Hold the FAB still while the selection bar unfolds (#141)

app/src/main/java/de/jeanlucmakiola/calendula/ui/common/CalendarFabColumn.kt

@@ -11,6 +11,8 @@ import androidx.compose.animation.shrinkHorizontally
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.wrapContentHeight
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.automirrored.filled.KeyboardArrowRight
 import androidx.compose.material.icons.filled.Add
@@ -26,6 +28,7 @@ import androidx.compose.runtime.Composable
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.unit.dp
 import de.jeanlucmakiola.calendula.R
@@ -39,6 +42,9 @@ class FabSelection(
 
 private enum class FabIcon { Create, Open, Fold }
 
+/** The standard FAB's size, which the row it sits in is held to. */
+private val FAB_SIZE = 56.dp
+
 /**
  * The FAB stack shared by the three calendar views: a persistent "+" to
  * create an event, with the jump-to-today pill appearing above it whenever
@@ -73,12 +79,17 @@ fun CalendarFabColumn(
         // Held past the selection clearing, so the bar has something to fold away.
         val heldBar = remember { mutableStateOf<(@Composable () -> Unit)?>(null) }
         selection?.let { heldBar.value = it.bar }
+        // Held at the FAB's own height whatever the bar does: the bar is taller,
+        // and a row grown to fit it moved the FAB up as the bar unfolded.
         Row(
+            modifier = Modifier.height(FAB_SIZE),
             verticalAlignment = Alignment.CenterVertically,
             horizontalArrangement = Arrangement.spacedBy(8.dp),
         ) {
             AnimatedVisibility(
                 visible = selection?.expanded == true,
+                // Overflows the row evenly above and below, centred on the FAB.
+                modifier = Modifier.wrapContentHeight(unbounded = true),
                 enter = expandHorizontally(
                     animationSpec = MaterialTheme.motionScheme.fastSpatialSpec(),
                     expandFrom = Alignment.End,