Sublime Text 1 used OpenGL (1.1 only, hence no GLEW) and Direct3D, while 2 and 3 are mostly software only.

While Sublime Text 2 and 3 do use Skia, only a tiny fraction of its functionality is actually used, just for rasterizing lines and blitting images. Font rendering is done by using the underlying platform APIs to do the glyph rasterisation.