Mesa's off-screen rendering interface is used for rendering into user-allocated Ruby string. That is, the GL_FRONT colorbuffer is actually a buffer in main memory, rather than a window on your display. There are no window system or operating system dependencies. One potential application is to use Mesa as an off-line, batch-style renderer.

The OSMesa API provides two basic functions for making off-screen renderings: OSMesa::Context.new() and OSMesa::Context#MakeCurrent(). See API-docs for more information about the API functions.

Install osmesa library and header files:

• on Ubuntu/Debian:

$ sudo apt-get install libosmesa6-dev

• on Windows: No need to install dependencies - the binary gem includes everything

Install the gem:

$ gem install osmesa

Use OSMesa to create an offline rendering buffer and use the opengl gem to render a red line. The raw RGBA image buffer is written to a PNG image file with the help of the chunky_png gem:

require 'osmesa'
require 'opengl'
require 'chunky_png'
width, height = 100, 70
ctx = OSMesa::Context.new(OSMesa::RGBA, nil)
buffer = "rgba" * width * height
ctx.MakeCurrent(buffer, GL::GL_UNSIGNED_BYTE, width, height)
GL.implementation = OSMesa::Implementation.open
GL.MatrixMode(GL::GL_MODELVIEW)
GL.LoadIdentity()
GL.Clear(GL::GL_COLOR_BUFFER_BIT)
GL.Color4ub(0xff, 0x00, 0x00, 0xff)
GL.Begin(GL::GL_LINES)
GL.Vertex(0.5, 0.5)
GL.Vertex(-0.5, -0.5)
GL.End
GL.Flush()
png = ChunkyPNG::Image.from_rgba_stream(width, height, buffer)
png.save('test.png')

This project makes use of rake-compiler-dock for building binary Windows gems. This is done by the following rake task:

$ rake gem:windows

After download and compile, there should be some files in the pkg directory: pkg/osmesa-{VERSION}-{PLATFORM}.gem

1. Fork it ( https://github.com/larskanis/osmesa/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request