Libui: [POLL] Should single-child containers (uiWindow, uiGroup, uiTab pages) allow NULL children?

[andlabs]

Containers that allow only one child — uiWindow, uiGroup, and the individual pages of a uiTab — have this weird intermediary state when you first create them: the state of having no child; the value of the child uiControl pointer is NULL. This creates a bunch of weird edge cases for determining what the preferred size of these containers should be and certain grandparent-parent-child relationships.

There are three things I can do to resolve this:

1) Allow NULL children explicitly where passing NULL to a SetChild() will simply produce an empty container.
2) Allow NULL initially, but not afterward where creating a container has a NULL child but that's the only time NULL is allowed
3) Disallow NULL entirely meaning that every constructor function would need you to pass a child in, even a temporary one like an empty box (I could provide a spacer control too)

What do you all think? I'm genuinely not sure which I should do; all the options require relatively the same amount of code effort on my part.

[zevv]

I opt for option 1.

Containers which take N children (Box, Tabs) also allow to be in an empty state, so why not also allow this for containers with a single state? This is also a bit more friendly and flexible from the API users' perspective, as it allows for more flexible construction and tear down of a control hierarchy.

[zevv]

Also, referring to my other issue with manually tearing down a control tree: not allowing NULL children would make it impossible to remove an object from a tree from the leaves down.

[marcomorain]

Another option would be to disallow NULL and instead have a new control
type uiEmptyControl that has no size and is not rendered. single child
containers could have this set as the child when they are constructed.

On Mon, 23 May 2016, at 08:43, Ico Doornekamp wrote:

Also, referring to my other issue with manually tearing down a control
tree: not allowing NULL children would make it impossible to remove an
object from a tree from the leaves down.
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Links:

1. https://github.com/andlabs/libui/issues/48#issuecomment-220908879

[gnarz]

I'd vote for option 1, as this creates symmetry with multi child controls.

[dfyx]

Option 1 feels the most intuitive.

[andlabs]

Multi-child controls don't allow you to add NULL, as that would make little sense (the only use would be uiBoxAppend(NULL, stretchy = true) for stretchy blank space; and later leaving a grid cell blank, but not specifying that cell is the same). If they're empty, they're empty.

uiEmptyControl could probably just be an empty box internal to these containers. The original package ui had ui.Space(), a function that returned such a thing for the purpose of stretchy blank space.

[SevenBits]

Option 1 is the best IMO.

[andlabs]

Current idea:

Allow NULL everywhere, including uiBox and uiGrid; implicitly turn it into a dummy empty-space control. Ownership has to be maintained by the parent, but that shouldn't be too hard.

How does this sound?

[andlabs]

Merged with #328.