components: ReorderableColumn drag shadow follows the card

components/src/main/kotlin/de/jeanlucmakiola/floret/components/ReorderableColumn.kt

@@ -11,7 +11,6 @@ import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.height
-import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.derivedStateOf
 import androidx.compose.runtime.getValue
@@ -21,10 +20,18 @@ import androidx.compose.runtime.remember
 import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.geometry.Size
+import androidx.compose.ui.geometry.translate
+import androidx.compose.ui.graphics.Outline
+import androidx.compose.ui.graphics.Path
+import androidx.compose.ui.graphics.Shape
 import androidx.compose.ui.graphics.graphicsLayer
 import androidx.compose.ui.input.pointer.pointerInput
 import androidx.compose.ui.platform.LocalDensity
+import androidx.compose.ui.unit.Density
 import androidx.compose.ui.unit.Dp
+import androidx.compose.ui.unit.LayoutDirection
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.zIndex
 import kotlinx.coroutines.Job
@@ -53,7 +60,8 @@ private val RowGap: Dp = 2.dp
  * [GroupedRow]'s card shaping — pass `gapBelow = false` there, this owns spacing)
  * and a `dragHandle` [Modifier] to attach to the element that starts a drag.
  * Pass [rowHeight] matching the rows' non-reorder `minHeight`, so they keep their
- * size when a screen switches into reordering.
+ * size when a screen switches into reordering. [rowInset] is the card's horizontal
+ * inset inside its slot, so the held row's shadow hugs the card, not the slot.
  */
 @Composable
 fun <T> ReorderableColumn(
@@ -62,6 +70,7 @@ fun <T> ReorderableColumn(
     onReorder: (List<T>) -> Unit,
     modifier: Modifier = Modifier,
     rowHeight: Dp = ReorderableRowHeight,
+    rowInset: Dp = GroupedListInset,
     rowContent: @Composable (item: T, position: Position, dragHandle: Modifier, isDragging: Boolean) -> Unit,
 ) {
     val pitchPx = with(LocalDensity.current) { (rowHeight + RowGap).toPx() }
@@ -174,7 +183,7 @@ fun <T> ReorderableColumn(
                             scaleX = 1.02f
                             scaleY = 1.02f
                             shadowElevation = 8.dp.toPx()
-                            shape = RoundedCornerShape(20.dp)
+                            shape = InsetShape(groupedShape(positionOf(index, order.size), 22.dp, 6.dp), rowInset)
                             clip = false
                         }
                     },
@@ -184,3 +193,16 @@ fun <T> ReorderableColumn(
         }
     }
 }
+
+/** [base] laid out [inset] in from both sides of the slot. */
+private class InsetShape(private val base: Shape, private val inset: Dp) : Shape {
+    override fun createOutline(size: Size, layoutDirection: LayoutDirection, density: Density): Outline {
+        val dx = with(density) { inset.toPx() }
+        val inner = Size((size.width - 2 * dx).coerceAtLeast(0f), size.height)
+        return when (val outline = base.createOutline(inner, layoutDirection, density)) {
+            is Outline.Rectangle -> Outline.Rectangle(outline.rect.translate(Offset(dx, 0f)))
+            is Outline.Rounded -> Outline.Rounded(outline.roundRect.translate(Offset(dx, 0f)))
+            is Outline.Generic -> Outline.Generic(Path().apply { addPath(outline.path, Offset(dx, 0f)) })
+        }
+    }
+}