Yes, it's actually the same principle behind using CSS instead of images on a website. Pretty common these days to avoid loading a lot of extra assets when the CSS file can contain everything, and often for much lower overhead when the heavy work of actually rendering many shapes and features is already set up in the rendering engine, and you just need a few text bytes to tell it what to do. Plus, a system like that could scale infinitely to any resolution. The only graphics type that could claim to have that ability is SVG, which is already a text file format anyway. I just have no idea how performant using libRocket to render HUD elements in real time could actually be. Although there might be a middle ground, using libRocket during game/mission load to render HUD assets into memory at the specified resolution.