STEP][(sx1, sy1)[-STEP][(sx2, sy2)]][_SMOOTH]
' use same pixel location to _printString as for _PutImage Source rectangle ie (sx1, sy1), -step( sign width and height)

' test screen capture with _putimage and then blowup with _putimage
'_PutImage , 0, sign, ((1200 - 15 * 8) / 2, (160 / 2) - 8)-Step(119, 15)
'Cls
'_PutImage , sign, 0 ' stretch to whole screen
'_Display

'now that that works do it on the move

' about here I resized the screen to 1200 x 160 to make the text scalable X's 10 ie 120 x 10 wide and 16 x 10 high
_Title "Building a Scrolling LED Screen: Step 2 Blow it up by using _PutImage twice once to capture, then to expand"
k$ = ""
Do
   k$ = InKey$
   Cls
   ' two pieces of text? when get to end of text will have less than 15 chars to fill sign so get remainder from front
   len1 = lenText - startTextPos
   If len1 < 15 Then len2 = 15 - len1 Else len1 = 15: len2 = 0
   ' locate at middle of screen for 15 char long sign
   _PrintString ((1200 - 15 * 8) / 2, (160 / 2) - 8), Mid$(Text$, startTextPos, len1) + Mid$(Text$, 1, len2)
   _PutImage , 0, sign, ((1200 - 15 * 8) / 2, (160 / 2) - 8)-Step(119, 15)

   Cls
   _PutImage , sign, 0 ' stretch to whole screen
   _Display ' no blinking when clear screen so often
   _Limit 5 ' slow down to see scroll
   startTextPos = startTextPos + 1
   If startTextPos > lenText Then startTextPos = 1
Loop Until Len(k$)



' now for a mask just draw a grid test grid draw here
'For x = 0 To _Width Step 10 ' verticals
'  Line (x, 0)-(x + 3, _Height), &HFF000000, BF
'Next
'For y = 0 To _Height Step 10
'  Line (0, y)-(_Width, y + 3), &HFF000000, BF
'Next



_Title "Building a Scrolling LED Screen: Step 3 Mask or Cover the thing with a grid or grate."
' here is the whole code not including all setup variables from above
k$ = ""
Do
   k$ = InKey$
   Cls
   ' two pieces of text? when get to end of text will have less than 15 chars to fill sign so get remainder from front
   len1 = lenText - startTextPos
   If len1 < 15 Then len2 = 15 - len1 Else len1 = 15: len2 = 0
   ' locate at middle of screen for 15 char long sign
   _PrintString ((1200 - 15 * 8) / 2, (160 / 2) - 8), Mid$(Text$, startTextPos, len1) + Mid$(Text$, 1, len2)
   _PutImage , 0, sign, ((1200 - 15 * 8) / 2, (160 / 2) - 8)-Step(119, 15)

   Cls
   _PutImage , sign, 0 ' stretch to whole screen

   ' now for a mask just draw a grid best to draw this and copy and layover screen as another layer
   ' here QB64 is fast evough to redarw each time
   For x = 0 To _Width Step 10 ' verticals
       Line (x, 0)-(x + 3, _Height), &HFF000000, BF
   Next
   For y = 0 To _Height Step 10
       Line (0, y)-(_Width, y + 3), &HFF000000, BF
   Next

   _Display ' no blinking when clear screen so often
   _Limit 5 ' slow down to see scroll
   startTextPos = startTextPos + 1
   If startTextPos > lenText Then startTextPos = 1
Loop Until Len(k$)




Note: how the whole code block at the end is only a few dozen lines long and does it all!