These functions create a twodimensional projection of the objects on the
Picture and write MetaPost code to out_stream for
drawing it.
The arguments:
const Focus& f
 The
Focus used for projection, also known as the center of
projection, or the camera.
This argument is used in the first version only.
The second version, without a const Focus& f argument,
merely calls the first version and passes it the global variable
default_focus as its first argument, so default_focus is
effectively the default for f. Defining two versions in this way makes it
possible to call
output() with projection as its first (and possibly only)
argument. If instead, f were an optional argument with
default_focus as its default, this wouldn't have been possible. It
also wouldn't be possible to have f have a default in the first
version, and to retain the second version, because the compiler wouldn't
be able to resolve a call to output() with no arguments.
const unsigned short projection
 Default:
Projections::PERSP .
The type of projection. Valid values are const unsigned shorts
defined in namespace Projections
(see Namespace Projections):
PERSP for the perspective projection,
PARALLEL_X_Y for parallel projection onto the xy plane,
PARALLEL_X_Z for parallel projection onto the xz plane, and
PARALLEL_Z_Y for parallel projection onto the zy plane.
%% !! TO DO:
I plan to add isometric and axionometric projections soon.
real factor
 Default: 1.
Passed from
output() to
extract() and from there to project() . The
world_coordinates of the Points that are projected are
multiplied by factor, which enlarges or shrinks the projected
image without altering the Picture itself. factor
is probably most useful for parallel projections, where the Focus
f isn't used; with a perspective projection, the parameters of
the Focus can be used to influence the size of the projected
image.
const unsigned short sort_value
 Default:
Sorting::MAX_Z .
The value used should be one of the constants defined in
namespace Sorting , See Namespace Sorting, above.
If MAX_Z (the default) is used, the Shapes on the
Picture are sorted according to the maximum zvalue of the
projective_extremes of the Points belonging to the
Shape . If MIN_Z is used,
they are sorted according to the minimum zvalue, and
if MEAN_Z is used, they are sorted according to the mean of
the maximum and minimum zvalues. If NO_SORT is used, the
Shapes are output in the order in which they were put onto the
Picture .
The surface hiding algorithm
implemented in 3DLDF is quite primitive, and doesn't always work right.
For Shapes that intersect, it can't work right.
I plan to work on improving the surface hiding algorithm soon. This is
not a trivial problem. To solve it properly, each Shape on a
Picture must be tested for intersection with every other
Shape on the Picture . If two or more Shapes intersect,
they must be broken up into smaller objects until there are no more
intersections. I don't expect to have a proper solution soon, but I
expect that I will be able to make some improvements.
See Surface Hiding.
const bool do_warnings
 Default:
true . If true , output() issues warnings
to stderr (standard error output) if a Shape cannot be
output because it lies
outside the limits set by the following arguments. Sometimes, a user
may only want to project a portion of a Picture , in which case
such warnings would not be helpful. In this case, do_warnings
should be false .
const real min_x_proj
 Default: 40. The minimum xcoordinate of the projection of a
Shape such that the Shape can be output.
If projective_coordinates[0] of any Point on a
Shape is less than min_x_proj, the Shape will not be
projected at all.
const real max_x_proj
 Default: 40.
The maximum xcoordinate of the projection of a
Shape such that the Shape can be output.
If projective_coordinates[0] of any Point on a
Shape is greater than max_x_proj, the Shape will not be
projected at all.
const real min_y_proj
 Default: 40.
The minimum ycoordinate of the projection of a
Shape such that the Shape can be output.
If projective_coordinates[1] of any Point on a
Shape is less than min_y_proj, the Shape will not be
projected at all.
const real max_y_proj
 Default: 40.
The maximum ycoordinate of the projection of a
Shape such that the Shape can be output.
If projective_coordinates[1] of any Point on a
Shape is greater than max_y_proj, the Shape will not be
projected at all.
const real min_z_proj
 Default: 40.
The minimum zcoordinate of the projection of a
Shape such that the Shape can be output.
If projective_coordinates[2] of any Point on a
Shape is less than min_z_proj, the Shape will not be
projected at all.
const real max_z_proj
 Default: 40.
The maximum zcoordinate of the projection of a
Shape such that the Shape can be output.
If projective_coordinates[2] of any Point on a
Shape is greater than max_z_proj, the Shape will not be
projected at all.
