Shaderboy

Shaderboy is an application and library to render OpenGL shaders on LED panels and cubes. It is optimized for and coupled to the Raspberry Pi and the iCEBreaker FPGA.

Shaderboy draws inspiration from Shadertoy and Shady.

Installation

$ make && sudo make install

Where's the Eye Candy?

Most of the demos are in the shaders directory.

cd shaders
for demo in *.glsl
do
    shaderbox --duration=10 $demo
done

Some additional demos are in the scripts directory.

Architecture

Shaderboy has several public APIs: Linux CLI, Python, and C.

Command line

At the highest level, the shaderbox command renders a fragment shader written in the OpenGL Shading Langues (GLSL) on the LEDs.

$ echo 'void main() { gl_FragColor = vec4(1); }' | shaderbox

or

$ shaderbox myfile.glsl

or, if you remember Unix,

$ head -n 1 myfile.glsl
#!/usr/bin/env shaderbox
$ chmod +x myfile.glsl
$ ./myfile.glsl

Python API

You can also use Shaderboy from Python programs using the shade module. See the scripts subdirectory for examples.

C API

You can use Shaderboy from C programs using the libshade library. See c/test/ltest.c for an example.

GLSL extensions

The Raspberry Pi uses GLSL 1.0. Shaderboy adds some extensions via a preprocessor.

Predefined Variables

To be documented. Similar to Shadertoy's. iResolution, iTime, iFrame are implemented.

Alternate Entrypoints

To be documented. Similar to Shady's. main, mainImage, mainCube are implemented.

Pragmas

To be documented. Similar to Shady's.

    #pragma use [filename]
    #pragma map [variable]=image:[filename]
    #pragma map [variable]=builtin:[builtin]
    #pragma map [variable]=perip_map4:[device]

Optimization

Shaderboy creates three threads and does all rendering in those threads. Rendering is asynchronous with the calling thread. On a four core Raspberry Pi, one core is never blocked by rendering.

• The render thread invokes the GPU to render pixels on screen. This uses OpenGL.

• The cmd thread repackages pixels as commands for the FTDI chip on the iCEBreaker board.

• The output thread sends commands to the iCEBreaker via the Raspberry Pi's USB interface.

The render thread may be CPU or GPU bound. The output thread is usually waiting on the FTDI chip. And the cmd thread is there to offload and decouple the other two threads so they can always run.