Fixed grid header row/column

[PPakalns]

Similar to this codepen example. https://codepen.io/neoky/pen/mGpaKN

Is it possible to make sticky column, header in display: Grid, overflow: Scroll elements.

It seems that it is dependent on last element that is scroll-able and what scroll offset it has.
Technically it looks like i could store "stickiness" flag as metadata and I just shouldn't apply scroll offset to element and it would be drawn correctly. If this is all that is required, could taffy add position: sticky and add a flag to layout if it should be sticky?

Is there another way to achieve sticky header column/row in grid?

[PPakalns]

Got behavior similar to position: sticky working in egui_taffy by manually storing sticky flag for nodes.

sticky_grid_demo.mov

[nicoburns]

Technically it looks like i could store "stickiness" flag as metadata and I just shouldn't apply scroll offset to element and it would be drawn correctly. If this is all that is required, could taffy add position: sticky and add a flag to layout if it should be sticky?

So I think the "correct" computation for position: sticky is a little more complicated than just not applying the scroll offset:

1. It should conditionally not apply the scroll offset once the item would otherwise scroll out of view
2. The position at which the "sticky" position takes effect should be inset by the top/left/bottom/right styles.
3. There might need to be some kind of conflict resolution for over-constrained cases (e.g. container is smaller than sticky node or sticky node has both bottom and top set)

But, as you have demonstrated:

• (1) doesn't apply if the initial (static) position of the node is 0
• (2) doesn't apply if the sticky position is 0
• (3) doesn't apply if the container is big enough and only one property is each axis is set

---

I don't think it makes sense to have position: sticky as part of the main layout phase in Taffy, because position: sticky is scroll position dependent, and you don't want to have to recompute layout every time the scroll position changes. But:

• There could be a helper which computes the position given inputs (which would be called manually)
• It could potentially be incorporated as part of a (new) phase that could:
  • Compute position: sticky
  • Apply transform

I'd probably want to start with the former approach and move towards the latter once I/we are more sure how it needs to work.

[PPakalns]

Thank you for the detailed explanation.

If better support for scrollable elements and position: sticky is added to taffy in future, helper functions would be very useful to correctly handle scrolling and position: sticky.

At least for basic case simple sticky flag for now works good enough in egui_taffy. Thank you all for this great project.