To Open and Initialize for Output

Syntax Example

For C programs^[4]:

fildes = gopen("〈dev〉/plt", OUTDEV, "CADplt", RESET_DEVICE);
 
fildes = gopen("spoolfile", OUTDEV, "CADplt", RESET_DEVICE | SPOOLED);

For FORTRAN 77 programs:

  fildes = gopen('〈dev〉/plt'//char(0), OUTDEV,
+ 'CADplt'//char(0), RESET_DEVICE)
 
  fildes = gopen('〈dev〉/plt'//char(0), OUTDEV,
+ 'CADplt'//char(0), RESET_DEVICE+SPOOLED)

For Pascal programs:

fildes := gopen('〈dev〉/plt', OUTDEV, 'CADplt', RESET_DEVICE);
fildes := gopen('spoolfile', OUTDEV, 'CADplt', RESET_DEVICE+SPOOLED);

Parameters for gopen

The gopen procedure has four parameters: path, kind, driver, mode.

path - This is the name of the special device file created by the mknod command as specified in the section "Special Device Files" such as 〈dev〉/plt.
kind - This indicates the I/O characteristics of the device. This parameter may only be OUTDEV.
driver - This is the character representation of the driver type. This must be CADplt.
mode - This is the mode control word which consists of several flag bits which are or ed together. Listed below are the flag bits and their device dependent actions:
- SPOOLED - Open the device for spooled operation.
- 0 (zero) - Open the device but do nothing else.
- INIT - Open and initialize the device in a device dependent manner. For this device driver the INIT mode will send the HP-GL command DF to the device. This DF command will not change the following characteristics of the plotter:
  P1 and P2
  pen speed, force and acceleration
  90 degree rotation or axis alignment
- RESET_DEVICE - Open and completely initialize the device. For this device driver the RESET_DEVICE mode will send the HP-GL command IN to the device. This command will reset the device's configuration including P1 and P2.
- THREE_D - Open the device for three-dimensional primitives.

Device Defaults

Color Table

The HP-GL default color table is the same as the Starbase default color table. To read the current color table values, use the inquire_color_table procedure. The official color table is stored in the device driver allowing different color tables to be used for different devices in the same program. The default color map has eight entries as shown in the following table.

Table 1-2 Default Color Map

Pen	Color	Red	Green	Blue
0	white (pen up)	0.0	0.0	0.0
1	black	1.0	1.0	1.0
2	red	1.0	0.0	0.0
3	yellow	1.0	1.0	0.0
4	green	0.0	1.0	0.0
5	cyan	0.0	1.0	1.0
6	blue	0.0	0.0	1.0
7	magenta	1.0	0.0	1.0

You can change the color table values with the define_color_table procedure.

Red, Green and Blue Values

Functions that pass red, green and blue values are supported. The pen most closely corresponding in value to the red, green and blue values is selected using the current color table entries. A "square root of sum of squares" algorithm is used to identify the pen.

Device Coordinates

The default number of millimeters per device coordinates is 0.025. If the gopen mode is not SPOOLED, the device driver will inquire the device and use the value returned.

Device Coordinate Origin

The device coordinate origin (0, 0) is device dependent. You should consult your device hardware manual to get the origin. In general, the origin is normally centered between the P1 and P2 extent so that there are an equal number of negative and positive device coordinates on each side of the origin. One known exception is the HP 7550 plotter which places the origin in the lower left corner of the paper.

Device ID

If the device is not in SPOOLED mode, then the device driver will send the HP-GL command OI and use the returned string as the device ID. If the device is spooled, the device ID will be CADplt.

Line Types

The following table shows the default line types that are available.

Table 1-3 Line Types

Index	Type
0	`SOLID`
1	`DASH`
2	`DOT`
3	`DASH_DOT`
4	`CENTER_DASH_DASH`
5	`LONG_DASH`
6	`CENTER_DASH`
7	`CENTER_DASH_DASH`

Number of Pens

The default number of pens is 8. The number of pens may be specified using the HPGL_SET_PEN_NUMBER gescape.

P1 and P2

The values for P1 and P2 are device dependent and will vary depending on the gopen mode that was used when accessing the device as below:

INIT or 0 mode
The values of P1 and P2 will be equal to the current values set for the device. The device driver will inquire these values and use them unmodified. When a device is opened in this mode, it is the your responsibility to insure that appropriate P1 and P2 values are currently established.
RESET_DEVICE mode
The HP-GL command IN will be sent to the plotter. This will cause the device to reset P1 and P2 to take advantage of the full size of the paper that is currently loaded. The device driver will then inquire these values and use them. This mode insures that the current values of P1 and P2 will match the paper size that is loaded.
SPOOLED mode
Since the device driver cannot inquire the P1 and P2 values from the device, the driver assumes the limits are as below:
P1 x: -23144, P1 y: -17048 P2 x: 23144, P2 y: 17048
which are the limits for HP 7596A 36-inch roll paper. The device driver will then put the HP-GL command SC in the spool file. This will cause the device to scale the assumed P1 and P2 values to the actual P1 and P2 values in effect when the spooled file is dumped to the device. The affect of the scaling command is to cause the entire drawing to be expanded or compressed so that it will fill the P1 and P2 extent that the device currently has. In order to turn off the scaling function, the Starbase procedure set_p1_p2 with METRIC units must be called.




	NOTE: Some devices will not guarantee isotropic scaling when you spool to them. Check your device hardware manual to see if the HP-GL command `SC` supports the fifth parameter for isotropic scaling. If it does not, then the P1, P2 aspect ratio must match the default P1, P2 ratio above, or the drawing will be distorted.

Timeouts

An initial timeout of 10 seconds is used when the procedure gopen is called. If the device is accessed correctly by the gopen call within the timeout, then the timeout is removed completely for all further action. Should the device be taken off line or fail after a successful gopen call, the device driver can "hang" for an indefinite period of time.

^[4]The actual path names of directories in angle brackets depend on the file system structure. See the Graphics Administration Guide for details.