Using geometry shader allows us to get rid of the 'line origin' extra vertex attribute, which means dashed shader no longer requires fiddling with those vertex attributes definition, and, most importantly, does not require anymore special drawing code! As you can see, this makes code much simpler, and much less verbose, especially in complex cases. In addition, changed how dashes are handled, to have two 'modes', a simple one with single color (using default "color" uniform name), and a more advanced one allowing more complex and multi-color patterns. Note that since GLSL 1.2 does not support geometry shaders, a hack was added for now (which gives solid lines, but at least does not make Blender crash).