fungraph.scm library provides the procedures for
producing graphical images described in Concrete Abstractions.
Because these procedures operate like mathematical functions, we refer
to them as functional graphics, hence the name fungraph.
(line -1 -1 1 1) to see a diagonal line appear
on your screen. Instead, you have to explicitly apply the draw procedure
to the image, as in (draw (line -1 -1 1 1)). Note that this wrapping of
draw around images should only be done for top-level evaluations typed
in by the user, not internally to procedures that operate on images.
For example, in Chapter 1's application section, you might do
(draw (pinwheel rcross-bb)) to see what a pinwheeled rcross-bb looks like,
but you wouldn't use draw anywhere in pinwheel. Pinwheel still constructs
an image just as in the book; the only difference is that you now need to
make that resulting image appear on the screen by using draw.
In addition to the procedures described in the textbook, there are three additional ones:
(draw image)
(mirror-image image)
quarter-turn-right or invert, this
takes an image and makes another, related image. In the case of
mirror-image, the new image is the same size as the
original, and is formed by flipping the original image around a
vertical axis, as though it were viewed in a mirror.
(resize-image image width height)
(resize-image image size)
(resize-image image size size),
i.e., the specified size is used as both the width and the height
of the new image.
(resize-image image)
(resize-image image default-image-size default-image-size),
i.e., the width and height are both taken as the value of
default-image-size. As described below, this is the same
name that controls the size of the images created by
line and
filled-triangle.
The images produced by line and
filled-triangle are of a size determined by the value of
the name default-image-size. Initially this name is
defined as 60. This is a compromise size, rather small for the
fractals in chapter 4 and a bit large for each basic block of the
quilts in chapters 1-3. You can redefine it to another value (which
must be an exact, positive integer) to suit your own needs. Or, you
can use the resize-image procedure described above.
Or, as a final option, you can specify a size as an additional
argument to the basic image construction procedures, as in the
following example:
(filled-triangle 0 1 0 -1 1 -1 25)You can specify a size in this way with
line
as well as filled-triangle, and can
also specify two values, for width and height, as with
resize-image.
The overlay and stack procedures are not
restricted to two arguments, but rather can take one or more.