Node:Drawing Points Intro, Next:Labeling Points Intro, Previous:Drawing and Labeling Points, Up:Drawing and Labeling Points
It's all very well to declare Points
, place them at particular
locations, print their locations to standard output, and transform them,
but none of these operations produce any MetaPost output.
In order to do this, the first step is to use drawing and
filling commands. The drawing and filling commands in 3DLDF are
modelled on those in Metafont.
The following example demonstrates how to draw a dot specifying a
Color
(see Color Reference) and a
pen1.
Point P(0, 1); P.drawdot(Colors::black, "pencircle scaled 3mm");
Fig. 3.
In drawdot()
, a Color
argument precedes the
string
argument for the pen, so "Colors::black
" must be
specified as a placeholder in the call to
drawdot()
.2
The following example "undraws" a dot at the same location using a
smaller pen. undraw()
does not take a Color
argument.
p.undrawdot("pencircle scaled 2mm");
Fig. 4.
For complete descriptions of drawdot()
and undrawdot()
,
see Point Reference; Drawing.
Drawing and undrawing dots is not very exciting. In order to make a
proper drawing it is necessary to connect the Points
. The most
basic way of doing this is to use the Point
member function
draw()
with a Point
argument:
Point p0; Point p1(2, 2); p0.draw(p1);
Fig. 5.
p0.draw(p1)
is equivalent in its effect to
p1.draw(p0)
.
The function Point::draw()
takes a required Point&
argument (a reference3
to a Point
) an optional Color
argument, and optional string
arguments for
the dash pattern and the
pen. The string
arguments, if present, are passed unchanged to
the output file.
The empty string
following the
argument p1
is a placeholder for the dash pattern argument, which
isn't used here.
p0.draw(p1, Colors::gray, "", "pensquare scaled .5cm rotated 45");
Fig. 6.
The function Point::undraw()
takes a required Point&
argument and
optional string
arguments for the dash pattern and the
pen. Unlike Point::draw()
, a Color
argument would have no
meaning for Point::undraw()
.
The string
arguments are passed unchanged to the output file.
undraw()
can be used to "hollow out" the region
drawn in [the previous figure]
. Since a dash pattern is used, portions
of the middle of the region are not undrawn.
p0.undraw(p1, "evenly scaled 6", "pencircle scaled .2cm");
Fig. 7.
For complete descriptions of draw()
and undraw()
,
see Point Reference; Drawing.
Pens are a concept from Metafont. In 3DLDF,
there is currently no type ``Pen
''. Pen arguments to functions
are simply strings
, and are written unaltered to out_stream
.
For more information about
Metafont's pens
, see
Knuth, The Metafontbook, Chapter 4.
Colors
are declared in the
namespace Colors
, so if you have
a ``using
'' declaration in the function where you use
drawdot()
, you can write ``black
'' instead of
``Colors::black
''. For more information about namespaces, see
Stroustrup, The C++
Programming Language, Chapter 8.
``A reference is an alternative name for an object. The main use of references is for specifying arguments and return values for functions in general and for overloaded operators (Chapter 11) in particular.'' Stroustrup, The C++ Programming Language, section 5.5, p. 97.