> But at what cost? 100% CPU and GPU usage, tons of system/video memory.
Games use lots of CPU/GPU resources because they're rerendering all the time. You don't do that in GUI apps. You also don't have huge swaths of 3d assets.
> Also, rendering text with full capabilities (arbitrary font/size/color, emoji, ...) is much more complicated than drawing a textured polygon.
That's exactly how text is rendered: Glyphs cached into textures that are blitted. Filling the cache is a little more involved, but you're not doing that all the time.
> And how easy is to use a modern 3D engine versus HTML/CSS?
You don't need to use a game engine; traditional GUI toolkits did this stuff out of necessity due to much slower hardware available at the time.
Games use lots of CPU/GPU resources because they're rerendering all the time. You don't do that in GUI apps. You also don't have huge swaths of 3d assets.
> Also, rendering text with full capabilities (arbitrary font/size/color, emoji, ...) is much more complicated than drawing a textured polygon.
That's exactly how text is rendered: Glyphs cached into textures that are blitted. Filling the cache is a little more involved, but you're not doing that all the time.
> And how easy is to use a modern 3D engine versus HTML/CSS?
You don't need to use a game engine; traditional GUI toolkits did this stuff out of necessity due to much slower hardware available at the time.