It not even a drawing API, even. It's a 3D triangle rendering API. Things like lines, bezier curves, gradients are all do-it-yourself. None of it super-hard, I've done them all, but before you write your UI you have to write all your drawing routines, which probably wasn't what you wanted to be doing. And you get all the fun texture management issues for any gradients and images you want to display. And you probably won't have optimized it like the platform rendering will have.

And then there's text... You've got to load a texture for every glyph of every point size used in the app for every font used in the app. Mind you, the OS already has a cache for this, but you don't have access to it, so that's more memory wasted. Which would be sizeable if every app on your system was using Japanese, or worse, Chinese, and making a copy of all this stuff.

This is a very good point that I feel gets overlooked way too often. When people talk about the UI feeling sluggish most of the time they are talking about responsiveness.

Like, who cares if your app is rendering at 120 fps if it takes me 3 seconds to focus on a text field? I feel like that’s where most cross platform tooling has their work cut out.

Hi Paul, not sure if this an appropriate place to mention this but I hope you please consider at some point using OpenGL or Vulkan to at least render the track view in Ardour. I have a large project with around 50 tracks that is extremely slow and laggy to render when zoomed all the way out, it is making the program unusable for me. I could provide a profile to put in a bug report but I'm not sure the best way to go about that. Thanks.