amino  1.0-beta2
Lightweight Robot Utility Library
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Scene Graph Compiler

The scene graph compiler aarxc parses scene files and outputs C code, which you can compile and link either statically into your application or into a shared library.

Why compile scenes?

  • Fast: Compiled scene are fast to load (<1ms) because the operating system directly maps into memory (via mmap) the included mesh data, eliminating runtime parsing and processing.
  • Memory-Efficient: Compiled scenes reduce memory use compared to runtime parsing when multiple processes operate on the same scene, because the memory mapped scene graphs in different processes share physical memory.
  • Convenient: Compiled scenes are easy to distribute to other machines – e.g., a cluster – which may lack scene sources, utilities, or support libraries. Only the executable or shared library is required to load the compiled scene, reducing potential runtime dependencies.
  • Real-Time: Compiled scenes avoid the need to include large parsing libraries – e.g., an XML parser – in real-time processes and reduce the dynamic allocations necessary to load the scene.
  • Composable: Multiple compiled scenes can be efficiently composed at runtime. Thus, the static scene graph for the robot could be compiled ahead of time for fast loading and then extended at runtime with the environment data either procedurally or by separately compiling the environment scene.

Compiled scenes do, however, present an initial, one-time compilation cost, around 10-20 seconds for common robot models. The following table summarizes average compilation time (10 runs) – including mesh processing, code generation, and C compilation – using Blender 2.77 and GCC 4.9.2 on an Intel(R) Core(TM) i7-4790:

Robot Compilation Time Run-Time Loading
Rethink Baxter 14.0s 0.33ms
Universal UR10 11.7s 0.17ms
Kinova Jaco 15.6s 0.20ms

Compiling Scene Files

The following command will convert the Example Scene into the C file table.c:

aarxc table.robray -n table -o table.c

To simply view a scene file, use the --gui option:

aarxc --gui table.robray

Note: Aarxc converts any meshes referenced in the source scene file to Wavefront OBJ using Blender and then directly parse the OBJ file. To load non-OBJ meshes (e.g., COLLADA/DAE), you must have Blender installed.

See also
Scene Files

Loading Scene Graphs

If your application needs to deal with only a particular scene graph, then you can link directly against the compiled C file.

If your application may need to deal with a variety of scene graphs, you can compile the C files for the scene graphs as shared objects and dynamically load them using aa_rx_dl_sg().

Static Linking

If you have a single scene graph and a single application, then it is sufficient to statically link the scene graph into your application, just as you would with any other C file. For example, to compile and link using GCC:

PKG_CONFIG_MODULES="amino amino-gl sdl2 glew"
CFLAGS="$CFLAGS `pkg-config --cflags $PKG_CONFIG_MODULES`"
LIBS="$LDLAGS `pkg-config --libs $PKG_CONFIG_MODULES`"
gcc $CFLAGS $LIBS table.c MY_OTHER_SOURCE_FILES -o MY_PROGRAM

(Of course, you would typically use a build automation tool such as Make, the Autotools, or CMake.)

Then, load the scene graph with the following C code:

struct aa_rx_sg *scenegraph = aa_rx_dl_sg__table(NULL);
See also
Autools pkg-config support via PKG_CHECK_MODULES
CMake's FindPkgConfig

Dynamic Linking

If multiple applications need to use the same scene graph, you will reduce disk and memory use by compiling the scene graph into a shared object. The details of building shared libraries vary by platform and are best managed with build automation tools such as the Autotools or CMake. For simple cases using gcc on GNU/Linux, you can build a shared library as follows:

PKG_CONFIG_MODULES="amino"
CFLAGS="$CFLAGS `pkg-config --cflags $PKG_CONFIG_MODULES`"
gcc -shared -fPIC $CFLAGS table.c -c -o libscene-table.so

The code to load the scene graph is identical to the static linking case.

See also
Shared Libraries with Automake
CMake's add_library

Dynamic Loading

For dynamic loading, the scene graph C file must be compiled into a shared object. Amino provides the convenience function aa_rx_dl_sg which will load the shared object (via dlopen) and call the contained function to load the scene graph.

To load the previous table example after compiling the C code to shared object "libscene-table.so":

struct aa_rx_sg *scenegraph = aa_rx_dl_sg( "scene-table",
"table",
NULL );
See also
Building plugins with Autotools

Compiling URDF

Set the ROS_PACKAGE_PATH environment variable to point at your ROS installation, and call aarxc. For example, to compile the URDF for the Baxter robot:

export ROS_PACKAGE_PATH=/opt/ros/indigo/share/
aarxc package://baxter_description/urdf/baxter.urdf -o baxter-model.c -n baxter

The scene compiler can also convert URDF to its human-readable scene file syntax:

aarxc package://baxter_description/urdf/baxter.urdf -s baxter.robray

Visualization

When given the --gui option, the scene compiler will launch the Viewer GUI.

aarxc --gui package://baxter_description/urdf/baxter.urdf

You can set joint positions using the --var and --val options. The --list-vars option will display the names of all configuration variables.

aarxc --list-vars package://baxter_description/urdf/baxter.urdf
aarxc --gui  package://baxter_description/urdf/baxter.urdf \
    --var=right_s1 --val=-.5 \
    --var=right_e1 --val=1

In addition to the Viewer GUI, you can also create raytraced images using POV-Ray:

aarxc package://baxter_description/urdf/baxter.urdf \
    -p scene.pov --render \
    --cam-eye="2 2 1.75" \
    --cam-look="0 0 .5"

Options Summary

See also
Man Page