Incorrect calculation of nextOffsetY

[Hooked74]

When recalculating nextOffsetY when popup goes beyond the viewport boundaries incorrect calculations occur. I see problems in these lines: https://github.com/react-component/trigger/blob/a73beef20376e3e32ecb918a0c1fbb0cdabb42f3/src/hooks/useAlign.ts#L313 https://github.com/react-component/trigger/blob/a73beef20376e3e32ecb918a0c1fbb0cdabb42f3/src/hooks/useAlign.ts#L327

Let's analyze each line separately.

---

nextOffsetX = targetAlignPointTL.x - popupAlignPointBR.x - popupOffsetX; 

suppose the target's bounding box is

{
  width: 200px
  left: 300px
  right: 500px
}

the popup's bounding box is

{
  width: 600px
  left: 0px
  right: 600px
}

first popup calculation without flip recalculation

{
  width: 600px
  left: 300px
  right: 900px
}

x viewport border for example is 600px Our popup climbs out of the border, so we implement the recalculation of nextOffsetX. targetAlignPointTL.x = 300px popupAlignPointBR.x = 600px popupOffsetX = 0 nextOffsetX = 300px - 600px - 0 = -300px

Total we get that our popup left offset is -300px and right 600px - 300px = 300px And we observe approximately the following picture

In order to get the correct offset, you need to subtract the right coordinate of popup not from the left coordinate of the target, but from the right. In other words, change targetAlignPointTL to targetAlignPointBR and get

nextOffsetX = targetAlignPointBR.x - popupAlignPointBR.x - popupOffsetX; 

---

The situation is similar with Left to Right

nextOffsetX = targetAlignPointBR.x - popupAlignPointTL.x - popupOffsetX;

if we take fake data target bb

{
  width: 200px
  left: 100px
  right: 300px
}

popup bb

{
  width: 500px
  left: 0px
  right: 500px
}

popup calculated bb

{
  width: 500px
  left: -200px
  right: 300px
}

viewport left border 0px popupOffsetX = 0px then substituting into the current formula we get nextOffsetX = 300px - 0px - 0px = 300px

Popup offset is 300px this is the right border of the target. Why not just take the left offset of target and make it equal to nextOffsetX? Well, or as a last resort, add the right border of the target to the existing offset nextOffsetX = nextOffsetX + targetAlignPointBR.x = -200px + 300px = 100px We will get the same 100px

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In general, the problem is on the face and it brings a lot of inconvenience. Please pay attention to it!