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Adjust scroll offset with relative scrolling #4166

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merged 3 commits into from
Mar 3, 2020
Merged

Adjust scroll offset with relative scrolling #4166

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f9d2d45
use relative scrolling to compensate when changing height
bwindels Mar 3, 2020
223956a
add comment how offset from bottom is calculated
bwindels Mar 3, 2020
3e39ceb
also use relative scrolling when eh ... doing relative scrolling
bwindels Mar 3, 2020
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17 changes: 8 additions & 9 deletions src/components/structures/ScrollPanel.js
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Original file line number Diff line number Diff line change
Expand Up @@ -523,7 +523,7 @@ export default createReactClass({
scrollRelative: function(mult) {
const scrollNode = this._getScrollNode();
const delta = mult * scrollNode.clientHeight * 0.5;
scrollNode.scrollTop = scrollNode.scrollTop + delta;
scrollNode.scrollBy(0, delta);
this._saveScrollState();
},

Expand Down Expand Up @@ -705,17 +705,15 @@ export default createReactClass({
// the currently filled piece of the timeline
if (trackedNode) {
const oldTop = trackedNode.offsetTop;
// changing the height might change the scrollTop
// if the new height is smaller than the scrollTop.
// We calculate the diff that needs to be applied
// ourselves, so be sure to measure the
// scrollTop before changing the height.
const preexistingScrollTop = sn.scrollTop;
itemlist.style.height = `${newHeight}px`;
const newTop = trackedNode.offsetTop;
const topDiff = newTop - oldTop;
sn.scrollTop = preexistingScrollTop + topDiff;
debuglog("updateHeight to", {newHeight, topDiff, preexistingScrollTop});
// important to scroll by a relative amount as
// reading scrollTop and then setting it might
// yield out of date values and cause a jump
// when setting it
sn.scrollBy(0, topDiff);
debuglog("updateHeight to", {newHeight, topDiff});
}
}
},
Expand Down Expand Up @@ -767,6 +765,7 @@ export default createReactClass({
},

_topFromBottom(node) {
// current capped height - distance from top = distance from bottom of container to top of tracked element
return this._itemlist.current.clientHeight - node.offsetTop;
},

Expand Down