> I don’t understand why free software always neglects the UI.
Because most programmers aren’t very good at it and because it’s hard. For example, suppose you add a very simple parameter like setting the diameter of a circle. Internally that code is probably pretty simple. Once you expose it to users, you have an enormous amount of ground to cover. A few examples would include:
* How to handle a cancellation, such as the after pressing escape. Dismiss the dialogue? What if there are other settings in the same dialogue with newly altered values? Cancel the whole thing and lose other input or what?
* Undo, perhaps multilevel. If multilevel undo, do you set the number of levels yourself or do you allow that to be configured via a separate settings dialogue? Limit to memory or some fixed number of steps? Once saved, do you save those values in the user application data space, environment variables, a real database, the local directory, a hidden directory, or some combination of all these?
* Constraining input. You may not be dealing with keyboard input exclusively. Maybe you decide to let dragging the mouse set that value. Or maybe you want the up and down arrow keys to work, in which case you need to set an increment. Maybe that increment needs to be reflected in a Settings dialogue.
* What about units? Should they be integer, big integer, or float? Percentage or pixels or centimeters or inches?
* Accessibility. If voice input, do you come up with a of vocabulary of your commands for your app? If for limited range of motion, how do you design the dialogue to be visually attractive and not too cluttered but still useful for someone who can only move the pointing device a few millimeters at a time? What kind of color themes are accessible for the dialogue and the rest of the app? should these be supplied by the operating system or should you include color configurations as part of your app?
* How does the host OS handle flexible dialogue sizes and responsive screen size, if at all? Who does the UX for the mobile version? iOS only or also include android support?