Tài liệu Understanding HPGL pptx

To produce a sample HPGL file, configure a CAD package to plot to file using an HPGL driver possibly called "HP Plotter" or given a specific model number, such as HP7220 or HP7586.. Even

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Understanding HPGL

Hewlett-Packard has found itself in the fortunate position of having creating two de facto standards

for output devices: HPGL (short for Hewlett-Packard Graphics Language) and PCL, short for Printer Control Language Although HPGL was intended for HP's line of pen plotters, variants have found their way into inkjet and laser printers PCL, on the other hand, is strictly used by HP for its raster devices and is very slowly loosing favor to PostScript and Windows-based direct-GDI

A Brief History of HPGL

HPGL is a command set embedded in the ROM of pen plotters to help reduce the work required by applications programmers to create plotted output HPGL uses two-letter mnemonics as instructions for drawing lines, circles, text, and simple symbols HPGL has evolved over the years as HP added features to its line of pen, electrostatic, inkjet, and laser plotters and printers

However, there is one primary drawback to HPGL: it is bulkier than other plotting languages, which means it takes longer to transmit an HPGL plot file than, say, a Houston Instruments' DM/PL (short for digital microprocessor plotting language) plot file To overcome the limitation, Hewlett-Packard in 1988 introduced HPGL/2, which featured

"polyline encoding," a form of data compression that reduces the plot file size and, hence, transmission time by two-thirds

With HPGL being the de facto plotting standard, competitors inevitably include HPGL or some similarly-named dialect in their plotter products In addition, HPGL has become a form of CAD drawing translation of last resort, since all CAD packages produce HPGL files and several read the format

Coordinate Systems

One irritant to HPGL is that there are two different coordinate systems in use Small-format plotters, including A- and B-size plotters, locate the origin at the lower-left corner; large-format plotters, including D- and E-size plotters, located the origin at the center of the media

TIP: HPGL uses the plu (short for plotter units) as its form of measurement There are 40 plu per

millimeter and 1,016 plu in one inch

All plotting languages have two forms of limits: (1) hard limits; and (2) soft limits The hard limits are the limits beyond which the plotter cannot plot due to physical constraints The soft limits are usually imposed by the application software generating the plot file Any part

of the drawing extending beyond the limits (hard or soft) is clipped (is not be plotted) HPGL names the plot extents as P1 (the lower-left corner) and P2, the upper-right corner

Reading An HPGL Plot File

A typical HPGL plot file consists mostly of ASCII characters with some control codes thrown in You can read the file with any text editor Since the plot files tend to be written

as one long line (no CR or LF), it is helpful to have a text editor with no limitation on line length

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To produce a sample HPGL file, configure a CAD package to plot to file using an HPGL driver (possibly called "HP Plotter" or given a specific model number, such as HP7220 or HP7586) Create a very simple drawing (a couple of lines), then plot the drawing to disk When you load a plot file into the text editor, it looks something like this:

Plot initialization data:

[Esc].(;.I81;;17:[Esc].N;19:IN;SC;PU;PU;SP1;LT;VS36;

Plot data:

PA12345,4567;PD;PA-2345;6789; et cetera

Plot termination data:

PU;PA0,0;SP;EC;PG1;EC1;OE;

Decoding the HPGL Code

HPGL consists of two kinds of instructions:

• 1 HPGL instructions

• 2 Device-control instructions (or DCI, for short)

The most typical HPGL instruction is:

PA1234,5678;

The PA instruction moves the pen to absolute position (1234,5678) in plu coordinates The instruction has four parts to its syntax: PA is an HPGL command (in this case, to move the pen)

 1234 and 5678 are parameters (in this case, absolute coordinates)

 , a separator (the comma) between two or more parameters

 ; and a terminator (the semi-colon)

PA All HPGL instructions start with a two-letter mnemonic For example, PA is the

abbreviation for Pen Absolute, a pen positioning command Other common command mnemonics include:

• PD for pen down

• PU for pen up

• SP for select pen

• VS for velocity speed

1234 and 5678 Most HPGL instructions include one or more parameters to modify their

meaning Here, 1234 and 5678 are the absolute pen coordinates in plu Parameters of other instructions are the pen number and plotter speed

TIP: To use the default parameter of an instruction, simply leave out the parameter value

, (separator) When an instruction uses more than one parameter, HPGL wants them

; (terminator) To indicate the end of the instruction, you have the option of using a

semi-colon ( ; ) or nothing at all

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TIP: Use the semi-colon when you want to make the plot file legible to humans; use no terminator

to significantly reduce transmission time and file size

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Device-Control Instructions

HPGL uses device-control instructions to set up the plotter's hardware These instructions set up communications between the CAD software and the plotter, return plotter status data, reset the plotter, et cetera

Device-control instructions (DCI, for short) begin with the escape character (ASCII 27, or

1B in hex) shown as [Esc] in this tutorial Text editors often show Escape as a left arrow

( <- ) or as Ctrl-Bracket ( ^[ ) A typical HP device-control instruction looks like this:

[Esc].N0;19:

The purpose of this DCI is to specify the Xoff (short for transmission off) trigger character, which tells the plotter which ASCII character the CAD software expects to receive as the Xoff character, as follows:

• [Esc] (Escape followed by period) Alerts the plotter that a device-control instruction

follows

• N This DCI specifies the Xoff handshake character.

• 0 Value of intercharacter delay

TIP: The default value is zero; default DCI values can be omitted, as in [Esc].N;19;

• ; (separator) Separates DCI parameters

TIP: The separator is optional for DCIs that don't use parameters

• 19 The ASCII value of the Xoff character ASCII 19 is DC3, a commonly-used value.

• : (terminator) Terminates the DCI

TIP: DCIs with parameters must end with the colon ( : ); the terminator is optional for DCIs

without parameters

Initializing the HPGL Plot File

A typical HPGL plot file consists mostly of ASCII characters with some control codes thrown in The plot initialization data (in this case, generated by AutoCAD R11) looks something like this:

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[Esc].(; instructs the plotter to interpret data as HPGL and DCI instructions, rather than

plotting the data stream as literal text characters This DCI has no parameters; [Esc].Y is an alternative provided by HPGL

[Esc].I81;;17: sets the parameters for Xon-Xoff handshake mode, with the following

parameters:

• 81; (Xoff threshold level) When 81 bytes remain free in the plotter buffer, the plotter sends

the Xoff instruction to the CAD software Xoff tells the CAD software to stop sending data, otherwise the plotter buffer fills up and data is lost TIP: If the byte size is too large, HPGL automatically reduces the size to one byte smaller than the plotterþs logical I/O buffer size; use [Esc].Sn: to find the size of the buffer

• ; (ommited parameter) Since the next parameter is missing, the plotter is able to differentiate

between Xoff/Xon and Enq/Ack protocols TIP: You can substitute 0 (zero) for the ommited parameter

• 17: (Xon trigger character) After the CAD software stops sending data to the plotter, the

plotter uses the Xon trigger character to tell the software to continue sending data ASCII 17

is DC3, the standard value TIP: You can specify any decimal ASCII value between 0 and

126 and use as many as ten characters

[Esc].N;19: was described earlier

IN; (INitialize) Resets most of the plotter's functions to default settings, some of which

follow:

• Set linetype to solid (equivalent HPGL instruction is LT0;)

• Set plotting mode to absolute (PA;)

• Set chord angle to 5 degrees (CT;)

• Turn off user scaling (SC;)

• Recognize all HPGL errors (IM;)

• Set input window to hardclip limits (IW;)

• Set units to metric and pen width to 0.3mm (PT;)

• Lift pen (PU;) and move it within 600 plu of hardclip limits

TIP: Settings made on the plotter's front panel are not reset

TIP: Recall that the semi-colon ( ; ) terminator is optional

SC; (SCale) Scale the coordinate system to the plot's extents, P1 and P2; the default is no

scale (the CAD software handles the scaling)

PU; (Pen Up) Lifts the pen; optionally moves the pen to a new location

SP1; (Select Pen) Selects a pen, #1 in this case

TIP: HPGL automatically returns the current pen to its holder at the end of a plot

LT; (Line Type) Selects the linetype and pattern length; the default is continuous lines (the

CAD software handles the linetype generation)

VS36; (Velocity Select) Selects the pen speed in cm/sec; optionally selects the pen by

number

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TIP: The pen speed is sometimes overruled by the setting of the pen carousel HP suggests using a

slower speed to create a slightly thicker line (but at the expense of longer plot time)

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HP-GL/2 History

HP-GL/2 was added to the PCL language in PCL Level 5, for LaserJet III family printers and is supported in LaserJet 4 family printers with PCL Level 5 Enhanced To print in HP-GL/2 you are required to leave the PCL environment and enter the HP-GL/2 environment Switching into and out

of HP-GL/2 requires only a few commands, and cannot be done through the front menu panel Some software applications may easily switch between the two modes as needed without affecting performance

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Learning HP-GL/2

The best way to learn HP-GL/2 is to read the "Introduction to HP-GL/2 Graphics" in the PCL 5 Printer Language Technical Reference Manual for an overview of HP-GL/2 Then find the specific commands you need in subsequent chapters Reading through the examples, then trying to print them using a text editor or programming language is the best way to learn HP-GL/2

LEGEND: Ec = [Ctrl] [P] [Esc] in DOS EDIT

EcE Resets the printer

SP1; Selects pen number 1 (black) Even though there is no physical pen, the SP command must

be used to enable printing

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SI width, height; or SI;

SP1; Selects pen number 1, (black) Even though there is no physical pen,

the SP command must be used to enable printing

PA700,2000;SI1,1.5;LBPrint#; Moves to (700,2000); specifies an absolute character size of 1

cm wide by 1.5 cm high; prints the word "Print"

PA4000,2000;SI1,1.5;LBPrint#; Moves the pen to (4000,2000) and specifies a character size of

1 cm by 1.5 cm; prints the word "Print"

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Ec%0B Enters HP-GL/2 mode

IN; Initializes HP-GL/2 mode

SP1; Selects pen number 1, (black) Even though there is no physical pen, the SP command must

PA3000,3000; Specifies absolute plotting and moves to location (3000,3000)

FT3,400,45;RR1000,1000;

ER1000,1000; Specifies a fill type of number 3 (parallel lines), with each line 400 plotter units (plu) apart and set at a 45 degree angle RR fills a rectangle using the current pen location as the lower left corner, and a point 1000 plu to the right and 1000 plu up as the upper right corner The ER edges the same rectangle just filled

PR1000,0;FT4,400,45;RR1000,

1000;ER1000,1000; Moves 1000 plu to the right, andselects fill type 4 (cross-hatch); then draws a rectangle the same size as the first one, and fills it with the cross-hatch pattern just specified, then edges it with the ER command

PR1000,0;FT3,400,45;

RR1000,1000;ER1000,1000; Moves to the right another 1000 plu, and creates another rectangle of the same size, then fills this one with the number 3 fill pattern again Then edges the rectangle just specified

PA3000,1500;AC3000,1500;

RR1000,1000;ER1000,1000; Moves the pen to absolute position (3000,1500), and moves the anchor corner to location (3000,1500) Fills a rectangle with the fill pattern selected (number 3 from the command above), and

edges it

PA4000,1500;AC4000,1500;

FT4,400,45;RR1000,1000, ER1000,1000; Moves to location (4000,1500) andspecifies the

location as the anchor corner Selects fill type number 4 again, then fills, and edges a rectangle

EcE Sends a reset to end the job and eject the page

NOTE Due to space limitations these lines of code appear on more than one line When entered into the DOS editor they should appear on one line

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NOTE The Bezier command is not supported in any printers prior to the HP LaserJet 4 printer

EcE Resets the Printer

The other three control points for the second curve are (4064,8128), (7112,7620), and (7112,2032)

Ec%0A Enters PCL mode

This command, BR or Bezier Relative , draws bezier curves using relative coordinates This

command uses the current pen position as the first control point, and specifies the other three control points as relative increments from the first point For more information see the PCL 5 Printer Language Technical Reference Manual

NOTE The Bezier command is not supported on printers prior to the LaserJet

4 printer

LEGEND: Ec = [Ctrl] [P] Esc] in DOS EDIT

Ec%0B Enters HP-GL/2 mode

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IN; Initializes HP-GL/2 mode

Changing Radii and Line Types in Circles

The Line Type command specifies a line pattern to be used when drawing lines You can specify the line type, pattern length and the mode The line type specifies a particular pattern, the pattern length specifies the length of one complete line pattern, and mode specifies how the values of the pattern length parameter are interpreted For more information see the PCL 5 Printer Language Technical Reference Manual

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SP1; Selects pen number 1, (black) Even though there is no physical pen, the SP command must

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differences in appearance between chord angles on circles For more

information see the PCL 5 Printer Language Technical Reference Manual

SP1; Selects pen number 1 (black) Even though there is no physical pen, the

SP command must be used to enable printing

SC-3000,3000,-2000,2000,1; Specifies a scaling mode, making P1 equal

to (-3000,-2000) user units and P2 equal to (3000,2000) user units With

isotropic scaling specified

PA-1700,2000;CI750,45; Specifies absolute plotting and moves to

(-1700,2000), the center of the circle, to be drawn Draws a circle with a radius of

750 user-units and a chord angle of 45 degrees

PA300,2000;CI750,30; Specifies absolute plotting and moves to (300,2000)

to draw another circle This circle is drawn with a radius of 750 user-units, and a chord angle of 30 degrees

PA-1700,-200;CI750,15; Specifies absolute plotting and moves to (-1700,-200) the center point of a third circle This circle is drawn with a radius of 750 user-units, and a chord angle of 15 degrees

PA300,-200;ci750; Specifies absolute plotting and moves to (300,-200),

the center of the fourth circle Draws this circle with a radius of 750 user-units and the default chord angle of 5 degrees

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Subroutine to Print the Arrow Image

-Creating and Printing a Raster Fill Pattern

=========================================

The Raster Fill ( RF ) Command is used to define a fill pattern to be used in other fill commands The RF command does not select a fill type, it defines a user created fill type that can then be selected using the Fill Type ( FT )

command, with a type parameter of 11 and the corresponding raster fill index number for the second parameter For example FT11,3; for the index number 3

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For more information see the PCL 5 Printer Language Technical Reference

Manual The syntax for the RF command is as follows:

RF index,width,height,pen number pen number; or RF index; or RF;

Raster Fill Pattern Parameters

Index Specifies the index number of the pattern being defined

Width and Height Specifies the width and height in pixels of the pattern being defined

Pen Number Represents a pixel in the pattern being defined and indicates

its color, black (>0) or white (0) This parameter defines pixels left to right, top

to bottom, and the total number of pen number parameters should be equal to

the width times the height parameter For example, to define a pattern that is 8 x16 pixels, you need 128 pen number parameters If not all pen parameters are specified, the remainder parameters default to zeros (white) The pattern that is created is printed in rows parallel to the plotter-units X-axis

Raster Fill Pattern Program

SP1; Selects pen number 1, (black) Even though there is no physical pen,

the SP command must be used to enable printing

edges the polygon just drawn

Ec%0A Enters the PCL mode

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-

-Default Settings for The HP-GL/2 Environment

=========================================

When you enter the HP-GL/2 environment for the first time, all settings are at their default When you exit HP-GL/2 to send other PCL commands then re-enter HP-GL/2, most variables retain their previous values However, the following changes in the PCL environment can affect the HP-GL/2

environment

Tiêu đề	Understanding Hpgl
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