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Mesh Processing Library

Overview

This package contains C++ libraries and programs demonstrating mesh processing research published in ACM SIGGRAPH (1992–1998):

• surface reconstruction (from unorganized, unoriented points)
• mesh optimization
• subdivision surface fitting
• mesh simplification
• progressive meshes (level-of-detail representation)
• geomorphs (smooth transitions across LOD meshes)
• view-dependent mesh refinement
• smooth terrain LOD
• progressive simplicial complexes

The source code has been updated to modern C++ style and for cross-platform use.

Requirements / dependencies

The code can be compiled with Microsoft Visual Studio using the solution (*.sln) and project (*.vcxproj) files.

On Unix (Linux, Mac OS, and Cygwin), the code compiles using the clang and gcc compilers and GNU make.

Reading/writing of images and videos is enabled using several options. If available, image I/O can use libpng/libjpeg or Windows Imaging Component (WIC). Video I/O can use Windows Media Foundation (WMF). Across all platforms, if the command ffmpeg is present in the PATH, it is spawned in a piped subprocess for both image and video I/O.

On Mac OS X, it is necessary to install XQuartz for X11 support and ffmpeg for image/video I/O.

Code compilation

Build using Microsoft Visual Studio

Open the mesh_processing.sln file and build the solution (typically as a "ReleaseMD - x64" build). Executables are placed in bin, bin/debug, bin/Win32, or bin/Win32/debug, depending on the build configuration.

Build using GNU make

The CONFIG environment variable determines which make/Makefile_config_* definition file is loaded. On Windows, CONFIG can be chosen among {win, w32, cygwin, mingw, mingw32, clang}, defaulting to win if undefined. On Unix platforms (Linux and Mac OS), CONFIG=unix is the unique and default setting.

For example, to build using the Microsoft cl compiler (Debug, placing *.exe into directory bin/win):
make -j8

To build all programs (into either bin/unix or bin/win) and run all unit tests:
make -j test

To build on Unix, forcing the use of the gcc compiler (default is clang):
make CC=gcc -j

To build just the main library using the mingw gcc compiler on Windows:
make CONFIG=mingw -j libHh

To build the Filtermesh program (into bin/clang) using the clang compiler on Windows:
make CONFIG=clang -j Filtermesh

To build all programs (into bin/cygwin) and run all demos using the gcc compiler under Cygwin:
make CONFIG=cygwin -j demos

To clean up all files in all configurations:
make CONFIG=all -j deepclean

Note that additional options such as debug/release, 32-bit/64-bit, and compiler tool paths/parameters are set in the various make/Makefile_* files. These need to be adjusted depending on the versions and installation paths of the tools. For instance, the line "rel ?= 0" in make/Makefile_config_win specifies a debug (non-release) build, and "$(call prepend_PATH,...)" in make/Makefile_base_vc sets the compiler directory.

Publications and associated programs/demos

	Surface reconstruction from unorganized points. Hugues Hoppe, Tony DeRose, Tom Duchamp, John McDonald, Werner Stuetzle. ACM SIGGRAPH 1992 Proceedings, 71-78. Signed-distance field estimated from a set of unoriented noisy points. Programs: Recon Demos: create_recon_*.{sh,bat}, view_recon_*.{sh,bat}
	Mesh optimization. Hugues Hoppe, Tony DeRose, Tom Duchamp, John McDonald, Werner Stuetzle. ACM SIGGRAPH 1993 Proceedings, 19-26. Traversing the space of triangle meshes to optimize model fidelity and conciseness. Programs: Meshfit Demos: create_recon_*, view_recon_*, create_simplified_using_meshopt, view_simplified_using_meshopt
	Piecewise Smooth Surface Reconstruction. Hugues Hoppe, Tony DeRose, Tom Duchamp, Michael Halstead, Hubert Jin, John McDonald, Jean Schweitzer, Werner Stuetzle. ACM SIGGRAPH 1994 Proceedings, 295-302. Subdivision surfaces with sharp features, and their automatic creation by data fitting. Programs: Subdivfit Demos: create_recon_cactus, view_recon_cactus
	Progressive meshes. Hugues Hoppe. ACM SIGGRAPH 1996 Proceedings, 99-108. Efficient, lossless, continuous-resolution representation of surface triangulations. Programs: MeshSimplify, reverselines, Filterprog Demos: create_geomorphs, view_geomorphs
	Efficient implementation of progressive meshes. Hugues Hoppe. Computers & Graphics, 22(1), 1998, 27-36. Progressive mesh data structures compatible with GPU vertex buffers. Programs: FilterPM, G3dOGL Demos: create_pm_club, view_pm_club, determine_approximation_error
	View-dependent refinement of progressive meshes. Hugues Hoppe. ACM SIGGRAPH 1997 Proceedings, 189-198. Lossless multiresolution structure for incremental local refinement/coarsening. Programs: FilterPM, G3dOGL Demos: create_sr_office, view_sr_office
	Smooth view-dependent level-of-detail control and its application to terrain rendering. Hugues Hoppe. IEEE Visualization 1998 Conference, 35-42. Visually smooth adaptation of mesh refinement using cascaded temporal geomorphs. Programs: StitchPM, G3dOGL Demos: create_terrain_hierarchy, view_terrain_hierarchy, create_sr_terrain, view_sr_terrain, view_gcanyon_*
	Progressive simplicial complexes. Jovan Popovic, Hugues Hoppe. ACM SIGGRAPH 1997 Proceedings, 217-224. Progressive encoding of both topology and geometry. Programs: G3dOGL Demos: view_psc_drumset

Demos

After the code is compiled, the demos can be run as follows.

In Windows, create, view, and clean up all the results using the batch scripts:

demos/all_demos_create_results.bat
demos/all_demos_view_results.bat
all_demos_clean.bat

On Unix-based systems (e.g. Linux, Mac OS, Cygwin), either run the bash scripts:

demos/all_demos_create_results.sh
demos/all_demos_view_results.sh
demos/all_demos_clean.sh

or alternatively (and faster), invoke make to create all results in parallel and then view them sequentially:

make [CONFIG=config] -j demos

Note that pressing the Esc key closes any open program window.

Filter programs

All programs recognize the argument --help (or -?) to show their many options.

The programs Filterimage, Filtermesh, Filtervideo, FilterPM, and Filterframe are all designed to:

• read media from std::cin (or from files or procedures specified as initial arguments),
• perform operations specified by arguments, and
• write media to std::cout (unless -nooutput is specified).

For example, the Filterimage command

Filterimage demos/data/gaudipark.png -rotate 20 -cropleft 100 -cropright 100 \
  -filter lanczos6 -scaletox 100 -color 0 0 255 255 -boundary border -cropall -20 \
  -setalpha 255 -color 0 0 0 0 -drawrectangle 30% 30% -30% -30% -gdfill \
  -info -to jpg >gaudipark.new.jpg

• reads the specified image,
• rotates it 20 degrees counterclockwise (with the default reflection boundary rule),
• crops its left and right sides by 100 pixels,
• scales it uniformly to a horizontal resolution of 100 pixels using a 6×6 Lanczos filter,
• adds a 20-pixel blue border on all sides,
• adds an alpha channel and creates an undefined (alpha=0) rectangular region in the image center,
• fills this region using gradient-domain smoothing,
• outputs some statistics on pixel colors (to std::cerr), and
• writes the result to a file under a different encoding.

As another example, the FilterPM command

FilterPM demos/data/standingblob.pm -info -nfaces 1000 -outmesh | \
  Filtermesh -info -signeddistcontour 60 -genus | \
  G3dOGL -key DmDe

• reads a progressive mesh stream to construct a mesh with 1000 faces,
• reports statistics on the mesh geometry,
• remeshes the surface as the zero isocontour of its signed-distance function on a 60³ grid,
• reports the new mesh genus, and
• shows the result in an interactive viewer using the specified view parameters,
• simulating keypresses Dm to enable flat shading and De to make mesh edges visible.

The Filtermesh command

FilterPM demos/data/spheretext.pm -nf 2000 -outmesh | \
  Filtermesh -angle 35 -silsubdiv -silsubdiv -mark | \
  G3dOGL -key DmDeDbJ---- -st demos/data/spheretext.s3d

• reads a 2000-face mesh, marks all edges with dihedral angle greater than 35 degrees as sharp,
• applies two steps of adaptive subdivision near these sharp edges, and
• shows the result flat-shaded (Dm), with edges (De), without backface culling (Db), spinning (J) somewhat slowly (----),
• starting from the view parameters stored in the spheretext.s3d file.

The Filtervideo command

Filtervideo demos/data/palmtrees_small.mp4 -filter keys -scaleu 1.5 >palmtrees_small.scale1.5.mp4

• reads the video (entirely into memory),
• uniformly scales the two spatial dimensions by a factor 1.5 using the Keys bicubic filter, and
• saves the new video.

The command

Filtervideo demos/data/palmtrees_small.mp4 -info -trimbeg 4 -boundary clamped -trimend -20% | \
    -tscale 1.5 -framerate 150% -croprectangle 50% 50% 400 240 -gamma 1.5 -bitrate 10m | \
  VideoViewer demos/data/palmtrees_small.mp4 - -key =an

• reads the video (entirely into memory),
• reports statistics on the color channels,
• trims off 4 frames at the beginning,
• adds repeated copies of the last frames (with length 20% of the video),
• temporally scales the content by a factor of 1.5 and adjusts the framerate accordingly,
• spatially crops a centered rectangle with width 400 pixels and height 240 pixels,
• adjusts the color gamma,
• sets the output bitrate to 10 megabits/sec, and
• shows the result (- for std::cin) together with the original video in an interactive viewer,
• with keypress = to scale the window by 2, a to loop all (two) videos, and n to initially select the next video.

Surface reconstruction

Recon

This program reads a list of 3D (x, y, z) points assumed to be sampled near some unknown manifold surface, and reconstructs an approximating triangle mesh. For example,

Recon <demos/data/distcap.pts -samplingd 0.02 | \
  Filtermesh -genus -rmcomp 100 -fillholes 30 -triangulate -genus | tee distcap.recon.m | \
  G3dOGL -st demos/data/distcap.s3d -key DmDe

• reads the text file of points,
• reconstructs a triangle mesh assuming a max sample spacing (δ+ρ in paper) of 2% of the bounding volume,
• reports the genus of this initial mesh,
• removes all connected components with fewer than 100 triangle faces,
• fills and triangulates any hole bounded by 30 or fewer mesh edges,
• reports the genus of the modified mesh,
• saves it to a file, and
• displays it interactively starting from a specified viewpoint, with flat-shaded faces (Dm) and mesh edges (De).

To show the progression of the Marching Cubes algorithm,

Recon <demos/data/distcap.pts -samplingd 0.02 -what c | \
  Filtera3d -split 30 | G3dOGL -key DCDb -st demos/data/distcap_backside.s3d -terse

• selects the 'c' (cubes) output stream,
• forces a frame refresh every 30 polygon primitive, and
• shows the result without display-list caching (DC) and without backface culling (Db).

To show a similar streaming reconstruction of the surface mesh,

Recon <demos/data/distcap.pts -samplingd 0.02 -what m | Filtermesh -toa3d | \
  Filtera3d -split 30 | \
  G3dOGL demos/data/distcap.pts -key DCDb -st demos/data/distcap_backside.s3d -terse -input -key _Jo

• selects the default 'm' (mesh) output stream,
• converts the mesh to a stream of polygons, and
• shows the points and streamed reconstruction with a slow (_) rotation (J) about the object frame (o).

The same program can also read a list of 2D (y, z) points to reconstruct an approximating curve:

Recon <demos/data/curve1.pts -samplingd 0.06 -grid 30 | \
  Filtera3d -joinlines | tee curve1.a3d | \
  G3dOGL demos/data/curve1.pts -input -st demos/data/curve1.s3d

Meshfit

Given an initial mesh and a list of 3D points, this program optimizes both the mesh connectivity and geometry to improve the fit, i.e. minimizing the squared distances from the points to the surface. For example,

Meshfit -mfile distcap.recon.m -file demos/data/distcap.pts -crep 1e-5 -reconstruct | \
  tee distcap.opt.m | G3dOGL -st demos/data/distcap.s3d -key DmDe

• reads the previously reconstructed mesh and the original list of points,
• applies an optimized sequence of perturbations to improve both the mesh connectivity and geometry,
• using a specified tradeoff between mesh conciseness and fidelity (c_rep=1e-4 yields a coarser mesh),
• saves the result to a file, and displays it interactively.

The input points can also be sampled from an existing surface, e.g.:

Filtermesh demos/data/blob5.orig.m -randpts 10000 -vertexpts | \
  Meshfit -mfile demos/data/blob5.orig.m  -file - -crep 1e-6 -simplify | \
  G3dOGL -st demos/data/blob5.s3d -key DmDe

To view the real-time fitting optimization,

Meshfit -mfile distcap.recon.m -file demos/data/distcap.pts \
  -crep 1e-5 -outmesh - -record -reconstruct | \
  G3dOGL -st demos/data/distcap.s3d -key DmDeDC -async -terse

• writes both the initial mesh and the stream of mesh modifications, and
• displays the changing mesh asynchronously with display-list caching disabled (DC).

Polyfit

This related program performs a similar optimization of a 1D polyline (either open or closed) to fit a set of 2D points. For example,

Polyfit -pfile curve1.a3d -file demos/data/curve1.pts -crep 3e-4 -spring 1 -reconstruct | \
  G3dOGL demos/data/curve1.pts -input -st demos/data/curve1.s3d

• reads the previously reconstructed polyline and the original list of points,
• optimizes vertex positions and simplifies the number of line segments according to some representation cost, and
• displays the result together with the original points.

Subdivfit

In a subdivision surface representation, a coarse base mesh tagged with sharp edges defines a piecewise smooth surface as the limit of a subdivision process. Such a representation both improves geometric fidelity and leads to a more concise description.

Filtermesh distcap.opt.m -angle 52 -mark | \
  Subdivfit -mfile - -file demos/data/distcap.pts -crep 1e-5 -csharp .2e-5 -reconstruct >distcap.sub0.m

• reads the previously optimized mesh and tags all edges with dihedral angle greater than 52 degrees as sharp,
• loads this tagged mesh and the original list of points,
• optimizes the mesh connectivity, geometry, and assignment of sharp edges to fit a subdivision surface to the points,
• with a representation cost of 1e-5 per vertex and .2e-5 per sharp edge, and
• saves the resulting optimized base mesh to a file. (The overall process takes a few minutes.)

To view the result,

G3dOGL distcap.sub0.m "Subdivfit -mf distcap.sub0.m -nsub 2 -outn |" \
  -st demos/data/distcap.s3d -key NDmDe -hwdelay 5 -hwkey N

• reads the base mesh together with a second mesh obtained by applying two iterations of subdivision,
• shows the first mesh (N) with flat-shaded faces and edges (DmDe),
• waits for 5 seconds, and displays the second mesh (N) as a smooth surface without edges.

MeshDistance

This program computes measures of differences between two meshes. It samples a dense set of points from a first mesh and computes the projections of each point onto the closest point on a second mesh.

MeshDistance -mfile distcap.recon.m -mfile distcap.opt.m -bothdir 1 -maxerror 1 -distance

• MeshDistance loads the earlier results of mesh reconstruction and mesh optimization,
• computes correspondences from points sampled on each mesh to the other mesh (in both directions), and
• reports differences in geometric distance, color, and surface normals, using both L² (rms) and L^∞ (max) norms.

Mesh simplification

Given a mesh, MeshSimplify applies a sequence of edge collapse operations to simplify it to a coarse base mesh while trying to best preserve the appearance of the original model. It supports many different simplification criteria, as well as face properties, edges tagged as sharp, and vertex and corner attributes (n_x,n_y,n_z normals, r,g,b colors, and u,v texture coordinates).

For example,

MeshSimplify demos/data/club.orig.m -prog club.prog -simplify >club.base.m

• reads the original mesh and randomly samples points over its surface,
• progressively simplifies it by examining point residual distances, while recording changes to a *.prog file, and
• writes the resulting base mesh.

The next step is to reverse the sequence of stored edge collapses, i.e. forming a progressive sequence of vertex splits:

reverselines club.prog >club.rprog

We construct a concise progressive mesh by encoding the base mesh together with the sequence of vertex splits that exactly recover the original mesh:

Filterprog -fbase club.base.m -fprog club.rprog -pm_encode >club.pm

The complete process from the original mesh to the progressive mesh is implemented by the script call

demos/bin/meshtopm.{sh,bat} demos/data/club.orig.m >club.pm

Given a progressive mesh, we can interactively traverse its continuous levels of detail:

G3dOGL -pm_mode club.pm -st demos/data/club.s3d -lightambient .4

• by dragging the left vertical slider using the left or right mouse button, and
• toggling mesh edges using the De key sequence.

We can also define geomorphs between discrete levels of detail, e.g.

FilterPM club.pm -nfaces 2000 -geom_nfaces 3300 -geom_nfaces 5000 -geom_nfaces 8000 | \
  G3dOGL -st demos/data/club.s3d -key SPDeN -lightambient .5 -thickboundary 1 -video 101 - | \
  VideoViewer - -key m

• creates a geomorph between 2000 and 3300 faces, another between 3300 and 5000 faces, and one more,
• shows these in a viewer with the level-of-detail slider enabled (S),
• selects all three geomorph meshes (P), enables mesh edges (De), selects the first mesh (N),
• records a video of 101 frames while moving the LOD slider, and
• shows the resulting video with mirror looping enabled (m).

This example displays a progressive mesh after truncating all detail below 300 faces and above 10000 faces:

FilterPM demos/data/standingblob.pm -nf 300 -truncate_prior -nf 10000 -truncate_beyond | \
  G3dOGL -pm_mode - -st demos/data/standingblob.s3d

As an example of simplifying meshes with appearance attributes,

Filterimage demos/data/gaudipark.png -scaletox 200 -tomesh | \
  MeshSimplify - -nfaces 4000 -simplify | \
  G3dOGL -st demos/data/imageup.s3d -key De -lightambient 1 -lightsource 0

• forms a planar grid mesh whose 200×200 vertices have colors sampled from a downsampled image,
• simplifies the mesh to 4000 faces while minimizing color differences,
• shows the result with mesh edges (De) and only ambient lighting.

Selective view-dependent mesh refinement

Within demos/create_sr_office, the script call

meshtopm.{sh,bat} demos/data/office.nf80000.orig.m -vsgeom >office.sr.pm

creates a progressive mesh in which the simplified vertices are constrained to lie at their original positions (-vsgeom). This enables selective refinement, demonstrated by

G3dOGL -eyeob demos/data/unit_frustum.a3d -sr_mode office.sr.pm -st demos/data/office_srfig.s3d \
  -key ,DnDeDoDb -lightambient .4 -sr_screen_thresh .002 -frustum_frac 2

The mesh is adaptively refined within the view frustum, shown as the inset rectangle (key Do) or in the top view (key Dr). Drag the mouse buttons to rotate, pan, and dolly the object.

Terrain level-of-detail control

Within demos/create_sr_terrain.{sh,bat},

Filterimage demos/data/gcanyon_elev_crop.bw.png -tobw -elevation -step 6 -scalez 0.000194522 \
    -removekinks -tomesh | \
  Filtermesh -assign_normals >gcanyon_sq200.orig.m
demos/bin/meshtopm.{sh,bat} gcanyon_sq200.orig.m -vsgeom -terrain >gcanyon_sq200.pm

• converts an elevation image to a smoothed terrain grid mesh, and
• simplifies it to create a selectively refinable mesh.

Then, within demos/view_sr_terrain.sh,

(common="-eyeob demos/data/unit_frustum.a3d -sr_mode gcanyon_sq200.pm -st demos/data/gcanyon_fly_v98.s3d \
   -texturemap demos/data/gcanyon_color.1024.png -key DeDtDG -sr_screen_thresh .02292 -sr_gtime 64 \
   -lightambient .5"; \
 export G3D_REV_AUTO=1; \
 G3dOGL $common -geom 800x820+100+10 -key "&O" -key ,o----J | \
   G3dOGL $common -geom 800x820+920+10 -async -killeof -input -key Dg)

• opens two synchronized side-by-side windows of the same texture mapped terrain,
• in which the first windows shows the temporal pops resulting from instantaneous mesh operations,
• whereas the second window shows the smooth appearance provided by runtime geomorphs (Dg).

For large terrain meshes, we form a hierarchical progressive mesh by partitioning the terrain mesh into tiles, simplifying each tile independently to form a progressive mesh, stitching the progressive meshes together 2-by-2, and recursively simplifying and merging at coarser pyramid levels.

An example is presented in demos/create_terrain_hierarchy. It makes use of

StitchPM -rootname terrain.level0 -blockx 2 -blocky 2 -blocks 32 -stitch >terrain.level0.stitched.pm

to assemble each 2-by-2 set of progressive mesh tiles terrain.level0.x{0,1}.y{0,1}.pm at the finest level.

The script demos/view_gcanyon_interactive launches an interactive flythrough over a Grand Canyon terrain model, using a progressive mesh precomputed from an original 4096×2048 height field.

Alternatively, demos/view_gcanyon_frames shows a real-time flythrough using a pre-recorded flight path, whereby keystroke commands embedded within the input stream automatically change viewing modes.

Topology simplification

The program MinCycles removes topological noise from a mesh by iteratively pinching off the smallest nonseparating cycle of edges until a specified criterion (cycle length, number of cycle edges, number of cycles, or mesh genus) is reached.

For example, within demos/create_topologically_simplified.{sh,bat},

FilterPM demos/data/office.pm -nf 200000 -outmesh | \
  MinCycles - -fraccyclelength 1.2 -maxcyclelen 0.10 -closecycles | \
  G3dOGL -st demos/data/office.s3d -key DeDEJ---- -thickboundary 0 -lightambient .9

• extracts a mesh of 200000 faces from a progressive mesh,
• closes 46 topological handles to reduce the mesh genus from 50 to 4,
• where the final remaining handle would require a nonseparating cycle of length greater than 0.10.
• speeding up the process by identifying approximately shortest nonseparating cycles within a factor 1.2 of optimal, and
• shows the resulting closed edge cycles (tagged as sharp) in blue.

Geometry viewer

The G3dOGL program shows interactive rasterized renderings of 3D (and 2D) geometry, represented as

• streams of polygons/polylines/points (*.a3d format),
• triangle meshes including geomorphs (*.m),
• progressive meshes (*.pm),
• encoded selectively refinable meshes (*.srm),
• progressive simplicial complexes (*.psc), or
• simple *.ply files.

Please see the many examples presented earlier. The viewer can also read *.frame elements to position the viewer and the objects in world space. Elements of *.a3d, *.m, and *.frame streams can all be interleaved in a single input stream.

The viewer can take image snapshots (see demos/create_rendered_mechpart_image) and record videos (see demos/create_rendered_mechpart_video).

The mouse/keyboard UI controls include:

 Mouse movements:
 left mouse:          rotate
 middle mouse:        pan
 right mouse:         dolly
 shift-left:          pan
 shift-middle mouse:  roll
 shift-right mouse:   zoom
 (mouse movements are with respect to current object; see '0-9' below)

 Important key strokes:
 ? : print complete list of keys
 D?: print list of keys prefixed by 'D'
 De: toggle edges
 Ds: toggle shading of faces
 Db: toggle backface culling
 Dm: toggle Gouraud/flat shading
 DP: save current window as an image file
 DS: toggle show some sliders
 S : toggle show some other sliders
 j : jump to a default viewpoint
 J : automatically rotate object
 D/: edit viewpoint filename
 , : read the viewpoint
 . : save the viewpoint
 0-9: select object (0=eye_frame, 1=first object, 2=second object...)
 u : display/hide current object
 N : select next object
 P : select previous object
 -=: decrease/increase the magnitude of all movements
 f : toggle flying (usually with '0' eye selected)

To record a 6-second (360-frame) video of a rotating mesh and then view the resulting video:

G3dOGL demos/data/standingblob.orig.m -st demos/data/standingblob.s3d -key iioJ \
  -video 360 output_video.mp4
VideoViewer output_video.mp4

The related program G3dVec shows wireframe hidden-line-removed renderings of *.a3d streams and *.m meshes. It can write vector-based Postscript figures (see demos/view_hidden_line_removed).

In both programs, the keys ? and D? show a list of available keyboard commands.

Image/video viewer

The VideoViewer program enables interactive viewing and simple editing of both images and videos. Again, the key ? shows a list of available keyboard commands. Press pageup/pagedown to quickly browse through the videos and/or images in a directory. Audio is not currently supported.

File formats

Mesh (*.m)

See the documentation at the end of libHh/GMesh.h

A mesh is a set of vertices and faces. These in turn also define edges and corners. Arbitrary string tuples can be associated with vertices, faces, edges, and corners. Examples of string tuples: {normal=(.1 .2 .3) rgb=(1 1 1) matid=5 material="string"}. See the several demos/data/*.m files for examples of the mesh format. Note that the indices of vertices and faces start at 1 instead of 0; in hindsight that was a poor choice.

Geometry stream (*.a3d, *.pts)

See the documentation at the end of libHh/A3dStream.h

The stream contains polygons, polylines, points, and control codes (like end-of-frame, end-of-input, change-of-object). Unlike in a mesh, these primitives do not share vertices. The stream can be either text or binary.

Frame stream (*.frame, *.s3d)

See the documentation at the end of libHh/FrameIO.h

This text or binary format encodes a 4×3 affine transformation (plus an object id and a scalar field-of-view zoom). It is used to record default viewing configurations, and sequences of frames for flythroughs. It usually represents the linear transform from object space (or eye space) to world space. The stream can be either text or binary.