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<h1>Surface Evolver Newsletter no. 20</h1>
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Surface Evolver Newsletter 20
January 1, 2008
by Ken Brakke, firstname.lastname@example.org
Surface Evolver version 2.30 available for download at
This is the first release since version 2.26 in August, 2005.
For those who compile Evolver themselves, the same makefile may be used.
New features in version 2.30:
The graphics display now has user-controlled clipping planes, so you
can see inside your surface. In the OpenGL graphics window, if you
hit the 'l' key (lower case 'L'), a clipping plane will appear. Dragging
the mouse will translate the clipping plane, and hitting 'k' will let you
rotate the clipping plane. See "clip view" in the documentation for more.
There is also a slice view mode, that works like clip view, except it
produces a two-dimensional cross-section of the surface. To initiate it,
use the "slice_view" toggle command; thereafter the 'l' and 'k' keys
control the mouse mode.
For scrolling through stages of an evolution in full 3D fashion, I have
written a program "evmovie" that reads simple geometry files and makes
an Evolver-like display, so you can manipulate the surface with the mouse
(with clipping plane!) and scroll through the files. It can handle
hundreds or even thousands of files pretty smoothly. There is a new
Evolver command "binary_off_file" for producing files for evmovie.
To download and see documentation, go to
Loading multiple surfaces:
The "addload" command will load a new datefile without deleting the
current surface. Good for building up a surface from several component
parts, particularly if one componont is repeated in multiple places.
See the addload_example.fe datafile in the distribution for an example.
You can display simple text in graphics (OpenGL and PostScript graphics,
text_id := display_text(x,y,string)
The x,y coordinates of the start of the string are in window units, i.e.
the window coordinates run from (0,0) in the lower left to (1,1) in the
upper right. The return value should be saved in a variable in case you want
to delete the text later with delete_text(text_id); even if you don't want to
delete it, you must have something on the left of the assignment for syntax
purposes. No font size control or font type or color implemented. Meant for
captioning images, for example a timer in frames of a movie.
Showing string facets:
In the string model, facets will now be displayed according to the
"show facet where expr" command. Facets can be colored and picked.
If the facet edge loop is not closed, then a closing edge will be
assumed. May not work too well for non-convex facets.
Several basic operations that work on whole arrays have been added
to the Evolver command language, so scripts can avoid tedious "for"
array := array
array := scalar
array := scalar * array
array := array + array
array := array - array
vector dot_product vector
These work on element attributes that are vectors or arrays, as well
as stand-alone arrays. I decided to use "dot_product" as the name of
the inner product operator instead of just "dot" since I had several
scripts using "dot" as a variable, and I assume other people do also,
and I didn't want to break those. There are also matrix_inverse() and
NOTE: the matrix_inverse() function is now a function returning 0 for
singular and 1 for nonsingular matrix, rather than a procedure not
returning a value. This means that scripts using matrix_inverse() will
have to assign the return value to a variable.
Element array attributes:
For use with the whole-array commands, these element attributes
are defined as 1-dimensional arrays:
vertices: __x (coordinates), __p (boundary parameters), __vertex_normal
The syntax for declaring identifiers to have local scope has been extended
to permit multiple names in the same declaration, such as
Deeper recursive calls:
The stack mechanism of the expression interpreter has been modified
to permit much deeper recursion, for example in geometric search
Several features have been added to help in debugging scripts:
"subcommand" command: Displays a command prompt and accepts user
commands. At "exit", it resumes the script.
"abort" ends all script execution and returns to the main
"breakpoint" can be used to cause a command prompt to appear when
execution reaches a certain line in a script. The syntax is
breakpoint scriptname linenumber
where scriptname is hte name of the procedure or function and
linenumber is the line number in the file the procedure is defined in.
There is also an "unset breakpoint" commmand.
"whereami" at a subcommand or breakpoint prompt will print a stack
trace so you can tell where you are in your scripts.
On systems where Evolver has cpu_counter available and Evolver has been
compiled with the manifest constant PROF_EVALS defined, the expression
evaluator inside Evolver keeps track of the clock cycles elapsed during
each expression evaluation. These expressions include procedures,
functions, constraint and boundary formulas, content integrands, energy
integrands, quantity integrands, etc; everything that prints out as code in
a dump file. The "print profiling" command will print the accumulated CPU
cycles so far for each type of expression. The times are inclusive of any
child functions or procedures. The command reset_profiling will set all
the cycle values back to 0.
New named methods:
dirichlet_elastic: to do conformal mapping by minimizing Dirichlet energy.
laplacian_mean_curvature: to do motion by the laplacian of the
function_quantity_sparse: uses sparse matrices with function-type quantities.
If your datafile or script generates harmless warnings, you can suppress
particular warnings by number. Syntax:
To help in scripts that want to iterate over constraints or boundaries,
there are read-only variables high_constraint and high_boundary for the
maximum constraint and boundary numbers (remember that for named
constraints and boundaries, the names are synonyms for numbers),
and there are boolean functions valid_constraint() and valid_boundary()
that take numbers or names as arguments.
Autopop and autochop improvements:
Autopop in the soapfilm model now deletes small facets.
The immediate_autopop toggle causes deletion of short edges or facets
to be done immediately on detection before proceeding with detetecting
further small edges or facets.
The read-write internal variahle autochop_length can be used to read or
set the autochop critical length without changing the autochop toggle
Edge deletion options:
Toggle force_deletion will force edge or facet deletion to happen
even if it creates two edges with the same endpoints.
Togglw star_fcnagling will refine edges that would otherwise wind
up with same endpoints due to an edge or facet deleteon.
End of Newsletter 20