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Keep still the end of a row nearest the tap, not the control pressed

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Everything that opens now behaves alike. Touch a row's upper half and its
top edge holds, so it opens and closes downwards; touch the lower half and
the bottom edge holds, which is what the list does on its own. A group's
heading and the bar at its foot fall in the halves they already occupy, so
they keep the behaviour they had, and a single tool call -- one card, with
no bar -- gets the same choice for the first time: tapping low on an open
Bash card now shuts it downwards exactly as a group's bar does.

That makes the position of the tap the one mechanism, and RowEdge goes
away with the pair of hardcoded ends it existed to name. Controls report
where they were touched in root coordinates, which is all a control can
know -- a group is one row with a control at each end and calls in the
middle, and only the row knows where its own ends are -- and the row turns
that into an edge.

`clickableAt` is built on `clickable` rather than replacing it, so the
ripple and the click action assistive technology reads are unchanged; the
down position is observed on the initial pointer pass and nothing is
consumed.

Verified with ui-trace: on a collapsed group, a tap at y=1370 holds the
heading and one at y=1450 lets the row grow upward instead. On the same
nested call inside an open group, opening it from the group's upper half
holds the heading at 565 and from the lower half moves it to 296. ktfmt,
lint and 85 tests clean.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
irisandClaude Opus 5 committed 2026-08-30 12:29:41 -04:00
1 parent 5eba6ec529
commit 30ebf4e25c
4 files changed
+108 -54
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app/androidApp/src/main/kotlin/com/example/aiapp/SessionScreen.kt
+54 -28
View File
@@ -47,7 +47,9 @@ import androidx.compose.runtime.setValue
import androidx.compose.runtime.snapshotFlow
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.layout.onGloballyPositioned
import androidx.compose.ui.layout.onSizeChanged
import androidx.compose.ui.layout.positionInRoot
import androidx.compose.ui.platform.LocalContext
import androidx.compose.ui.semantics.contentDescription
import androidx.compose.ui.semantics.semantics
@@ -94,6 +96,21 @@ private class TopEdgeHold {
var key: Any? = null
}
/**
* Where a row is on screen, so a tap on it can be told which half it landed in.
*
* Not snapshot state, for the same reason as [TopEdgeHold]: written from layout, read from a click,
* and observed by nothing.
*/
private class RowBounds {
var top = 0f
var height = 0f
/** Above this is the row's top half, below it the bottom half. */
val middle
get() = top + height / 2
}
/** One row's height between layouts, so a change in it can be noticed. See [holdTopEdge]. */
private class LastHeight {
var value: Int? = null
@@ -718,21 +735,25 @@ fun SessionScreen(
}
/**
* Changes a row's height while the end the reader pressed stays where it is.
* Changes a row's height while the end the reader touched stays where it is.
*
* The transcript is laid out from the bottom, so every row's *bottom* edge is what the list
* holds still and all growth goes upward. That is right for the bar at the foot of an open
* group -- shut it from there and what follows it does not move, which is what the reader is
* looking at. It is exactly wrong for a heading: opening a group from the top sends the heading
* up off the screen and fills the space above it, so the calls appear on the far side of the
* control that produced them.
* holds still and all growth goes upward. That is what a tap in a row's lower half already
* gets, so it needs nothing: shut a group from the bar at its foot and what follows it does not
* move, which is what the reader is looking at down there. A tap in the upper half is the other
* case -- left alone it sends the heading under the reader's finger up off the screen and fills
* the space above it, so the calls appear on the far side of the control that produced them --
* and that one asks the row to hold its top edge instead.
*
* So [RowEdge.Bottom] is the list's own behaviour and needs nothing, while [RowEdge.Top] marks
* the row as holding its top edge the next time it is measured. The correction itself belongs
* to the measurement -- see [holdTopEdge].
* Which half decides it, rather than which control was pressed, so that everything that opens
* behaves the same way whether or not it happens to have a control at each end. A group has two
* and its heading and foot bar land in the halves they are already in; a single call is one
* card, and tapping low on an open one shuts it downward exactly as the bar does.
*
* The correction itself belongs to the measurement -- see [holdTopEdge].
*/
fun toggleAnchored(key: Any, edge: RowEdge, toggle: () -> Unit) {
if (edge == RowEdge.Top) topEdgeHeld.key = key
fun toggleAnchored(key: Any, row: RowBounds, at: Float, toggle: () -> Unit) {
if (at < row.middle) topEdgeHeld.key = key
toggle()
}
@@ -1187,24 +1208,29 @@ fun SessionScreen(
// at the same end. Paging older history is the opposite insertion and was
// already fine, and stays fine, because a key survives both.
items(rows.asReversed(), key = { it.key }) { row ->
val bounds = remember { RowBounds() }
Box(
Modifier.holdTopEdge(row.key, topEdgeHeld) { grew ->
// Requested rather than scrolled. Scrolling forces a remeasure,
// and forcing one from inside a measure throws; this is the form
// built to be asked for during layout and applied in that pass.
listState.requestScrollToItem(
listState.firstVisibleItemIndex,
listState.firstVisibleItemScrollOffset + grew,
)
}
Modifier.onGloballyPositioned {
bounds.top = it.positionInRoot().y
bounds.height = it.size.height.toFloat()
}
.holdTopEdge(row.key, topEdgeHeld) { grew ->
// Requested rather than scrolled. Scrolling forces a remeasure,
// and forcing one from inside a measure throws; this is the form
// built to be asked for during layout and applied in that pass.
listState.requestScrollToItem(
listState.firstVisibleItemIndex,
listState.firstVisibleItemScrollOffset + grew,
)
}
) {
when (row) {
is TranscriptRow.Tools ->
ToolGroup(
group = row,
expanded = row.id in expandedGroups,
onToggle = { edge ->
toggleAnchored(row.key, edge) {
onToggle = { at ->
toggleAnchored(row.key, bounds, at) {
expandedGroups =
if (row.id in expandedGroups)
expandedGroups - row.id
@@ -1215,8 +1241,8 @@ fun SessionScreen(
// Anchored on the group, not the call: opening one call makes
// the whole group taller, and the heading the reader is under
// is the group's.
onToolToggle = { id ->
toggleAnchored(row.key, RowEdge.Top) {
onToolToggle = { id, at ->
toggleAnchored(row.key, bounds, at) {
expandedTools =
if (id in expandedTools) expandedTools - id
else expandedTools + id
@@ -1248,8 +1274,8 @@ fun SessionScreen(
ToolCard(
tool = item,
expanded = item.id in expandedTools,
onToggle = {
toggleAnchored(row.key, RowEdge.Top) {
onToggle = { at ->
toggleAnchored(row.key, bounds, at) {
expandedTools =
if (item.id in expandedTools)
expandedTools - item.id
@@ -1302,8 +1328,8 @@ fun SessionScreen(
PeerMessageRow(
item = item,
expanded = item.seq in expandedNotes,
onToggle = {
toggleAnchored(row.key, RowEdge.Top) {
onToggle = { at ->
toggleAnchored(row.key, bounds, at) {
expandedNotes =
if (item.seq in expandedNotes)
expandedNotes - item.seq