The primitive routines can be used in any combination and order after the viewport and window have been defined. They all indicate where the primitive is to appear on the view surface by specifying world coordinates. See the subroutine descriptions in Appendix A for more details.
PGLINE.
This draws
one or more connected straight-line segments (generally called a
polyline in computer graphics). It has three arguments: the
number (N) of points defining the polyline, and two
arrays (XPTS and YPTS) containing the world
x and y-coordinates of the points. The polyline
consists of N-1 straight-line segments connecting points 1--2, 2--3, ...,
(N-1)--N:
CALL PGLINE (N, XPTS, YPTS)
The two routines PGMOVE and PGDRAW are even more
primitive than PGLINE, in the sense that any line graph
can be produced by calling these two routines alone. In general,
PGLINE should be preferred, as it is more
modular. PGMOVE and PGDRAW are provided for
those who are used to Calcomp-style plotting packages.
PGMOVE moves the plotter ``pen'' to a specified point,
without drawing a line (``pen up''). It has two arguments: the
world-coordinates of the required new pen position.
PGDRAW moves the plotter ``pen'' from its current
position (defined by the last call of PGMOVE or
PGDRAW) to a new point, drawing a straight line as it
goes (``pen down''). The above call to PGLINE could be
replaced by the following:
CALL PGMOVE (XPTS(1), YPTS(1))
DO I=2,N
CALL PGDRAW (XPTS(I), YPTS(I))
END DO
PGPT draws one or
more graph markers (sometimes called a polymarker). It has
four arguments: the number (N) of points to mark, two
arrays (XPTS and YPTS) containing the world
x and y-coordinates of the points, and a number
(NSYM) identifying the symbol to use:
CALL PGPT (N, XPTS, YPTS, NSYM)
The symbol number can be: -1, to draw a dot of the smallest possible
size (one pixel); 0--31, to draw any one of the symbols in Figure 4.1;
-3 - -8, to draw regular polygon with 3--8 sides; 33--127, to draw the
corresponding ASCII character (the character is taken from the
currently selected text font); or >127, to draw one of the Hershey
symbols from Appendix B. The Fortran
ICHAR function can be used to obtain the ASCII value;
e.g., to use letter F :
CALL PGPT (1, 0.5, 0.75, ICHAR('F') )
PGTEXT, which writes a
horizontal character string starting at a specific (x,y) world
coordinate position, e.g.,
CALL PGTEXT (X, Y, 'A text string')
PGTEXT is actually a simplified interface to the more
general primitive routine PGPTXT, which allows one to
change orientation and justification of the text, e.g.,
CALL PGPTXT (X, Y, 45.0, 0.5, 'A text string')
writes the text at an angle of 45 degrees to the horizontal, centered
at (x,y).
Both PGTEXT and PGPTXT require the position
of the text string to be specified in world coordinates. When
annotating a graph, it is usually more convenient to position the text
relative to the edge of the viewport, rather than in world-coordinate
space. The routine PGMTXT is provided for this,
and PGLAB provides a
simple interface to PGMTXT for the normal job of
annotating an (x,y) graph.
The appearance of text can be altered by specifying a number of attributes, described in the next chapter. In particular, the character size and character font can be changed. Figure 4.2 illustrates some of the possibilities.
To include one of the graph marker symbols (0--32) in a text string, use the
Fortran CHAR function, e.g.,
CALL PGTEXT (X, Y, 'Points marked with '//CHAR(17))
PGPTXT (and all the PGPLOT routines which
call it, e.g., PGTEXT, PGLAB) allows one to
include escape sequences in the text string to be
plotted. These are character-sequences that are not plotted, but are
interpreted as instructions to change font, draw superscripts or
subscripts, draw non-ASCII characters (e.g., Greek letters), etc. All
escape sequences start with a backslash character
(\). The following escape sequences are defined (the
letter following the \ may be either upper or lower
case):
| \u | start a superscript, or end a subscript |
| \d | start a subscript, or end a superscript (note that \u and \d must always be used in pairs) |
| \b | backspace (i.e., do not advance text pointer after plotting the previous character) |
| \fn | switch to Normal font (1) |
| \fr | switch to Roman font (2) |
| \fi | switch to Italic font (3) |
| \fs | switch to Script font (4) |
| \\ | backslash character (\) |
| \x | multiplication sign (×) |
| \. | centered dot (·) |
| \A | ångström symbol (Å) |
| \gx | greek letter corresponding to roman letter x, as indicated in Figure 4.3 |
| \mn \mnn |
graph marker number n or nn (1-31), as indicated in Figure 4.1 |
| \(nnnn) | character number nnnn (1 to 4 decimal digits) from the Hershey character set; the closing parenthesis may be omitted if the next character is neither a digit nor ``)''. This makes a number of special characters (e.g., mathematical, musical, astronomical, and cartographical symbols) available. See Appendix B for a list of available characters. |
The routine PGPOLY
is used to fill an area defined as a polygon. It has three arguments:
the number (N) of vertices defining the polygon, and two
arrays (XPTS and YPTS) containing the world
x and y-coordinates of the vertices:
CALL PGPOLY (N, XPTS, YPTS)
If the polygon is not convex, it may not be obvious which points in the
image are inside the polygon. PGPLOT assumes that a point is inside the
polygon if a straight line drawn from the point to infinity intersects
an odd number of the polygon's edges.
For the special case of a rectangle with edges parallel to the
coordinate axes, it is better to use routine PGRECT instead of
PGPOLY; this routine will use the hardware rectangle-fill
capability if available. PGRECT has four arguments: the
(x,y) world coordinates of two opposite corners (note the order
of the arguments):
CALL PGRECT (X1, X2, Y1, Y2)
To draw a circle use routine PGIRC. This routine has
three arguments: the (x,y), world coordinates of the center,
and the radius in world coordinates. Note that a circle may appear
elliptical if the world-coordinate scaling is not the same in x
and y.
CALL PGCIRC (X, Y, RADIUS)