Once Virtools Dev Users asked for Shader-Authoring using graphs … in meanwhile we not only saw such technology used in a couple of other engines (i.e. offset engine, Unreal3 engine) but also in products like the one from Lumonix or the discontinued RTZen's Ginza and ShaderWorks. (which btw. was inspired by ShaderMan for RenderMan). Now there will be another product aaaaand …. it will be for free …
Mental Mill Artists Edition
More info on CGSociety. The product is also mentioned in the GDC FXComposer2_PDF. Moreover you can get information from the creators directly: Mental Images
