feat(preview): allow changing the preview placement

packages/react-dnd-preview/README.md

@@ -36,12 +36,12 @@ See also the [examples](examples/) for more information.
 import { usePreview } from 'react-dnd-preview'
 
 const MyPreview = () => {
-  const preview = usePreview()
+  const preview = usePreview({ placement: 'top', padding: {x: -20, y: 0 }})
   if (!preview.display) {
     return null
   }
-  const {itemType, item, style} = preview;
-  return <div className="item-list__item" style={style}>{itemType}</div>
+  const {itemType, item, style, ref} = preview;
+  return <div className="item-list__item" ref={ref} style={style}>{itemType}</div>
 }
 
 const App = () => {

packages/react-dnd-preview/examples/main/methods/common.tsx

@@ -11,9 +11,9 @@ export type GenPreviewProps = {
   method: string,
 }
 
-export const generatePreview = ({itemType, item, style}: PreviewProps, {row, col, title, method}: GenPreviewProps): JSX.Element => {
+export const generatePreview = ({itemType, item, style, ref}: PreviewProps, {row, col, title, method}: GenPreviewProps): JSX.Element => {
   return (
-    <Shape color={item.color} size={50} style={{
+    <Shape color={item.color} size={50} ref={ref} style={{
       ...style,
       top: `${row * 60}px`,
       left: `${col * 100}px`,

packages/react-dnd-preview/examples/offset/App.tsx

@@ -1,18 +1,21 @@
 import React, {CSSProperties, useState} from 'react'
 import {DndProvider} from 'react-dnd'
 import {TouchBackend} from 'react-dnd-touch-backend'
-import {usePreview} from '../../src'
+import {usePreview, Point} from '../../src'
+import type {PreviewPlacement} from '../../src/'
 import {Draggable, Shape, DragContent} from '../shared'
 
 type Kinds = 'default' | 'ref' | 'custom_client' | 'custom_source_client'
 
 type PreviewProps = {
   kind: Kinds,
   text: string,
+  placement?: PreviewPlacement,
+  padding?: Point
 }
 
-export const Preview = ({kind, text}: PreviewProps): JSX.Element | null => {
-  const preview = usePreview<DragContent, HTMLDivElement>()
+export const Preview = ({kind, text, placement, padding}: PreviewProps): JSX.Element | null => {
+  const preview = usePreview<DragContent, HTMLDivElement>({placement, padding})
   if (!preview.display) {
     return null
   }
@@ -47,23 +50,62 @@ export const Preview = ({kind, text}: PreviewProps): JSX.Element | null => {
 
 export const App = (): JSX.Element => {
   const [debug, setDebug] = useState(false)
+  const [previewPlacement, setPreviewPlacement] = useState<PreviewPlacement>('center')
+
+  const [paddingX, setPaddingX] = useState('0')
+  const [paddingY, setPaddingY] = useState('0')
+
+  const handlePlacementChange = (e: React.ChangeEvent<HTMLSelectElement>) => {
+    setPreviewPlacement(e.target.value as PreviewPlacement)
+  }
+
+  const handlePaddingXChange = (e: React.ChangeEvent<HTMLInputElement>) => {
+    setPaddingX(e.target.value)
+  }
+
+  const handlePaddingYChange = (e: React.ChangeEvent<HTMLInputElement>) => {
+    setPaddingY(e.target.value)
+  }
 
   return (
     <React.StrictMode>
+      <p>
+        <label htmlFor="previewPlacement">Preview placement: </label>
+        <select value={previewPlacement} id="previewPlacement" onChange={handlePlacementChange}>
+          <option value="center">center (default)</option>
+          <option value="top-start">top-start</option>
+          <option value="top">top</option>
+          <option value="top-end">top-end</option>
+          <option value="bottom-start">bottom-start</option>
+          <option value="bottom">bottom</option>
+          <option value="bottom-end">bottom-end</option>
+          <option value="left">left</option>
+          <option value="right">right</option>
+        </select>
+      </p>
+      <p>
+        <label htmlFor="previewPlacement">Padding x: </label>
+        <input type="text" value={paddingX} onChange={handlePaddingXChange}/>
+      </p>
+      <p>
+        <label htmlFor="previewPlacement">Padding y: </label>
+        <input type="text" value={paddingY} onChange={handlePaddingYChange}/>
+      </p>
       <p>
         <input type="checkbox" checked={debug} onChange={(e) => {
           setDebug(e.target.checked)
-        }} id="debug_mode" />
+        }} id="debug_mode"/>
         <label htmlFor="debug_mode">Debug mode</label>
+
       </p>
       <DndProvider backend={TouchBackend} options={{enableMouseEvents: true}}>
-        <Draggable />
-        <Preview text="default" kind="default" />
-        <Preview text="with ref" kind="ref" />
+        <Draggable/>
+        <Preview text="default" kind="default"/>
+        <Preview text="with ref" kind="ref" placement={previewPlacement} padding={{x: Number(paddingX), y: Number(paddingY)}}/>
         {debug ? (
           <>
-            <Preview text="custom ClientOffset" kind="custom_client" />
-            <Preview text="custom SourceClientOffset" kind="custom_source_client" />
+            <Preview text="custom ClientOffset" kind="custom_client"/>
+            <Preview text="custom SourceClientOffset" kind="custom_source_client"/>
           </>
         ) : null}
       </DndProvider>

packages/react-dnd-preview/src/Preview.tsx

@@ -1,17 +1,24 @@
 import React, {ReactNode} from 'react'
 import {usePreview} from './usePreview'
 import {Context, PreviewState} from './Context'
+import {PreviewPlacement, Point} from './offsets'
 
 export type PreviewGenerator<T = unknown, El extends Element = Element> = (state: PreviewState<T, El>) => JSX.Element
 
-export type PreviewProps<T = unknown, El extends Element = Element> = {
+export type PreviewProps<T = unknown, El extends Element = Element> = ({
   children: PreviewGenerator<T, El> | ReactNode
 } | {
   generator: PreviewGenerator<T, El>,
+}) & {
+    placement?: PreviewPlacement,
+    padding?: Point,
 }
 
 export const Preview = <T = unknown, El extends Element = Element>(props: PreviewProps<T, El>): JSX.Element | null => {
-  const result = usePreview<T, El>()
+  const result = usePreview<T, El>({
+    placement: props.placement,
+    padding: props.padding,
+  })
 
   if (!result.display) {
     return null

packages/react-dnd-preview/src/__tests__/usePreview.test.ts

@@ -3,6 +3,7 @@ import {renderHook, act} from '@testing-library/react'
 import {MockDragMonitor} from '@mocks/mocks'
 import {__setMockMonitor} from '@mocks/react-dnd'
 import {MutableRefObject} from 'react'
+import { PreviewPlacement } from '../offsets'
 
 describe('usePreview hook', () => {
   beforeEach(() => {
@@ -138,57 +139,92 @@ describe('usePreview hook', () => {
     })
   })
 
-  test('return true and data when DnD is in progress (with ref and parent offset)', async () => {
-    __setMockMonitor({
-      ...MockDragMonitor<{bluh: string}>({bluh: 'fake'}),
-      isDragging() {return true},
-      getItemType() {return 'no'},
-      getClientOffset() {return {x: 1, y: 2}},
-      getInitialClientOffset() {return {x: 1, y: 2}},
-      getInitialSourceClientOffset() {return {x: 0, y: 1}},
-    })
-    const {result, rerender} = renderHook(() => {return usePreview() as usePreviewStateFull})
-    const {current: {display, monitor: _monitor, ref, ...rest}} = result
-    expect(display).toBe(true)
-    expect(ref).not.toBeNull()
-    expect(rest).toEqual({
-      item: {bluh: 'fake'},
-      itemType: 'no',
-      style: {
-        pointerEvents: 'none',
-        position: 'fixed',
-        left: 0,
-        top: 0,
-        WebkitTransform: 'translate(0.0px, 1.0px)',
-        transform: 'translate(0.0px, 1.0px)',
-      },
-    })
-    await act<void>(() => {
-      // FIXME: not great...
-      (ref as MutableRefObject<HTMLDivElement>).current = {
-        ...document.createElement('div'),
-        getBoundingClientRect() {
-          return {
-            width: 100, height: 70,
-            x: 0, y: 0, bottom: 0, left: 0, right: 0, top: 0,
-            toJSON() { },
-          }
+  const cases: { placement?: PreviewPlacement, expectedTransform: string }[] = [
+    {
+      expectedTransform: 'translate(-49.0px, -33.0px)',
+    }, {
+      placement: 'center',
+      expectedTransform: 'translate(-49.0px, -33.0px)',
+    }, {
+      placement: 'top',
+      expectedTransform: 'translate(-49.0px, 2.0px)',
+    }, {
+      placement: 'top-start',
+      expectedTransform: 'translate(1.0px, 2.0px)',
+    }, {
+      placement: 'top-end',
+      expectedTransform: 'translate(-99.0px, 2.0px)',
+    }, {
+      placement: 'bottom',
+      expectedTransform: 'translate(-49.0px, -68.0px)',
+    }, {
+      placement: 'bottom-start',
+      expectedTransform: 'translate(1.0px, -68.0px)',
+    }, {
+      placement: 'bottom-end',
+      expectedTransform: 'translate(-99.0px, -68.0px)',
+    }, {
+      placement: 'left',
+      expectedTransform: 'translate(1.0px, -33.0px)',
+    }, {
+      placement: 'right',
+      expectedTransform: 'translate(-99.0px, -33.0px)',
+    }]
+
+  test.each(cases)(
+    'return true and data when DnD is in progress (with ref, parent offset and placement $placement)',
+    async ({placement, expectedTransform}) => {
+      __setMockMonitor({
+        ...MockDragMonitor<{bluh: string}>({bluh: 'fake'}),
+        isDragging() {return true},
+        getItemType() {return 'no'},
+        getClientOffset() {return {x: 1, y: 2}},
+        getInitialClientOffset() {return {x: 1, y: 2}},
+        getInitialSourceClientOffset() {return {x: 0, y: 1}},
+      })
+      const {result, rerender} = renderHook(() => {return usePreview({ placement }) as usePreviewStateFull})
+      const {current: {display, monitor: _monitor, ref, ...rest}} = result
+      expect(display).toBe(true)
+      expect(ref).not.toBeNull()
+      expect(rest).toEqual({
+        item: {bluh: 'fake'},
+        itemType: 'no',
+        style: {
+          pointerEvents: 'none',
+          position: 'fixed',
+          left: 0,
+          top: 0,
+          WebkitTransform: 'translate(0.0px, 1.0px)',
+          transform: 'translate(0.0px, 1.0px)',
         },
-      }
-    })
-    rerender()
-    const {current: {display: _display, monitor: _monitor2, ref: _ref, ...rest2}} = result
-    expect(rest2).toEqual({
-      item: {bluh: 'fake'},
-      itemType: 'no',
-      style: {
-        pointerEvents: 'none',
-        position: 'fixed',
-        left: 0,
-        top: 0,
-        WebkitTransform: 'translate(-49.0px, -33.0px)',
-        transform: 'translate(-49.0px, -33.0px)',
-      },
-    })
-  })
+      })
+      await act<void>(() => {
+        // FIXME: not great...
+        (ref as MutableRefObject<HTMLDivElement>).current = {
+          ...document.createElement('div'),
+          getBoundingClientRect() {
+            return {
+              width: 100, height: 70,
+              x: 0, y: 0, bottom: 0, left: 0, right: 0, top: 0,
+              toJSON() { },
+            }
+          },
+        }
+      })
+      rerender({ placement })
+      const {current: {display: _display, monitor: _monitor2, ref: _ref, ...rest2}} = result
+      expect(rest2).toEqual({
+        item: {bluh: 'fake'},
+        itemType: 'no',
+        style: {
+          pointerEvents: 'none',
+          position: 'fixed',
+          left: 0,
+          top: 0,
+          WebkitTransform: expectedTransform,
+          transform: expectedTransform,
+        },
+      })
+    }
+  )
 })

packages/react-dnd-preview/src/index.ts

@@ -1,6 +1,7 @@
 export { Preview } from './Preview'
 export type { PreviewProps, PreviewGenerator } from './Preview'
 export { usePreview } from './usePreview'
+export type { PreviewPlacement, Point } from './offsets'
 export type { usePreviewState, usePreviewStateContent } from './usePreview'
 export { Context } from './Context'
 export type { PreviewState } from './Context'

packages/react-dnd-preview/src/offsets.ts

@@ -14,13 +14,31 @@ export type Point = {
   y: number,
 }
 
+export type PreviewPlacement =
+    | 'center'
+    | 'top'
+    | 'top-start'
+    | 'top-end'
+    | 'bottom'
+    | 'bottom-start'
+    | 'bottom-end'
+    | 'left'
+    | 'right'
+
 const subtract = (a: Point, b: Point): Point => {
   return {
     x: a.x - b.x,
     y: a.y - b.y,
   }
 }
 
+const add = (a: Point, b: Point): Point => {
+  return {
+    x: a.x + b.x,
+    y: a.y + b.y,
+  }
+}
+
 const calculateParentOffset = (monitor: DragLayerMonitor): Point => {
   const client = monitor.getInitialClientOffset()
   const source = monitor.getInitialSourceClientOffset()
@@ -30,7 +48,42 @@ const calculateParentOffset = (monitor: DragLayerMonitor): Point => {
   return subtract(client, source)
 }
 
-export const calculatePointerPosition = (monitor: DragLayerMonitor, childRef: RefObject<Element>): Point | null => {
+const calculateXOffset = (placement: PreviewPlacement, bb: DOMRect): number => {
+  switch (placement) {
+  case 'left':
+  case 'top-start':
+  case 'bottom-start':
+    return 0
+  case 'right':
+  case 'top-end':
+  case 'bottom-end':
+    return bb.width
+  default:
+    return bb.width / 2
+  }
+}
+
+const calculateYOffset = (placement: PreviewPlacement, bb: DOMRect): number => {
+  switch (placement) {
+  case 'top':
+  case 'top-start':
+  case 'top-end':
+    return 0
+  case 'bottom':
+  case 'bottom-start':
+  case 'bottom-end':
+    return bb.height
+  default:
+    return bb.height / 2
+  }
+}
+
+export const calculatePointerPosition = (
+  monitor: DragLayerMonitor,
+  childRef: RefObject<Element>,
+  placement: PreviewPlacement = 'center',
+  padding: Point = { x: 0, y: 0 },
+): Point | null => {
   const offset = monitor.getClientOffset()
   if (offset === null) {
     return null
@@ -43,6 +96,7 @@ export const calculatePointerPosition = (monitor: DragLayerMonitor, childRef: Re
   }
 
   const bb = childRef.current.getBoundingClientRect()
-  const middle = {x: bb.width / 2, y: bb.height / 2}
-  return subtract(offset, middle)
+  const previewOffset = { x: calculateXOffset(placement, bb), y: calculateYOffset(placement, bb) }
+
+  return add(subtract(offset, previewOffset), padding)
 }