The biggest issue with GUI programming is always "when to reflow" and "when to relayout".
Take fading in sidebars, for example, which influence how the main content frame is rendered and are different in size on mobiles (e.g. icons, icons with labels, bigger icons, bigger labels or even a more nested structure on desktop, with a burger icon for fade-in and fade-out).
This is almost impossible to implement if you only have horizontal and vertical box layouting at your disposal, which is the most common denominator among frameworks and their renderer concepts (GTK, Springs, QT, etc).
Flexbox and tweenable properties like transparency, rounded corners, margins, paddings, colors and z-indexes are almost a hard requirement these days in terms of UI design. And those features are very hard to implement without a renderer pipeline that can influence both fragment and vertex shaders.
And this is not talking about state management of the UI elements, which is a whole world of problems on its own. React Native's approach, for example, is utterly broken on older mobiles due to how they re-flush the whole state tree on every single frame (which makes old mobiles lag due to them not being able to keep up with the amount of FPS required).
Getting the reflow right with e.g. calendar widgets and calendar popup views which are rendered by native APIs is a nightmare. As there is no unified way to do it across platforms, there eventually will be a lot of redundancies that are implemented, and a whole lot of quirky code behavior.
Plus, there are some wrappers that make seamless transition between desktop and mobile view like MauiKit[2] and Kirigami[3]. I don't think they're perfect or that they are doing it correctly even, but they're onto something with their main idea.
Take fading in sidebars, for example, which influence how the main content frame is rendered and are different in size on mobiles (e.g. icons, icons with labels, bigger icons, bigger labels or even a more nested structure on desktop, with a burger icon for fade-in and fade-out).
This is almost impossible to implement if you only have horizontal and vertical box layouting at your disposal, which is the most common denominator among frameworks and their renderer concepts (GTK, Springs, QT, etc).
Flexbox and tweenable properties like transparency, rounded corners, margins, paddings, colors and z-indexes are almost a hard requirement these days in terms of UI design. And those features are very hard to implement without a renderer pipeline that can influence both fragment and vertex shaders.
And this is not talking about state management of the UI elements, which is a whole world of problems on its own. React Native's approach, for example, is utterly broken on older mobiles due to how they re-flush the whole state tree on every single frame (which makes old mobiles lag due to them not being able to keep up with the amount of FPS required).
Getting the reflow right with e.g. calendar widgets and calendar popup views which are rendered by native APIs is a nightmare. As there is no unified way to do it across platforms, there eventually will be a lot of redundancies that are implemented, and a whole lot of quirky code behavior.