web/src/plan/PlanPage.test.tsx

@@ -1035,13 +1035,14 @@ describe.each([
   const float = () => screen.queryByTestId('drag-float')
 
   // press, move and release drive pointer 3 on the draggable: down at
-  // (100, 100), moved over an element (or none), and let go there.
+  // (100, 100), moved over an element (or none) at (160, 140) or the given
+  // point, and let go there.
   function press(draggable: Element) {
     fireEvent.pointerDown(draggable, { pointerId: 3, isPrimary: true, button: 0, clientX: 100, clientY: 100 })
   }
-  function move(draggable: Element, over: Element | null) {
+  function move(draggable: Element, over: Element | null, [clientX, clientY] = [160, 140]) {
     hovered = over
-    fireEvent.pointerMove(draggable, { pointerId: 3, isPrimary: true, clientX: 160, clientY: 140 })
+    fireEvent.pointerMove(draggable, { pointerId: 3, isPrimary: true, clientX, clientY })
   }
   function release(draggable: Element) {
     fireEvent.pointerUp(draggable, { pointerId: 3, isPrimary: true, button: 0, clientX: 160, clientY: 140 })
@@ -1079,6 +1080,10 @@ describe.each([
     expect(declaredStyle(copy).boxShadow).toBe('var(--shadow-lg)')
     expect(declaredStyle(copy).transform).toBe('rotate(-3deg)')
     expect(declaredStyle(copy).pointerEvents).toBe('none')
+    // Offset 48 px below right of the pointer at (160, 140), clear of the
+    // day's text under it.
+    expect(copy.style.left).toBe('208px')
+    expect(copy.style.top).toBe('188px')
     expect(announcer()).toHaveTextContent('Picked up Lemon orzo.')
     const target = within(column('Friday')).getByText('Drop to swap').parentElement!
     expect(target).toHaveTextContent('Drop to swapReplaces Pizza night')
@@ -1110,6 +1115,23 @@ describe.each([
     expect(puts(fetchMock)).toHaveLength(1)
   })
 
+  it('flips the floating copy to the left of and above the pointer where it would leave the viewport', async () => {
+    stubServer({ [`GET ${THIS_WEEK}`]: () => jsonResponse(200, planBody('draft')), ...dragLists })
+    await renderPage()
+    await screen.findByText('Pizza night')
+    const orzo = await quest('Lemon orzo')
+    vi.spyOn(orzo, 'getBoundingClientRect').mockReturnValue(DOMRect.fromRect({ x: 90, y: 90, width: 240, height: 60 }))
+
+    press(orzo)
+    const [x, y] = [window.innerWidth - 100, window.innerHeight - 40]
+    move(orzo, document.body, [x, y])
+    const copy = float()!
+    expect(copy.style.width).toBe('240px')
+    expect(copy.style.left).toBe(`${x - 48 - 240}px`)
+    expect(copy.style.top).toBe(`${y - 48 - 60}px`)
+    release(orzo)
+  })
+
   it('cancels a drag let go over no day, or cancelled, with no swap', async () => {
     const fetchMock = stubServer({ [`GET ${THIS_WEEK}`]: () => jsonResponse(200, planBody('draft')), ...dragLists })
     await renderPage()

web/src/plan/PlanPanel.module.css

@@ -208,8 +208,9 @@
   opacity: 0.55;
 }
 
-/* The dragged copy floating under the pointer: lifted with the large
+/* The dragged copy floating below right of the pointer: lifted with the
-   shadow and tilted -3deg. It lets the pointer through to the day under it. */
+   large shadow and tilted -3deg. It lets the pointer through to the day
+   under it. */
 .floating {
   position: fixed;
   z-index: 10;

web/src/plan/PlanPanel.tsx

@@ -60,7 +60,7 @@ function Grip() {
 // Draggable is a dinner of the panel or the strip, dragged onto a day to
 // swap it in: a button whose content is the row or the chip. While it is
 // dragged it is a dashed ghost, and with a pointer a copy of it floats
-// under the pointer, lifted and tilted.
+// below right of the pointer, lifted and tilted.
 function Draggable({
   dinner,
   fromQuestLog,

web/src/plan/drag.tsx

@@ -195,14 +195,32 @@ function dateAt(x: number, y: number): string | null {
 // not one.
 const DRAG_THRESHOLD = 4
 
-// Press is a pointer held on a draggable: its id, where it went down, how
+// The dragged copy floats this far below and to the right of the pointer,
-// far that was from the draggable's top left, and whether it has become a
+// as a drag image does, so it stays clear of the "Drop to swap" text
-// drag.
+// centred in the day the pointer is over. Where it would leave the viewport it flips to the
-type Press = { pointerId: number; x: number; y: number; dx: number; dy: number; width: number; dragging: boolean }
+// left of the pointer, or above it.
+const FLOAT_OFFSET = 48
+
+// Press is a pointer held on a draggable: its id, where it went down, the
+// draggable's size, and whether it has become a drag.
+type Press = { pointerId: number; x: number; y: number; width: number; height: number; dragging: boolean }
 
 // Float is where the dragged copy of a draggable is drawn, and how wide.
 export type Float = { left: number; top: number; width: number }
 
+// floatAt is where the dragged copy of the held draggable is drawn for the
+// pointer at (x, y): offset below right of it, flipped where that would
+// leave the viewport.
+function floatAt(held: Press, x: number, y: number): Float {
+  const right = x + FLOAT_OFFSET
+  const below = y + FLOAT_OFFSET
+  return {
+    left: right + held.width > window.innerWidth ? x - FLOAT_OFFSET - held.width : right,
+    top: below + held.height > window.innerHeight ? y - FLOAT_OFFSET - held.height : below,
+    width: held.width,
+  }
+}
+
 // useDraggable makes a panel row or a strip chip a draggable dinner. With a
 // pointer it is pressed, captured and moved past DRAG_THRESHOLD to pick it
 // up, its copy floats with the pointer, and letting go over a day drops it
@@ -243,9 +261,8 @@ export function useDraggable(pickup: Pickup) {
       pointerId: event.pointerId,
       x: event.clientX,
       y: event.clientY,
-      dx: event.clientX - rect.left,
-      dy: event.clientY - rect.top,
       width: rect.width,
+      height: rect.height,
       dragging: false,
     }
   }
@@ -261,7 +278,7 @@ export function useDraggable(pickup: Pickup) {
       }
       held.dragging = true
     }
-    setFloat({ left: event.clientX - held.dx, top: event.clientY - held.dy, width: held.width })
+    setFloat(floatAt(held, event.clientX, event.clientY))
     plan.over(dateAt(event.clientX, event.clientY))
   }