Displaying a few hundreds widgets has absolutely negligible cost if the code is written properly. For large lists they can always be clipped and not submitted a

Displaying a few hundreds widgets has absolutely negligible cost if the code is written properly. For large lists they can always be clipped and not submitted at all. With an immediate-mode GUI you can actually handle navigation of a list of one million items whereas more RMGUI would struggle because of all the intermediate data involved. Also, the optimization bottleneck nowadays is mostly programmer/brain time, so having a ten-fold productivity improvements means you can actually create more/better tooling and that has very direct consequence on your software performance. The reality with toolkits like QT is that people write very little amount of tooling with it, because it is so tedious. The cost of that are lost opportunity in improving a game engine and its performances.