Blender

Blender is Article description::a free and open-source 3D creation suite. It supports modeling, rigging, animation, simulation, rendering, compositing and motion tracking, video editing, and 2D animation.

USE flags
There are many additional features that can be enabled via USE flags, and some of them are explained a little more in-depth later on in this article.

Additional features
This section lists many of the optional features available in blender and gives a brief overview of their use for beginning users.

Audio device support
Support for Jack, OpenAL, or SDL audio can optionally be enabled through their respective USE flags.

Inside Blender, go to the Edit->Preferences->System tab and set the Audio Dev to the desired setting.

CUDA support
Cycles renderer can work on GPUs, for example Nvidia GTX 970 is about twice as fast as an i5 4690k on traditional BMW benchmark.

To enable graphics card rendering with Nvidia graphics cards, install Cuda:

Inside Blender, go to the Edit->Preferences->System tab and set Compute Device to CUDA and select the graphics card in the box below. If the graphics card is not supported these options will not be visible.

Now set the renderer to Cycles Renderer and in the renderer panel under the Render options set the Device to GPU Compute.

The first time a render is created with a new version of blender, the CUDA kernels will need to be compiled. This may take over 15 minutes.

File format support
Support OpenCOLLADA (.dae), jpeg2k, sndfile, and tiff image file formats can optionally be enabled through USE flags.

The  USE flag adds entries to File->Import/Export for Collada (Default) (.dae) files. The others can be used with background images in the properties panel of the 3D View or as output formats in the render panel.

Blender should work with either ffmpeg or libav libraries, although only ffmpeg is officially recommended by the Blender developers.

Headless (server only)
For render farms it is possible to compile blender with the  USE flag. This is not recommended for most users.

This feature reduces the Blender file size by around 5 MB, but it will not be possible to run blender normally as the GUI is not available.

In headless mode, Blender can still be used to run python scripts from the commmand line:

Memory allocator
It is recommended to enable  to use a more efficient memory allocator. This reduces wasted memory during rendering and allows for larger scenes to be rendered.

Memory profiling
Support for memory profiling can be enabled using the  USE flag. See Debugging for instructions on setting up Valgrind.

OpenColorio
Open Colorio provides additional options under the Color Management section of the Scene panel.

Inside Blender, select the Render View and Look options, and adjust the exposure, gamma, and curves to obtain the desired look.

Opensubdiv
Opensubdiv is a set of libraries that improve subdivision surface modifier evaluation. This can dramatically improve the frame rate of viewing animations in the viewport when using high levels of subdivision.

Not all cards are suitable. The current code checks for geometry shader, GL_ARB_gpu_shader5, glProgramParameteri, glProgramParameteriEXT, and glProgramParameteriARB. These are available as part of OpenGL 3.2, 4.0, and 4.1, or as extensions.

The only way to use a subdivision surface modifier is to enable the  USE flag.

OpenVDB
OpenVDB provides a data structure for storing and manipulating volumetric information efficiently. It can be compiled into blender using the  USE flag, and   is also recommended as the data can require upwards of 20MB.

In Blender, set the renderer to Cycles Renderer. Go to the physics panel and enable physics for Smoke. In the smoke section select Domain. Save the file to enable editing of the smoke cache. Change File Format to Openvdb and select Blosc compression if desired. Now create and bake the simulation.

External resources

 * Gentoo specific build instructions for Blender from Blender Wiki