Post processor files are written in the Lua macro language. See http://www.lua.org and  http://lua-users.org/wiki/LuaDirectory
The post is event based. Each event has a function associated with it.

The available events are:

function OnAbout(event)

Occurs when the post details are displayed.
The event is a wxOptionsEvent(see plugin documentation). A simple about would look something like this:
function OnAbout(event)
ctrl = event:GetTextCtrl()
ctrl:AppendText("My post processor\n")
ctrl:AppendText("Another line\nYet another line")
end

function OnInit()

Occurs when the output file is opened.
Set the variable ‘bigarcs’ to 1 if you don’t want arcs to be output as quadrants * DEPRECATED * see SetOptions instead
Set the variable ‘minarcsize’ to the minimum arc size in millimetres. If arcs are less than this size they will be turned into moves instead. Default value is 0.05mm

function OnNewLine()

Whenever a new line is written to the output file

function OnFinish()

Occurs just before the output file is closed.

function OnRapid()

Rapid linear move

function OnMove()

Linear move at feedrate

function OnArc()

Arc/helical move. See the arcasmoves() function if your machine cannot handle arcs.

function OnDrill()

drill

function OnDrillStart()

Called just before drilling, after the toolchange.

function OnDrillEnd()

Called after drilling is finished, before OnNewOperation()

function OnAutoTap()

Tap with a tapmatic type automatic tapping head

function OnRigidTap()

Tap with a rigid tapping head

function OnTapStart()

Called just before tapping, after the toolchange.

function OnTapEnd()

Called after tapping is finished, before OnNewOperation()

function OnPenUp()

Z axis moves upward. Can be used to turn a plasma/laser off

function OnPenDown()

Z axis moves downwards. Can be used to turn a plasma/laser on

function OnSetFeed()

Feed rate change

function OnToolChange()

Tool change

function OnNewOperation()

Occurs when a new operation is started

function OnNewPart()

When a new part is started

function OnSpindleCW()

Turn the spindle on clockwise

function OnSpindleCCW()

Turn the spindle on anticlockwise

function OnSpindleOff()

Turn the spindle off

function OnSpindleChanged()

The spindle speed has changed

function OnFloodOn()

Turn flood coolant on

function OnMistOn()

Turn mist coolant on

function OnCoolantOff()

Turn coolant off

function OnComment()

Output a comment to the g-code file. See commenttext variable below.

function OnNewEntity()

Called at the start of a new cut. This occurs just before moving to the start of the cut. See entitylength and entityclosed variables below.

function OnFileOpen()

Called just before the output file is opened. You can change the values of the fileName and filePath variables if you wish to save to a different file.

function OnFileClosed()

Called after the g-code file has been saved. Could be used to trigger an external application to execute the code.
In each event the following standard functions are available. Note that they are in the post namespace so each should be preceded by 'post.'.
For example post.Warning("This is a warning").

Message(text,[text],...)

All parameters are combined into one string and displayed on the progress window.

Warning(text,[text],...)

All parameters are combined into one string and displayed on the progress window as a warning.

Error(text,[text],...)

All parameters are combined into one string and displayed on the progress window as an error.

Text(text,[text],...)

All parameters are output to the file. Line numbers are added to the start of each line and empty lines are ignored

TextDirect(text,[text],...)

All parameters are output to the file. The text is not processed in any way. No line numbers are added.

ModalText(text)

The text is output to the file unless the last call to modaltext contained the same text
Here is an example:
modaltext(“G0”) - “G0” is output (the first call to modaltext() always outputs the code)
modaltext(“G0”) - nothing is output because the previous call was “G0”
modaltext(“G1”) - “G1” is output because the previous call wasn't “G1”
modaltext(“G1”) - nothing is output because the previous call was “G1”
modaltext(“G83”) - “G83” is output because the previous call wasn't “G83”

CancelModaltext()

The next call to modaltext will always output the text to the file. It is functionally equivalent to modaltext(“”)

Number(number, format)

Output the number in the format specified by the format string. Number can be any valid numeric expression
The format string defines the number of leading and trailing zeros.
The character '0' means that that digit must be output even if it is a leading or trailing zero.
The character '#' means that the digit will be output if it is not a leading or trailing zero.
A leading + indicated that the sigh should always be shown.
For instance Number(2.5 "+0000.00") will output ‘+0002.50', Number (2.56 "0.#") will output '2.6' and Number(123.45 "0.") will output '123'
Returns: The number as it was formatted. For instance:
post.Number(123.456789,”0.00”)
would output “123.46” and return the number 123.46. This is useful for incremental posts.

FormatNumber(number, format)

Format a number using the format specified by the format string.
Returns: A string containing the formatted number and the number as it was formatted.
For example a,b = post.FormatNumber(123.456,”+0.0”) would return:
a = “+123.5”
b = 123.5
a = post.FormatNumber(123.456,”+0.0”) would return:
a = “+123.5”

ModalNumber(text, number, format)

Text and number is output to the file if the number is different to the last time ModalNumber was called with the same text. For example the following code:
ModalNumber " X" 10 "0.0##"
ModalNumber " Y" 20 "0.0##"
ModalNumber " X" 10 "0.0##"
ModalNumber " Y" 21 "0.0##"
ModalNumber " Y" 21 "0.0##"
will output: ' X10 Y20 Y21'
Returns: The number as it was formatted. If the number was not output the return value is the value as it would have been output.

NonModalNumber(text, number, format)

like modalnumber() but text and number are always output. This keeps track of modality if you wish to use modalnumber somewhere else.
Returns: The number as it was formatted.

CancelModalNumbers()

This resets all modal numbers.
for example the following code
modalnumber " X" 10 "0.0##"
cancelmodalnumbers()
modalnumber " X" 10 "0.0##"
will output ‘ X10 X10’

Eol()

Write an end of line to the file. This equivalent to text("\n")

SetCommentChars(source chars, replace chars)

if any source char is found in a filename or post name it is replaced with the equivalent replace char. For instance if your post is called "mypost(1).post"
then the following code:
post.SetCommentChars ("()", "[]")
text “(postname)”
will output 'mypost[1].post' to the file.

ArcAsMoves(Tolerance)

Perform the current arc as a series of short linear moves. This should only be called from the onArc() event.
Tolerance is the maximum deviation in millimetres from a true arc.All other parameters are optional. Reducing Tolerance increases the number of line segments generated.

SetEncoding(Encoding)

Set the file encoding. This overrides the option in options->machine->post processor and would normally be called from function OnInit()
Encoding is one of :


wx.wxFONTENCODING_SYSTEM	system default
wx.wxFONTENCODING_DEFAULT	current default encoding
wx.wxFONTENCODING_ISO8859_1	West European (Latin1)
wx.wxFONTENCODING_ISO8859_2	Central and East European (Latin2)
wx.wxFONTENCODING_ISO8859_3	Esperanto (Latin3)
wx.wxFONTENCODING_ISO8859_4	Baltic (old) (Latin4)
wx.wxFONTENCODING_ISO8859_5	Cyrillic
wx.wxFONTENCODING_ISO8859_6	Arabic
wx.wxFONTENCODING_ISO8859_7	Greek
wx.wxFONTENCODING_ISO8859_8	Hebrew
wx.wxFONTENCODING_ISO8859_9	Turkish (Latin5)
wx.wxFONTENCODING_ISO8859_10	Variation of Latin4 (Latin6)
wx.wxFONTENCODING_ISO8859_11	Thai
wx.wxFONTENCODING_ISO8859_13	Baltic (Latin7)
wx.wxFONTENCODING_ISO8859_14	Latin8
wx.wxFONTENCODING_ISO8859_15	Latin9 (a.k.a. Latin0, includes euro)
wx.wxFONTENCODING_KOI8	KOI8 Russian
wx.wxFONTENCODING_KOI8_U	KOI8 Ukrainian
wx.wxFONTENCODING_ALTERNATIVE	same as MS-DOS CP866
wx.wxFONTENCODING_BULGARIAN	used under Linux in Bulgaria
wx.wxFONTENCODING_CP437	original MS-DOS codepage
wx.wxFONTENCODING_CP850	CP437 merged with Latin1
wx.wxFONTENCODING_CP852	CP437 merged with Latin2
wx.wxFONTENCODING_CP855	another cyrillic encoding
wx.wxFONTENCODING_CP866	and another one and for Windows
wx.wxFONTENCODING_CP874	WinThai
wx.wxFONTENCODING_CP932	Japanese (shift-JIS)
wx.wxFONTENCODING_CP936	Chinese simplified (GB)
wx.wxFONTENCODING_CP949	Korean (Hangul charset)
wx.wxFONTENCODING_CP950	Chinese (traditional - Big5)
wx.wxFONTENCODING_CP1250	WinLatin2
wx.wxFONTENCODING_CP1251	WinCyrillic
wx.wxFONTENCODING_CP1252	WinLatin1
wx.wxFONTENCODING_CP1253	WinGreek (8859-7)
wx.wxFONTENCODING_CP1254	WinTurkish
wx.wxFONTENCODING_CP1255	WinHebrew
wx.wxFONTENCODING_CP1256	WinArabic
wx.wxFONTENCODING_CP1257	WinBaltic (same as Latin 7)
wx.wxFONTENCODING_UTF7	UTF-7 Unicode encoding
wx.wxFONTENCODING_UTF8	UTF-8 Unicode encoding
wx.wxFONTENCODING_EUC_JP	Extended Unix Codepage for Japanese
wx.wxFONTENCODING_UTF16BE	UTF-16 Big Endian Unicode encoding
wx.wxFONTENCODING_UTF16LE	UTF-16 Little Endian Unicode encoding
wx.wxFONTENCODING_UTF32BE	UTF-32 Big Endian Unicode encoding
wx.wxFONTENCODING_UTF32LE	UTF-32 Little Endian Unicode encoding

The following functions should only be called at post load time.

This means that they should be outside any other function definition.

DefineVariable(varName,units,min,max)

Define a variable name for use in the ‘set variable’ dialog.
varName = variable name
units. One of the following: sc.unitTEXT, sc.unitLINEAR, sc.unitANGULAR, sc.unitFEED, sc.unitRPM, sc.unitTIME, sc.unitPERCENT, sc.unitPITCH,
sc.unit0DECPLACE, sc.unit1DECPLACE, sc.unit2DECPLACE, ,sc.unit3DECPLACE, sc.unit4DECPLACE note the unitxDECPLACE units display
a number without units with a precision of the given number of decimal places
min minimum value (ignored for text)
max maximum value (ignored for text)

DefineCustomOption(caption,varName,units,min,max, default)

Adds an option to the post options.
caption is a label that is displayed next to the input box.
The rest of the syntax is as DefineVariable above.

ShowCustomOptions(caption)

Show an options dialog containing the options defined using DefineOption.
Caption is displayed in the dialog box title.
If no options have been defined this function has no effect.

DefineCustomToolParam(toolClass,caption,varName,units,default,min,max)

Adds an extra parameter to a tool definition.
toolClass is the tool class name. See the toolClass variable for a description of tool classes
default is the default value. Note that values are always in METRIC for linear units, RADIANS for angular units and a decimal fraction for percentage e.g 0.1 = 10%
The rest of the syntax is as DefineVariable above.

ForceExtension(extension)

Force the file extension. Extension should not include a leading dot. This overrides the user’s selection
e.g post.ForceExtension(“tap”)

SetOptions(option)

Set an option. The available options are:

• post.DISABLE_TOOLCHANGE Disable tool change options in SheetCam. The post and machine handle all tool change moves
• post.ARC_SEGMENTS Arcs should never exceed 180 degree
• post.DISABLE_ROTARY Disable rotary cutting options
• post.DISABLE_JET Disable jet cutting options

To combine options add them. For instance:
Post.SetOptions(post.DISABLE_TOOLCHANGE + post.DISABLE_ROTARY)

The following predefined variables are available:

currentX,currentY,currentZ

Current X,Y,Z coordinates.

endX,endY,endZ

X,Y,Z coordinates to move to. These variables are only valid for movement events.

arcAngle

Angle of current circular move in radians. Positive = clockwise. 0 = 12 o'clock. This variable is only valid for circular moves

arcCentreX,arcCentreY

Center X,Y coordinates of current circular move. This variable is only valid for circular moves

plungeSafety

Safe clearance above the cut start. Rapids should be down to this then move at feed rate down to the cut start.

drillStart

drillling and tapping start depth

drillZ

drill and tapping depth

drillPeck

Drill peck depth

drillRetract

Drill retract amount

safeZ

Rapid height

materialTop

Z coordinate of material top (always 0)

feedRate

Current feed rate

plungeRate

Plunge rate for this tool. Use for verification purposes only - feedrate is updated to reflect plunge rate when plunging.

inch

This variable is always 1/25.4

metric

This variable is always 1

scale

for inch post output this variable is 1/25.4 otherwise it is 1

tool

Current tool number

nextTool

The number of the next tool to be pre-selected. -1 if there are no more tools needed

line

Current line number

spindleSpeed

Current spindle speed

fileName

G-code file name

fileNameOnly

G-code file name without path

filePath

G-code file path

partName

Part name

toolName

Current tool name

operationName

Current operation name

date

date that post processing was started

time

time that post processing was started

postName

Post processor file name

preheat

preheat delay (flame tool only)

pierceDelay

pierce delay (jet tool only)

pierceHeight

pierce height (jet tool only)

cutHeight

cut height (jet tool only)

endDelay

end of cut delay (jet tool only)

power

Laser power (laser and waterjet tools only)

materialX1, materialY1

Bottom left coordinates of material

materialX2, materialY2

Top right of material

materialThick

Material thickness

materialHeight

Height of material above the table

toolDia

Tool diameter

toolLength

Tool length

toolFluteLength

Tool flute length

toolOffset

Tool length offset

toolAngle

Tool V angle or drill point angle in radians (only valid for V cutters or drills). Multiply by 57.29577951308 to convert to degrees

toolType DEPRECATED - use toolClass instead

-1 = unknown
0=mill/router
1=drill
2=V cutter
3=plasma
4=insert g-code
5=automatic tap
6=rigid tap
7=flame
8=water
9=laser

toolClass

MillTool=mill/router
DrillTool=drill
VTool=V cutter
PlasmaTool=plasma
CodeTool=insert g-code
TapHeadTooll=automatic tap
TapTool=rigid tap
FlameTool=flame
WaterTool=water
LaserTool=laser
ThreadMillTool=Thread mill
MarkerTool=Plate marker

operationClass

One of the following:

VariableOperation
MoveOperation
CodeOperation
JetOperation
DrillOperation
TapOperation
ContourOperation
PocketOperation
ZigzagPocketOperation
ThreadMillOperation

tapPitch

Tapping feed per rev. Only used by the autotap() and rigidtap() events

underFeed

Tapping underfeed. Only used by the autotap() and rigidtap() events. 0.5 = 50%, 1= 100% etc

tapTravel

Tapping head axial travel. Only used by autotap() event

reverseMult

Tapping head reverse multiplier. Only used by autotap() event

commentText

Text for the comment() event

entityLength

length of the next cut path

entityClosed

1 if the cut path is closed, 0 if it is open.

leadinType

Defines if this is a leadin/leadout
0: Not a leadin/leadout.
1: A leadin.
2: A leadout.

spindleDir

-1 = CCW, 0 = off, 1 = CW

partIndex

the index(starting from 0) of the current part

operationIndex

the index(starting from 0) of the current operation

cutDepth

The depth of cut. 0 if the tool does not exist or this operation does not use a tool.

Variables

All of SheetCam's internal variables are available in the var namespace. For instance :

var.ClampClearanceHeight would give the material thickness. You can see all of the available variables using the variable monitor (View->variable monitor)

The following Lua libraries are included:

math. See http://lua-users.org/wiki/MathLibraryTutorial for more details. This library has been extended to add the following functions:

math.hypot(x,y). This is equivalent to math.sqrt((x*x) + (y*y))
math.toint(n). Returns the integer value of n.

string. See http://lua-users.org/wiki/StringsTutorial for more details.

os Seehttp://lua-users.org/wiki/OsLibraryTutorial for more details

Also all of the wxLua plugin functions are available. See the plugin documentation.