MICROPOLIS

Micropolis is a micropolygon render implemented in OpenCL.

It uses the REYES[1] algorithm to rasterize curved surfaces. This is done by splitting the surface into sub-pixel sized polygons (micropolygons) and rasterizing them. Doing so allows the rendering of highly detailed, displaced surfaces.

The subdivision, dicing, shading and rasterization of the micropolygons is implemented in OpenCL. The rasterizer fills a framebuffer that is then rendered as texture in OpenGL. There also exists an alternative render backend that uses OpenGL hardware tessellation for performance comparison.

Here is a video of it in action: Video

COMPILATION

You will need the following dependencies to build micropolis on Linux:

• SCons
• GLFW 3.0
• Boost
• OpenCL
• DevIL
• Python 3.x
• Wheezy template
• Cap'n Proto

The source uses some C++11 features, so you need a version of GCC recent enough to support this.

To build call:

$ git submodule init
$ git submodule update
$ scons

The build-system uses code-generation for creating the config-file parser and the OpenGL extension loader. This is done by two Python programs(configGen and flextGLgen) in the tools directory. They reside in separate git submodules, so it is necessary to initialize and update them before compiling with SCons.

USAGE

Just call:

$ ./micropolis

You will see performance statistics on the command line.

• Q or ESC close the application
• Use WASD to move the camera
• LMB+drag rotates the camera
• MMB+drag moves the camera on the eye plane
• RMB+drag rotates the camera along the z axis
• PGUP/PGDOWN controls target patch size for Bound&Split algorithm
• F3 toggles wireframe mode
• F9 dumps a trace file which can be visualized using tools/show_trace.sh
• F12 saves the current camera position as an mscene file
• PRINT creates a screenshot

You can configure the program by modifying the *.options configuration files. The files are pretty well-documented.

Interesting configuration-values are:

• input_file: The scene to render. Look in the mscene/ dir for scene files.

• opencl_device_id: A pair of numbers giving platform and device id of the OpenCL device that should be used.

• reyes_patches_per_pass: Sets how many sub-patches are diced and rasterized at once. Larger batches require more OpenCL device memory and take longer. Smaller batches have more overhead. You should set something between 256 and 4096. Use powers of two.

• bound_n_split_method: The method used for bound and split. Can be BOUNDED, LOCAL, BREADTH, or CPU

• bound_n_split_limit: In the first step of REYES, all patches are split to this screen size.

• reyes_patch_size: The horizontal and vertical dicing rate of the split subpatches. Should ideally be the same as bound_n_split_limit to get pixel-sized micropolygons. More is a waste. Needs to be divisible by 8.

LIMITATIONS

Micropolis is very much a prototype. It is limited in several ways:

• Surface patches are diced at a fixed rate This can lead to wasteful overtessellation

• Surface cracks are not handled This can result in holes between surface patches.

• Micropolygons are always flat-shaded Gouraud shading would result in fewer artifacts.

• No Multisampling or stochastic rasterization is supported

• Surface shader and displacement are hard-coded in the OpenCL kernel

These problems may be fixed in the future. The first three issues will probably be solved by using DiagSplit and decoupled shading.

REFERENCES

[1] "The Reyes image rendering architecture", H.L. Cook, L. Carpenter, E. Catmull Computer Science Press, Inc. New York, NY, USA, 1988

COPYRIGHT & LICENSE

Copyright Thomas Weber 2011-2014

Micropolis is licensed under the GPLv3.