Part II 17 An Introduction to HP-GL/2 Vector Graphics The PCL 5 printer provides the ability to print vector graphics using the HP-GL/2 graphics language. HP-GL/2 graphics may be created within application software, or imported from existing applications. For various types of images (many technical drawings and business graphics, for example), it is advantageous to use vector graphics instead of raster graphics. The advantages include faster I/O transfer of large images and smaller disk storage requirements. Note As a guideline, use raster graphics for small, complex images, or those images that cannot be accomplished with HP-GL/2 (such as scanned photographs). Use HP-GL/2 for images that would involve a large amount of I/O data transfer if printed using raster graphics, or for drawings that are already in HP-GL/2 format. If the image is easier to describe using vectors instead of raster lines, the image usually prints faster using HP-GL/2. Printing with HP-GL/2 requires leaving the PCL printer language mode and entering HP-GL/2 mode. Switching between modes involves only a few commands, and software applications easily switch between the two modes as needed. EN 17-1 Learning HP-GL/2 Read through this chapter and Chapter 18 for a general overview of the HP-GL/2 language and its relationship to the PCL printer language. Then, flip through the other HP-GL/2 chapters until you see an example that interests you or fits your objective. Read through the examples and try printing them using your choice of programming languages. If you need help converting the generic commands shown in the examples to a programming language, see "Using HP-GL/2 with Programming Languages" later in this chapter. As you see unfamiliar commands, find the page number of the command description in the index and read about the command. Think of an application that you would like to program and then look for an example that uses some of the elements you desire. After trying some examples and seeing how the commands interact, you should be well on your way to learning the HP-GL/2 language. This chapter describes the interaction between the PCL printer language and HP-GL/2 modes and introduces the following topics: HP-GL/2 Commands and Syntax Using HP-GL/2 with Programming Languages The HP-GL/2 Coordinate System HP-GL/2 and PCL Orientation Interactions The Vector Graphics Limits Units of Measure Pen Status and Location Defining the Image Area (PCL Picture Frame) Scaling Automatically Adjusting Image Size Absolute and Relative Pen Movement Chapter 18 covers more HP-GL/2 fundamentals, and Chapters 19 through 23 discuss HP-GL/2 commands and their syntax. 17-2 An Introduction to HP-GL/2 Vector Graphics EN HP-GL/2 Commands and Syntax There are two classes of commands used to print vector graphics: PCL printer language commands and HP-GL/2 commands. As the name implies, the PCL printer language commands are used when in the PCL printer language mode. They define the area on the page where HP-GL/2 graphics are printed and provide a means to enter HP-GL/2 mode. The HP-GL/2 commands are used within HP-GL/2 mode. They define the image that is printed, and allow you to return to the PCL printer language mode. The HP-GL/2 language has its own syntax, and each command is listed in this section of the manual. The vector graphics commands have been grouped into functional categories. The categories are designated as shown in Table 17-1 through . Each of the command categories is discussed in its own chapter, beginning with Chapter 19, The Configuration and Status Group. Table 17-1 The HP-GL/2 Commands by Group (1 of 5) CONFIGURATION GROUP CO DF IN IP IR IW PG1 RO RP1 SC Comment Default Values Initialize Input P1 and P2 Input Relative P1 and P2 Input Window Advance Page Rotate Coordinate System Replot Scale 1. Ignored by HP LaserJet printers. EN HP-GL/2 Commands and Syntax 17-3 Table 17-2 The HP-GL/2 Commands by Group (2 of 5) VECTOR GROUP AA AR AT BR BZ CI PA PD PE PR PU RT Arc Absolute Arc Relative Absolute Arc Three Point Bezier Relative Bezier Absolute Circle Plot Absolute Pen Down Polyline Encoded Plot Relative Pen Up Relative Arc Three Point Table 17-3 The HP-GL/2 Commands by Group (3 of 5) POLYGON GROUP EA EP ER EW FP PM RA RR WG Edge Rectangle Absolute Edge Polygon Edge Rectangle Relative Edge Wedge Fill Polygon Polygon Mode Fill Rectangle Absolute Fill Rectangle Relative Fill Wedge 17-4 An Introduction to HP-GL/2 Vector Graphics EN Table 17-4 The HP-GL/2 Commands by Group (4 of 5) CHARACTER GROUP AD CF CP DI DR DT DV ES FI1 FN1 LB LO SA SB SD SI SL SR SS TD Alternate Font Definition Character Fill Mode Character Plot Absolute Direction Relative Direction Define Label Terminator Define Variable Text Path Extra Space Select Primary Font Select Secondary Font Label Label Origin Select Alternate Font Scalable or Bitmap Fonts Standard Font Definition Absolute Character Size Character Slant Relative Character Size Select Standard font Transparent Data 1. These commands are part of HP-GL/2's Dual Context Extensions. EN HP-GL/2 Commands and Syntax 17-5 Table 17-5 The HP-GL/2 Commands by Group (5 of 5) LINE AND FILL ATTRIBUTES GROUP AC FT LA LT PW RF SM SP SV1 TR1 UL WU Anchor Corner Fill Type Line Attributes Line Type Pen Width Raster Fill Definition Symbol Mode Select Pen Screened Vectors Transparency Mode User-defined Line Type Pen Width Unit Selection 1. These commands are part of the Palette Extensions to HP-GL/2. As shown in the tables above, each HP-GL/2 command is a two-letter mnemonic code designed to remind you of its function. For example, IN is the Initialize command, SP is the Select Pen command, and CI is the Circle command. Parameters are used with certain HP-GL/2 commands to tell the printer to complete the command in a particular way. Understanding HP-GL/2 Syntax HP-GL/2 commands have four components: a mnemonic, parameter(s), separator(s), and a terminator. Refer to the following illustration of a typical HP-GL/2 command and the description of its components. 17-6 An Introduction to HP-GL/2 Vector Graphics EN Figure 17-1 Typical HP-GL/2 Command Mnemonic--The two-letter mnemonic reminds you of the command's function. The mnemonic can be uppercase or lowercase. Parameter(s)--Some commands have no parameters; for those commands which have them, parameters can be either required or optional (as indicated in the description of that command). Separator(s)--When you use parameters, you must separate them with a comma or space, or in the case of a numeric parameter, with a + or - sign. (Commas are recommended because some computers eliminate spaces, especially when sending variables.) Terminator--All commands require a terminator. Most HP-GL/2 commands are terminated by a semicolon or the first letter of the next mnemonic, a white space, or a tab (exceptions: LB uses a user-defined terminator; PE cannot use the first letter of the next mnemonic). The last command prior to exiting HP-GL/2 mode must be terminated with a semicolon. The following illustration shows the flexibility of the syntax. Each variation of the two-command sequence is permissible; however, the method shown on the left is recommended in most instances. The recommended method uses the first letter of the next mnemonic to terminate commands, uses no space between the mnemonic and its parameters, and separates parameters with a comma. (For clarity, examples in this HP-GL/2 section of the manual use semicolons as terminators, as shown in the middle example below.) Figure 17-2 Illustration of Syntax Flexibility EN HP-GL/2 Commands and Syntax 17-7 The next section explains how the syntax of individual commands is presented. Notations Used to Express Syntax The following describes the notations used in the syntax section of each command description: Mnemonic For readability, the mnemonic is shown in uppercase and separated from the parameters and/or terminator. parameters Parameters are shown in italic. [] Parameters in square brackets are optional. [param1,param2...[,param1,param2]] These optional parameters must be paired. params...params These parameters may be given the number of times specified in the command description. text...text This parameter indicates that you can type in a range of ASCII characters, such as in the Label (LB) command. (....) Indicates that you can use a range of the previous parameter; however, all X coordinates must have a corresponding Y coordinate. 17-8 An Introduction to HP-GL/2 Vector Graphics EN Note Remember that while X,Y coordinates are shown in parentheses in text [for example (3,4) or (0,0)], the parentheses are not part of the syntax. Do not enter these parentheses in your commands. ; iCommand terminator. In most HP-GL/2 commands, a semicolon is optional, and is shown in parentheses in most command syntax. Notes Three exceptions to the optional use of the semicolon as a command terminator occur in the following commands: Polyline Encoded (PE), Label (LB), and Comment (CO). PE must be terminated by a semicolon. LB is terminated by the nonprinting end-of-text character (ETX - decimal 3), or a user-defined character. The comment string of the CO command must be delimited by double quotes. A semicolon terminator is always required following the last command prior to leaving HP-GL/2 mode. , A comma is always shown as the separator between parameters. A space, +, or - is also valid (although not preferred). (A + or - is a valid separator only for numeric parameters.) Omitting Optional Parameters Some commands have optional parameters that take on default values if they are omitted. When you omit a parameter, you must omit all subsequent parameters in the same command (the Define Label Terminator (DT) command is an exception). For example, the Line Type (LT) command has three optional parameters: type, pattern length, and mode. The following command shows all three being used (type = 6, pattern length = 25, mode = 1). LT6,25,1 EN HP-GL/2 Commands and Syntax 17-9 If you omit the second parameter you must also omit the third parameter, as shown below: LT6 The printer uses the most recently specified pattern length and mode. If you have not specified a length or mode since sending a Default Values (DF) or Initialize (IN) command, the printer uses the parameter's defaults. For example, if you send the following command (omitting the second parameter), the printer interprets the "1" as the second parameter: LT6,1 Parameter Formats You must give parameters in the format (type of units) required by each HP-GL/2 command. The required format is stated in the parameter table of each command's description, and is described as follows. 1 Integer--An integer from ­1,073,741,823 (­230 +1) to 1,073,741,823 (230 ­ 1). The printer automatically rounds fractional parameters to the nearest integer within the range. Sending a number outside the parameter range may produce unexpected results. Clamped Integer--An integer from ­32,768 (­215) to 32,767 (215 ­1). The printer automatically rounds fractional parameters to the nearest integer. Sending a number outside this range does not cause an error, but the number is "clamped" to the limits of the range. For example, when parsing a clamped integer, the printer treats all numbers above 32,767 as 32,767. 2 Certain commands have parameters which are restricted to a smaller range. These ranges are listed in the parameter tables for each command. Sending a number outside the reduced parameter range may produce unexpected results. 3 Real--A number with an integer portion from ­1,073,741,823 (­230 +1) to 1,073,741,823 (230 ­ 1). You are assured of at least 6 significant digits (including integer and fractional portion). You may omit the decimal point when no decimal fraction is specified. Sending a number outside the parameter range may produce unexpected results. EN 17-10 An Introduction to HP-GL/2 Vector Graphics 4 Clamped Real--A number with an integer portion from ­32,768 to 32,767; you are assured of at least 6 significant digits (including integer and fractional portion). You may omit the decimal point when no decimal fraction is specified. Sending a number outside this range does not cause an error, but the number is "clamped" to the limits of the range. For example, the printer treats all numbers above 32,767 as 32,767. Certain commands have parameters which are restricted to a smaller range. These ranges are listed in the parameter tables for each command. Sending a number outside the reduced parameter range may produce unexpected results. 5 Label--Any sequence of characters. In the HP-GL/2 language, text is described using the term "label." Refer to the Label (LB) command in Chapter 23 for a complete description. Note Numbers within the above-mentioned ranges do not cause errors; however, the range may exceed the printer's physical printing area. Numbers that move the pen position outsi ...