Help to understand the code

[Guilherme Calabria]

Hi... I have the code bellow, and I need to understand it... I know this script read a file, a hpgl file, it is generates a vector map.
I need to know what some things like 'tp1 = LEFT$(Command,2)' or 'command = REMOVE$(Command,"PU")'

does... I understand C, Java, PHP, Pascal...
thank you for every help!

http://guilherme.plotag.com.br/hpgl.bas

SUB HPGL (Hdlg AS DOUBLE,filename AS STRING)
LOCAL MAXX AS LONG
LOCAL MINX AS LONG
LOCAL MAXY AS LONG
LOCAL MINY AS LONG
LOCAL MX AS LONG
LOCAL MY AS LONG
LOCAL I AS INTEGER,J AS INTEGER
LOCAL FileLen AS LONG
LOCAL tmp AS STRING
LOCAL tp1 AS STRING
LOCAL command AS STRING
LOCAL Crd AS STRING
LOCAL rot AS STRING 'rotation angle
LOCAL sca AS LONG
LOCAL CL AS LONG
LOCAL CPX AS LONG
LOCAL CPY AS LONG



LOCAL pg()AS LONG 'array for page sizes
DIM PG(20,1)
COMBOBOX RESET hDlg, %IDC_COMBOBOX1
COMBOBOX ADD hDlg, %IDC_COMBOBOX1, "0.025"
COMBOBOX ADD hDlg, %IDC_COMBOBOX1, "0.0254"
COMBOBOX SELECT hDlg, %IDC_COMBOBOX1, 1

OPEN filename FOR BINARY AS #1
FileLen = LOF(1)
cl=0
DO
GET$ #1,1,tmp

fileLen=fileLen-1
IF filelen=0 THEN EXIT LOOP
IF tmp=CHR$(&H0A) THEN tmp=""
IF tmp=CHR$(&H0D) THEN tmp=""

IF tmp = ";" THEN 'Command complete
'parse command
tp1 = LEFT$(Command,2)

SELECT CASE tp1
CASE "IN" 'Init
Crd="A":Rot="0"
CASE "PU" ' Pen up
command = REMOVE$(Command,"PU")
IF Crd = "A" THEN
'ignore
ELSE
I = PARSECOUNT(command)
FOR J=1 TO I STEP 2
MX = VAL(PARSE$(command,J))
MY = VAL(PARSE$(command,J+1))
CPX=CPX+MX
CPY=CPY+MY
IF CPX > maxX THEN MaxX = CPX
IF CPX < minX THEN MinX = CPX
IF CPY > MaxY THEN MaxY = CPY
IF CPY < MinY THEN MinY = CPY

NEXT
END IF
CASE "PD" ' Pen Down
command = REMOVE$(Command,"PD")
IF Crd="A" THEN
I = PARSECOUNT(command)
FOR J=1 TO I STEP 2
MX = VAL(PARSE$(command,J))
MY = VAL(PARSE$(command,J+1))
IF mx > maxX THEN MaxX = MX
IF my > maxY THEN MaxY = MY
IF MX < minX THEN MinX = MX
IF MY < MinY THEN MinY = MY
NEXT
ELSEIF Crd="R" THEN
I = PARSECOUNT(command)
FOR J=1 TO I STEP 2
MX = VAL(PARSE$(command,J))
MY = VAL(PARSE$(command,J+1))
CPX=CPX+MX
CPY=CPY+MY
IF CPX > maxX THEN MaxX = CPX
IF CPX < minX THEN MinX = CPX
IF CPY > MaxY THEN MaxY = CPY
IF CPY < MinY THEN MinY = CPY

NEXT


END IF
CASE "PA" ' Plot Absolute
Crd="A"
CASE "PR" ' Plot relative
Crd="R"
CASE "CI" 'circle command
CASE "AA" ' Arc Absolute
CASE "AR" ' Arc Relative
CASE "SP" ' Select Pen
CASE "SC" ' Scale factor
command = REMOVE$(Command,"SC")
sca = VAL(command)
CASE "PG" 'page break
'older plotters Zeros X and Y at and allows continious plotting
'Save current length (Width is a plotter function - ignore)
'add to any stored if required
' should work in both abs and rel cases
MX=Maxx-minx
pg(cl,0)= MX
pg(CL,1)= MaxY-MinY
cl=cl+1
maxx=0
minx=0
maxY=0
minY=0

CASE "RO" 'rotation
command = REMOVE$(Command,"RO")
rot = command
CASE ELSE
'ignore anything else like retangles wedges etc.
END SELECT

command =""
ELSE
command=command + tmp
END IF

LOOP


IF CL=0 THEN 'no pg command
MX=(MaxX-MinX)' use calculated
MY=(MaxY-MinY)
ELSE
mx=0
my=0
FOR I=0 TO CL

MX=MX+pg(I,0)
IF MY < PG(I,1) THEN MY=PG(I,1)
NEXT
'add any bits left
mx=mx+(MaxX-MinX)
IF MY < (MaxY-MinY) THEN MY=(MaxY-MinY)

[Fred Buffington]

st$=LEFT$(Command,2)
puts the first 2 characters as the variable st$ (i think you had tpi or something. so if command="PUT IT HERE" then ST$ would be PU after.



command = REMOVE$(Command,"PU")
This would remove the letters 'PU' from the command variable so,
if COMMAND="PUT IT HERE" originally then it would be 'T IT HERE' after.


BTW, code is much easier to read if you use
{CODE}
before the code
and
{/CODE} after
(but use the square brackets instead of the squiggly brackets)

You should be aware that COMMAND$ is a reserved word and is used to pass information from the command line. This may make the variable command illegal.

[Simon Morgan]

Even if you don't have PowerBASIC, you can look up the commands and what they do in the on-line manual: PB/Win 9.01 manual

[Michael Mattias]

After you look up the stuff in the manual, you will still have a problem because as written the LOCAL variable 'command' never has anything assigned to it... it's null.

[Ralph Bing]

you have to look at the full program

check just before the do you will see where TMP is appended to command

[Michael Mattias]

>check just before the do you will see where TMP is appended to command

I added indents and found it. (also found code is prematurely truncated, it's missing at least an 'end if' and an 'end sub'). .

BTW you CAN 'edit' your own posts to insert the code tags.

MCM

[Guilherme Calabria]

...

thank you for the tips Fred Buffington and the manual Simon Morgan
I will check there...
Michael Mattias did you see the full code at:

http://guilherme.plotag.com.br/hpgl.bas

the missing things will be a problem to convert the function HPGL to another language?