Initial marker features

- Add comments about cursor lock, framestamp lock
- Add PointableSet, Mark Ids, dataverse usage fix
- Add marker dragging, fix PointerCapturing

Co-authored-by: Cole Lawrence <cole@colelawrence.com>
Co-authored-by: Aria <aria.minaei@gmail.com>

theatre/core/src/projects/store/types/SheetState_Historic.ts

@@ -28,6 +28,7 @@ export type HistoricPositionalSequence = {
   type: 'PositionalSequence'
   length: number
   /**
+   * Given the most common case of tracking a sequence against time (where 1 second = position 1),
    * If set to, say, 30, then the keyframe editor will try to snap all keyframes
    * to a 30fps grid
    */

theatre/shared/src/utils/PointableSet.ts

@@ -0,0 +1,94 @@
+import type {StrictRecord} from './types'
+
+/**
+ * Consistent way to maintain an unordered structure which plays well with dataverse pointers and
+ * data change tracking:
+ * - paths to items are stable;
+ * - changing one item does not change `allIds`, so it can be mapped over in React without
+ *   unnecessary re-renders
+ */
+export type PointableSet<Id extends string, V> = {
+  /**
+   * Usually accessed through pointers before accessing the actual value, so we can separate
+   * changes to individual items from changes to the entire list of items.
+   */
+  byId: StrictRecord<Id, V>
+  /**
+   * Separate list of ids allows us to recognize changes to set item memberships, without being triggered changed when
+   * the contents of its items have changed.
+   */
+  allIds: StrictRecord<Id, true>
+}
+
+export const pointableSetUtil = {
+  create<Id extends string, V>(
+    values?: Iterable<[Id, V]>,
+  ): PointableSet<Id, V> {
+    const set: PointableSet<Id, V> = {byId: {}, allIds: {}}
+    if (values) {
+      for (const [id, value] of values) {
+        set.byId[id] = value
+        set.allIds[id] = true
+      }
+    }
+    return set
+  },
+  shallowCopy<Id extends string, V>(
+    existing: PointableSet<Id, V> | undefined,
+  ): PointableSet<Id, V> {
+    return {
+      byId: {...existing?.byId},
+      allIds: {...existing?.allIds},
+    }
+  },
+  add<Id extends string, V>(
+    existing: PointableSet<Id, V> | undefined,
+    id: Id,
+    value: V,
+  ): PointableSet<Id, V> {
+    return {
+      byId: {...existing?.byId, [id]: value},
+      allIds: {...existing?.allIds, [id]: true},
+    }
+  },
+  merge<Id extends string, V>(
+    sets: PointableSet<Id, V>[],
+  ): PointableSet<Id, V> {
+    const target = pointableSetUtil.create<Id, V>()
+    for (let i = 0; i < sets.length; i++) {
+      target.byId = {...target.byId, ...sets[i].byId}
+      target.allIds = {...target.allIds, ...sets[i].allIds}
+    }
+    return target
+  },
+  remove<Id extends string, V>(
+    existing: PointableSet<Id, V>,
+    id: Id,
+  ): PointableSet<Id, V> {
+    const set = pointableSetUtil.shallowCopy(existing)
+    delete set.allIds[id]
+    delete set.byId[id]
+    return set
+  },
+  /**
+   * Note: this is not very performant (it's not crazy slow or anything)
+   * it's just that it's not able to re-use object classes in v8 due to
+   * excessive `delete obj[key]` instances.
+   *
+   * `Map`s would be faster, but they aren't used for synchronized JSON state stuff.
+   * See {@link StrictRecord} for related conversation.
+   */
+  filter<Id extends string, V>(
+    existing: PointableSet<Id, V>,
+    predicate: (value: V | undefined) => boolean | undefined | null,
+  ): PointableSet<Id, V> {
+    const set = pointableSetUtil.shallowCopy(existing)
+    for (const [id, value] of Object.entries(set.byId)) {
+      if (!predicate(value)) {
+        delete set.allIds[id]
+        delete set.byId[id]
+      }
+    }
+    return set
+  },
+}

theatre/shared/src/utils/ids.ts

@@ -1,6 +1,5 @@
 import {nanoid as generateNonSecure} from 'nanoid/non-secure'
 import type {Nominal} from './Nominal'
-import type {$IntentionalAny} from './types'
 
 export type KeyframeId = Nominal<'KeyframeId'>
 
@@ -9,7 +8,7 @@ export function generateKeyframeId(): KeyframeId {
 }
 
 export function asKeyframeId(s: string): KeyframeId {
-  return s as $IntentionalAny
+  return s as KeyframeId
 }
 
 export type ProjectId = Nominal<'ProjectId'>
@@ -17,14 +16,19 @@ export type SheetId = Nominal<'SheetId'>
 export type SheetInstanceId = Nominal<'SheetInstanceId'>
 export type PaneInstanceId = Nominal<'PaneInstanceId'>
 export type SequenceTrackId = Nominal<'SequenceTrackId'>
+export type SequenceMarkerId = Nominal<'SequenceMarkerId'>
 export type ObjectAddressKey = Nominal<'ObjectAddressKey'>
 /** UI panels can contain a {@link PaneInstanceId} or something else. */
 export type UIPanelId = Nominal<'UIPanelId'>
 
 export function generateSequenceTrackId(): SequenceTrackId {
-  return generateNonSecure(10) as $IntentionalAny as SequenceTrackId
+  return generateNonSecure(10) as SequenceTrackId
 }
 
 export function asSequenceTrackId(s: string): SequenceTrackId {
-  return s as $IntentionalAny
+  return s as SequenceTrackId
+}
+
+export function generateSequenceMarkerId(): SequenceMarkerId {
+  return generateNonSecure(10) as SequenceMarkerId
 }

theatre/shared/src/utils/types.ts

@@ -68,7 +68,8 @@ export type DeepPartialOfSerializableValue<T extends SerializableValue> =
  * This is equivalent to `Partial<Record<Key, V>>` being used to describe a sort of Map
  * where the keys might not have values.
  *
- * We do not use `Map`s, because they add comlpexity with converting to `JSON.stringify` + pointer types
+ * We do not use `Map`s or `Set`s, because they add complexity with converting to
+ * `JSON.stringify` + pointer types.
  */
 export type StrictRecord<Key extends string, V> = {[K in Key]?: V}
 

theatre/studio/src/UIRoot/PointerCapturing.tsx

@@ -1,9 +1,11 @@
-import React, {useContext, useMemo} from 'react'
+import React, {useContext, useEffect, useMemo} from 'react'
 import type {$IntentionalAny} from '@theatre/shared/utils/types'
 
 /** See {@link PointerCapturing} */
 export type CapturedPointer = {
   release(): void
+  /** Double check that you still have the current capture and weren't forcibly released */
+  isCapturing(): boolean
 }
 
 /**
@@ -23,41 +25,73 @@ export type PointerCapturing = {
   capturePointer(debugReason: string): CapturedPointer
 }
 
-type PointerCapturingFn = (forDebugName: string) => PointerCapturing
+type InternalPointerCapturing = {
+  capturing: PointerCapturing
+  forceRelease(): void
+}
+
+type PointerCapturingFn = (forDebugName: string) => InternalPointerCapturing
+
+// const logger = console
 
 function _usePointerCapturingContext(): PointerCapturingFn {
-  let [currentCapture, setCurrentCapture] = React.useState<null | {
+  type CaptureInfo = {
     debugOwnerName: string
     debugReason: string
-  }>(null)
+  }
+  let currentCaptureRef = React.useRef<null | CaptureInfo>(null)
 
   return (forDebugName) => {
-    return {
+    /** keep track of the captures being made by this user of {@link usePointerCapturing} */
+    let localCapture: CaptureInfo | null
+    const updateCapture = (to: CaptureInfo | null): CaptureInfo | null => {
+      localCapture = to
+      currentCaptureRef.current = to
+      return to
+    }
+    const capturing: PointerCapturing = {
       capturePointer(reason) {
         // logger.log('Capturing pointer', {forDebugName, reason})
-        if (currentCapture != null) {
+        if (currentCaptureRef.current != null) {
           throw new Error(
-            `"${forDebugName}" attempted capturing pointer for "${reason}" while already captured by "${currentCapture.debugOwnerName}" for "${currentCapture.debugReason}"`,
+            `"${forDebugName}" attempted capturing pointer for "${reason}" while already captured by "${currentCaptureRef.current.debugOwnerName}" for "${currentCaptureRef.current.debugReason}"`,
           )
         }
 
-        setCurrentCapture({debugOwnerName: forDebugName, debugReason: reason})
+        const releaseCapture = updateCapture({
+          debugOwnerName: forDebugName,
+          debugReason: reason,
+        })
 
-        const releaseCapture = currentCapture
         return {
+          isCapturing() {
+            return releaseCapture === currentCaptureRef.current
+          },
           release() {
-            if (releaseCapture === currentCapture) {
+            if (releaseCapture === currentCaptureRef.current) {
               // logger.log('Releasing pointer', {
               //   forDebugName,
               //   reason,
               // })
-              setCurrentCapture(null)
+              updateCapture(null)
+              return true
             }
+            return false
           },
         }
       },
       isPointerBeingCaptured() {
-        return currentCapture != null
+        return currentCaptureRef.current != null
+      },
+    }
+
+    return {
+      capturing,
+      forceRelease() {
+        if (currentCaptureRef.current === localCapture) {
+          // logger.log('Force releasing pointer', currentCaptureRef.current)
+          updateCapture(null)
+        }
       },
     }
   }
@@ -96,7 +130,16 @@ export function ProvidePointerCapturing(props: {
 
 export function usePointerCapturing(forDebugName: string): PointerCapturing {
   const pointerCapturingFn = useContext(PointerCapturingContext)
-  return useMemo(() => {
+  const control = useMemo(() => {
     return pointerCapturingFn(forDebugName)
   }, [forDebugName, pointerCapturingFn])
+
+  useEffect(() => {
+    return () => {
+      // force release on unmount
+      control.forceRelease()
+    }
+  }, [forDebugName, pointerCapturingFn])
+
+  return control.capturing
 }

theatre/studio/src/css.ts

@@ -1,6 +1,13 @@
 import {lighten} from 'polished'
 import {css} from 'styled-components'
 
+/**
+ * This CSS string is used to correctly set pointer-events on an element
+ * when the pointer is dragging something.
+ * Naming explanation: "NormalMode" as opposed to dragging mode.
+ *
+ * @see PointerEventsHandler - the place that sets `.normal` on #pointer-root
+ */
 export const pointerEventsAutoInNormalMode = css`
   #pointer-root & {
     pointer-events: none;

theatre/studio/src/panels/SequenceEditorPanel/DopeSheet/Right/BasicKeyframedTrack/KeyframeEditor/KeyframeDot.tsx

@@ -11,12 +11,12 @@ import type {UseDragOpts} from '@theatre/studio/uiComponents/useDrag'
 import useRefAndState from '@theatre/studio/utils/useRefAndState'
 import {val} from '@theatre/dataverse'
 import {lighten} from 'polished'
-import React, {useMemo, useRef, useState} from 'react'
+import React, {useMemo, useRef} from 'react'
 import styled from 'styled-components'
 import {useLockFrameStampPosition} from '@theatre/studio/panels/SequenceEditorPanel/FrameStampPositionProvider'
 import {attributeNameThatLocksFramestamp} from '@theatre/studio/panels/SequenceEditorPanel/FrameStampPositionProvider'
 import {
-  lockedCursorCssPropName,
+  lockedCursorCssVarName,
   useCssCursorLock,
 } from '@theatre/studio/uiComponents/PointerEventsHandler'
 import SnapCursor from './SnapCursor.svg'
@@ -42,7 +42,8 @@ const dotTheme = {
   },
 }
 
-const Square = styled.div<{isSelected: boolean}>`
+/** The keyframe diamond ◆ */
+const Diamond = styled.div<{isSelected: boolean}>`
   position: absolute;
   ${dims(DOT_SIZE_PX)}
 
@@ -65,8 +66,11 @@ const HitZone = styled.div`
 
   #pointer-root.draggingPositionInSequenceEditor & {
     pointer-events: auto;
-    cursor: var(${lockedCursorCssPropName});
+    cursor: var(${lockedCursorCssVarName});
 
+    // ⸢⸤⸣⸥ thing
+    // This box extends the hitzone so the user does not
+    // accidentally leave the hitzone
     &:hover:after {
       position: absolute;
       top: calc(50% - ${SNAP_CURSOR_SIZE_PX / 2}px);
@@ -84,7 +88,7 @@ const HitZone = styled.div`
     pointer-events: none !important;
   }
 
-  &:hover + ${Square}, &.beingDragged + ${Square} {
+  &:hover + ${Diamond}, &.beingDragged + ${Diamond} {
     ${dims(DOT_HOVER_SIZE_PX)}
   }
 `
@@ -109,7 +113,7 @@ const KeyframeDot: React.VFC<IKeyframeDotProps> = (props) => {
         }}
         className={isDragging ? 'beingDragged' : ''}
       />
-      <Square isSelected={!!props.selection} />
+      <Diamond isSelected={!!props.selection} />
       {contextMenu}
     </>
   )
@@ -142,9 +146,6 @@ function useDragKeyframe(
   node: HTMLDivElement | null,
   props: IKeyframeDotProps,
 ): [isDragging: boolean] {
-  const [isDragging, setIsDragging] = useState(false)
-  useLockFrameStampPosition(isDragging, props.keyframe.position)
-
   const propsRef = useRef(props)
   propsRef.current = props
 
@@ -158,10 +159,9 @@ function useDragKeyframe(
       | undefined
 
     return {
-      debugName: 'Dot/useDragKeyframe',
+      debugName: 'KeyframeDot/useDragKeyframe',
 
       onDragStart(event) {
-        setIsDragging(true)
         const props = propsRef.current
         if (props.selection) {
           const {selection, leaf} = props
@@ -229,29 +229,21 @@ function useDragKeyframe(
         })
       },
       onDragEnd(dragHappened) {
-        setIsDragging(false)
-
         if (selectionDragHandlers) {
           selectionDragHandlers.onDragEnd?.(dragHappened)
 
           selectionDragHandlers = undefined
         }
-        if (dragHappened) {
+        if (dragHappened) tempTransaction?.commit()
-          if (tempTransaction) {
+        else tempTransaction?.discard()
-            tempTransaction.commit()
-          }
-        } else {
-          if (tempTransaction) {
-            tempTransaction.discard()
-          }
-        }
         tempTransaction = undefined
       },
     }
   }, [])
 
-  useDrag(node, useDragOpts)
+  const [isDragging] = useDrag(node, useDragOpts)
 
+  useLockFrameStampPosition(isDragging, props.keyframe.position)
   useCssCursorLock(isDragging, 'draggingPositionInSequenceEditor', 'ew-resize')
 
   return [isDragging]

theatre/studio/src/panels/SequenceEditorPanel/FrameStampPositionProvider.tsx

@@ -40,6 +40,12 @@ type LockItem = {
 
 let lastLockId = 0
 
+/**
+ * Provides snapping positions to "stamps".
+ *
+ * One example of a stamp includes the "Keyframe Dot" which show a `⌜⌞⌝⌟` kinda UI
+ * around the dot when dragged over.
+ */
 const FrameStampPositionProvider: React.FC<{
   layoutP: Pointer<SequenceEditorPanelLayout>
 }> = ({children, layoutP}) => {
@@ -144,6 +150,13 @@ export const useLockFrameStampPosition = (shouldLock: boolean, val: number) => {
  * Elements that need this behavior must set a data attribute like so:
  * <div data-theatre-lock-framestamp-to="120.55" />
  * Setting this attribute to "hide" hides the stamp.
+ *
+ * @see lockedCursorCssVarName - CSS variable used to set the cursor on an element that
+ * should lock the framestamp. Look for usages.
+ * @see pointerEventsAutoInNormalMode - CSS snippet used to correctly set
+ * `pointer-events` on an element that should lock the framestamp.
+ *
+ * See {@link FrameStampPositionProvider}
  */
 export const attributeNameThatLocksFramestamp =
   'data-theatre-lock-framestamp-to'

theatre/studio/src/panels/SequenceEditorPanel/GraphEditor/BasicKeyframedTrack/KeyframeEditor/GraphEditorDotNonScalar.tsx

@@ -14,7 +14,7 @@ import {useLockFrameStampPosition} from '@theatre/studio/panels/SequenceEditorPa
 import {attributeNameThatLocksFramestamp} from '@theatre/studio/panels/SequenceEditorPanel/FrameStampPositionProvider'
 import {pointerEventsAutoInNormalMode} from '@theatre/studio/css'
 import {
-  lockedCursorCssPropName,
+  lockedCursorCssVarName,
   useCssCursorLock,
 } from '@theatre/studio/uiComponents/PointerEventsHandler'
 
@@ -45,7 +45,7 @@ const HitZone = styled.circle`
 
   #pointer-root.draggingPositionInSequenceEditor & {
     pointer-events: auto;
-    cursor: var(${lockedCursorCssPropName});
+    cursor: var(${lockedCursorCssVarName});
   }
 
   &.beingDragged {

theatre/studio/src/panels/SequenceEditorPanel/GraphEditor/BasicKeyframedTrack/KeyframeEditor/GraphEditorDotScalar.tsx

@@ -14,7 +14,7 @@ import {useLockFrameStampPosition} from '@theatre/studio/panels/SequenceEditorPa
 import {attributeNameThatLocksFramestamp} from '@theatre/studio/panels/SequenceEditorPanel/FrameStampPositionProvider'
 import {pointerEventsAutoInNormalMode} from '@theatre/studio/css'
 import {
-  lockedCursorCssPropName,
+  lockedCursorCssVarName,
   useCssCursorLock,
 } from '@theatre/studio/uiComponents/PointerEventsHandler'
 
@@ -45,7 +45,7 @@ const HitZone = styled.circle`
 
   #pointer-root.draggingPositionInSequenceEditor & {
     pointer-events: auto;
-    cursor: var(${lockedCursorCssPropName});
+    cursor: var(${lockedCursorCssVarName});
   }
 
   &.beingDragged {

theatre/studio/src/panels/SequenceEditorPanel/RightOverlay/FocusRangeZone/FocusRangeThumb.tsx

@@ -10,7 +10,7 @@ import {
 } from '@theatre/studio/panels/SequenceEditorPanel/RightOverlay/TopStrip'
 import type {CommitOrDiscard} from '@theatre/studio/StudioStore/StudioStore'
 import {
-  lockedCursorCssPropName,
+  lockedCursorCssVarName,
   useCssCursorLock,
 } from '@theatre/studio/uiComponents/PointerEventsHandler'
 import useDrag from '@theatre/studio/uiComponents/useDrag'
@@ -57,7 +57,7 @@ const TheDiv = styled.div<{enabled: boolean; type: 'start' | 'end'}>`
 
   #pointer-root.draggingPositionInSequenceEditor & {
     pointer-events: auto;
-    cursor: var(${lockedCursorCssPropName});
+    cursor: var(${lockedCursorCssVarName});
   }
 
   &.dragging {

theatre/studio/src/panels/SequenceEditorPanel/RightOverlay/MarkerDot.tsx

@@ -0,0 +1,305 @@
+import type {Pointer} from '@theatre/dataverse'
+import {val} from '@theatre/dataverse'
+import {useVal} from '@theatre/react'
+import {pointerEventsAutoInNormalMode} from '@theatre/studio/css'
+import getStudio from '@theatre/studio/getStudio'
+import {
+  lockedCursorCssVarName,
+  useCssCursorLock,
+} from '@theatre/studio/uiComponents/PointerEventsHandler'
+import useContextMenu from '@theatre/studio/uiComponents/simpleContextMenu/useContextMenu'
+import useRefAndState from '@theatre/studio/utils/useRefAndState'
+import React, {useMemo, useRef} from 'react'
+import styled from 'styled-components'
+import {
+  attributeNameThatLocksFramestamp,
+  useLockFrameStampPosition,
+} from '@theatre/studio/panels/SequenceEditorPanel/FrameStampPositionProvider'
+import type {SequenceEditorPanelLayout} from '@theatre/studio/panels/SequenceEditorPanel/layout/layout'
+import type {SequenceMarkerId} from '@theatre/shared/utils/ids'
+import type {SheetAddress} from '@theatre/shared/utils/addresses'
+import SnapCursor from './SnapCursor.svg'
+import MarkerDotVisual from './MarkerDotVisual.svg'
+import useDrag from '@theatre/studio/uiComponents/useDrag'
+import type {UseDragOpts} from '@theatre/studio/uiComponents/useDrag'
+import type {CommitOrDiscard} from '@theatre/studio/StudioStore/StudioStore'
+import type {StudioHistoricStateSequenceEditorMarker} from '@theatre/studio/store/types'
+import {zIndexes} from '@theatre/studio/panels/SequenceEditorPanel/SequenceEditorPanel'
+
+const MARKER_SIZE_W_PX = 10
+const MARKER_SIZE_H_PX = 8
+const HIT_ZONE_SIZE_PX = 12
+const SNAP_CURSOR_SIZE_PX = 34
+const MARKER_HOVER_SIZE_W_PX = MARKER_SIZE_W_PX * 2
+const MARKER_HOVER_SIZE_H_PX = MARKER_SIZE_H_PX * 2
+const dims = (w: number, h = w) => `
+  left: ${w * -0.5}px;
+  top: ${h * -0.5}px;
+  width: ${w}px;
+  height: ${h}px;
+`
+
+const MarkerVisualDot = styled.div`
+  position: absolute;
+  ${dims(MARKER_SIZE_W_PX, MARKER_SIZE_H_PX)}
+
+  background-image: url(${MarkerDotVisual});
+  background-size: contain;
+  pointer-events: none;
+`
+
+const HitZone = styled.div`
+  position: absolute;
+  ${dims(HIT_ZONE_SIZE_PX)};
+  z-index: 1;
+
+  cursor: ew-resize;
+
+  ${pointerEventsAutoInNormalMode};
+
+  // "All instances of this component <Mark/> inside #pointer-root when it has the .draggingPositionInSequenceEditor class"
+  // ref: https://styled-components.com/docs/basics#pseudoelements-pseudoselectors-and-nesting
+  #pointer-root.draggingPositionInSequenceEditor:not(.draggingMarker) &,
+  #pointer-root.draggingPositionInSequenceEditor &.beingDragged {
+    pointer-events: auto;
+    cursor: var(${lockedCursorCssVarName});
+  }
+
+  #pointer-root.draggingPositionInSequenceEditor:not(.draggingMarker) & {
+    pointer-events: auto;
+    cursor: var(${lockedCursorCssVarName});
+
+    // ⸢⸤⸣⸥ thing
+    // This box extends the hitzone so the user does not
+    // accidentally leave the hitzone
+    &:hover:after {
+      position: absolute;
+      top: calc(50% - ${SNAP_CURSOR_SIZE_PX / 2}px);
+      left: calc(50% - ${SNAP_CURSOR_SIZE_PX / 2}px);
+      width: ${SNAP_CURSOR_SIZE_PX}px;
+      height: ${SNAP_CURSOR_SIZE_PX}px;
+      display: block;
+      content: ' ';
+      background: url(${SnapCursor}) no-repeat 100% 100%;
+      // This icon might also fit: GiConvergenceTarget
+    }
+  }
+
+  &.beingDragged {
+    pointer-events: none !important;
+  }
+
+  &:hover + ${MarkerVisualDot}, &.beingDragged + ${MarkerVisualDot} {
+    ${dims(MARKER_HOVER_SIZE_W_PX, MARKER_HOVER_SIZE_H_PX)}
+  }
+`
+type IMarkerDotProps = {
+  layoutP: Pointer<SequenceEditorPanelLayout>
+  markerId: SequenceMarkerId
+}
+
+const MarkerDot: React.VFC<IMarkerDotProps> = ({layoutP, markerId}) => {
+  const sheetAddress = useVal(layoutP.sheet.address)
+  const marker = useVal(
+    getStudio().atomP.historic.projects.stateByProjectId[sheetAddress.projectId]
+      .stateBySheetId[sheetAddress.sheetId].sequenceEditor.markerSet.byId[
+      markerId
+    ],
+  )
+  if (!marker) {
+    // 1/10 maybe this is normal if React tries to re-render this with
+    // out of date data. (e.g. Suspense / Transition stuff?)
+    return null
+  }
+
+  return <MarkerDotDefined marker={marker} layoutP={layoutP} />
+}
+
+export default MarkerDot
+
+type IMarkerDotDefinedProps = {
+  layoutP: Pointer<SequenceEditorPanelLayout>
+  marker: StudioHistoricStateSequenceEditorMarker
+}
+
+const MarkerDotDefined: React.VFC<IMarkerDotDefinedProps> = ({
+  layoutP,
+  marker,
+}) => {
+  const sheetAddress = useVal(layoutP.sheet.address)
+  const clippedSpaceFromUnitSpace = useVal(layoutP.clippedSpace.fromUnitSpace)
+
+  const [markRef, markNode] = useRefAndState<HTMLDivElement | null>(null)
+
+  const [contextMenu] = useMarkerContextMenu(markNode, {
+    sheetAddress,
+    markerId: marker.id,
+  })
+
+  const [isDragging] = useDragMarker(markNode, {
+    layoutP,
+    marker,
+  })
+
+  return (
+    <div
+      style={{
+        position: 'absolute',
+        zIndex: zIndexes.marker,
+        transform: `translateX(${clippedSpaceFromUnitSpace(
+          marker.position,
+        )}px)`,
+        // below the sequence ruler "top bar"
+        top: '18px',
+      }}
+    >
+      {contextMenu}
+      <HitZone
+        ref={markRef}
+        // `data-pos` and `attributeNameThatLocksFramestamp` are used by FrameStampPositionProvider
+        // in order to handle snapping the playhead. Adding these props effectively
+        // causes the playhead to "snap" to the marker on mouse over.
+        // `pointerEventsAutoInNormalMode` and `lockedCursorCssVarName` in the CSS above are also
+        // used to make this behave correctly.
+        {...{
+          [attributeNameThatLocksFramestamp]: marker.position.toFixed(3),
+          [POSITION_SNAPPING.attributeNameForPosition]:
+            marker.position.toFixed(3),
+        }}
+        className={isDragging ? 'beingDragged' : ''}
+      />
+      <MarkerVisualDot />
+    </div>
+  )
+}
+
+function useMarkerContextMenu(
+  node: HTMLElement | null,
+  options: {
+    sheetAddress: SheetAddress
+    markerId: SequenceMarkerId
+  },
+) {
+  return useContextMenu(node, {
+    menuItems() {
+      return [
+        {
+          label: 'Remove marker',
+          callback: () => {
+            getStudio().transaction(({stateEditors}) => {
+              stateEditors.studio.historic.projects.stateByProjectId.stateBySheetId.sequenceEditor.removeMarker(
+                {
+                  sheetAddress: options.sheetAddress,
+                  markerId: options.markerId,
+                },
+              )
+            })
+          },
+        },
+      ]
+    },
+  })
+}
+
+function useDragMarker(
+  node: HTMLDivElement | null,
+  props: {
+    layoutP: Pointer<SequenceEditorPanelLayout>
+    marker: StudioHistoricStateSequenceEditorMarker
+  },
+): [isDragging: boolean] {
+  const propsRef = useRef(props)
+  propsRef.current = props
+
+  const useDragOpts = useMemo<UseDragOpts>(() => {
+    let toUnitSpace: SequenceEditorPanelLayout['scaledSpace']['toUnitSpace']
+    let tempTransaction: CommitOrDiscard | undefined
+    let markerAtStartOfDrag: StudioHistoricStateSequenceEditorMarker
+
+    return {
+      debugName: `MarkerDot/useDragMarker (${props.marker.id})`,
+
+      onDragStart(_event) {
+        markerAtStartOfDrag = propsRef.current.marker
+        toUnitSpace = val(props.layoutP.scaledSpace.toUnitSpace)
+      },
+      onDrag(dx, _dy, event) {
+        const original = markerAtStartOfDrag
+        const newPosition = Math.max(
+          // check if our event hoversover a [data-pos] element
+          POSITION_SNAPPING.checkIfMouseEventSnapToPos(event, {
+            ignore: node,
+          }) ??
+            // if we don't find snapping target, check the distance dragged + original position
+            original.position + toUnitSpace(dx),
+          // sanitize to minimum of zero
+          0,
+        )
+
+        tempTransaction?.discard()
+        tempTransaction = getStudio()!.tempTransaction(({stateEditors}) => {
+          stateEditors.studio.historic.projects.stateByProjectId.stateBySheetId.sequenceEditor.replaceMarkers(
+            {
+              sheetAddress: val(props.layoutP.sheet.address),
+              markers: [{...original, position: newPosition}],
+              snappingFunction: val(props.layoutP.sheet).getSequence()
+                .closestGridPosition,
+            },
+          )
+        })
+      },
+      onDragEnd(dragHappened) {
+        if (dragHappened) tempTransaction?.commit()
+        else tempTransaction?.discard()
+        tempTransaction = undefined
+      },
+    }
+  }, [])
+
+  const [isDragging] = useDrag(node, useDragOpts)
+
+  useLockFrameStampPosition(isDragging, props.marker.position)
+  useCssCursorLock(
+    isDragging,
+    'draggingPositionInSequenceEditor draggingMarker',
+    'ew-resize',
+  )
+
+  return [isDragging]
+}
+
+// Pretty much same code as for keyframe and similar for playhead.
+// Consider if we should unify the implementations.
+// - See "useLockFrameStampPosition"
+// - Also see "pointerPositionInUnitSpace" for a related impl (for different problem)
+const POSITION_SNAPPING = {
+  /**
+   * Used to indicate that when hovering over this element, we should enable
+   * snapping to the given position.
+   */
+  attributeNameForPosition: 'data-pos',
+  checkIfMouseEventSnapToPos(
+    event: MouseEvent,
+    options?: {ignore?: HTMLElement | null},
+  ): number | null {
+    const snapTarget = event
+      .composedPath()
+      .find(
+        (el): el is Element =>
+          el instanceof Element &&
+          el !== options?.ignore &&
+          el.hasAttribute(POSITION_SNAPPING.attributeNameForPosition),
+      )
+
+    if (snapTarget) {
+      const snapPos = parseFloat(
+        snapTarget.getAttribute(POSITION_SNAPPING.attributeNameForPosition)!,
+      )
+      if (isFinite(snapPos)) {
+        return snapPos
+      }
+    }
+
+    return null
+  },
+}

theatre/studio/src/panels/SequenceEditorPanel/RightOverlay/MarkerDotVisual.svg

@@ -0,0 +1,9 @@
+<svg width="10" height="8" viewBox="0 0 10 8" fill="none" xmlns="http://www.w3.org/2000/svg">
+<mask id="mask0_220_60402" style="mask-type:alpha" maskUnits="userSpaceOnUse" x="0" y="3" width="10" height="6">
+<rect width="8.56043" height="5.43915" transform="matrix(-1 -8.74228e-08 -8.74228e-08 1 9.28027 3.28027)" fill="#C4C4C4"/>
+</mask>
+<g mask="url(#mask0_220_60402)">
+<rect width="6" height="6" transform="matrix(-0.707107 -0.707107 -0.707107 0.707107 9.28027 2.65527)" fill="#E0C917"/>
+</g>
+<rect width="8.02659" height="2.00315" transform="matrix(-1 -8.74228e-08 -8.74228e-08 1 9.01318 1.99707)" fill="#E0C917"/>
+</svg>

theatre/studio/src/panels/SequenceEditorPanel/RightOverlay/Markers.tsx

@@ -0,0 +1,27 @@
+import type {Pointer} from '@theatre/dataverse'
+import {useVal} from '@theatre/react'
+import getStudio from '@theatre/studio/getStudio'
+import React from 'react'
+import type {SequenceEditorPanelLayout} from '@theatre/studio/panels/SequenceEditorPanel/layout/layout'
+import MarkerDot from './MarkerDot'
+
+const Markers: React.VFC<{layoutP: Pointer<SequenceEditorPanelLayout>}> = ({
+  layoutP,
+}) => {
+  const sheetAddress = useVal(layoutP.sheet.address)
+  const markerSetP =
+    getStudio().atomP.historic.projects.stateByProjectId[sheetAddress.projectId]
+      .stateBySheetId[sheetAddress.sheetId].sequenceEditor.markerSet
+  const markerAllIds = useVal(markerSetP.allIds)
+
+  return (
+    <>
+      {markerAllIds &&
+        Object.keys(markerAllIds).map((markerId) => (
+          <MarkerDot key={markerId} layoutP={layoutP} markerId={markerId} />
+        ))}
+    </>
+  )
+}
+
+export default Markers

theatre/studio/src/panels/SequenceEditorPanel/RightOverlay/Playhead.tsx

@@ -21,9 +21,12 @@ import BasicPopover from '@theatre/studio/uiComponents/Popover/BasicPopover'
 import PlayheadPositionPopover from './PlayheadPositionPopover'
 import {getIsPlayheadAttachedToFocusRange} from '@theatre/studio/UIRoot/useKeyboardShortcuts'
 import {
-  lockedCursorCssPropName,
+  lockedCursorCssVarName,
   useCssCursorLock,
 } from '@theatre/studio/uiComponents/PointerEventsHandler'
+import useContextMenu from '@theatre/studio/uiComponents/simpleContextMenu/useContextMenu'
+import getStudio from '@theatre/studio/getStudio'
+import {generateSequenceMarkerId} from '@theatre/shared/utils/ids'
 
 const Container = styled.div<{isVisible: boolean}>`
   --thumbColor: #00e0ff;
@@ -49,7 +52,7 @@ const Rod = styled.div`
 
   #pointer-root.draggingPositionInSequenceEditor &:not(.seeking) {
     /* pointer-events: auto; */
-    /* cursor: var(${lockedCursorCssPropName}); */
+    /* cursor: var(${lockedCursorCssVarName}); */
 
     &:after {
       position: absolute;
@@ -79,7 +82,7 @@ const Thumb = styled.div`
 
   #pointer-root.draggingPositionInSequenceEditor &:not(.seeking) {
     pointer-events: auto;
-    cursor: var(${lockedCursorCssPropName});
+    cursor: var(${lockedCursorCssVarName});
   }
 
   ${Container}.playheadattachedtofocusrange > & {
@@ -250,6 +253,11 @@ const Playhead: React.FC<{layoutP: Pointer<SequenceEditorPanelLayout>}> = ({
   // hide the frame stamp when seeking
   useLockFrameStampPosition(useVal(layoutP.seeker.isSeeking) || isDragging, -1)
 
+  const [contextMenu] = usePlayheadContextMenu(thumbNode, {
+    // pass in a pointer to ensure we aren't spending retrieval on every render
+    layoutP,
+  })
+
   return usePrism(() => {
     const isSeeking = val(layoutP.seeker.isSeeking)
 
@@ -270,6 +278,7 @@ const Playhead: React.FC<{layoutP: Pointer<SequenceEditorPanelLayout>}> = ({
 
     return (
       <>
+        {contextMenu}
         {popoverNode}
         <Container
           isVisible={isVisible}
@@ -306,3 +315,37 @@ const Playhead: React.FC<{layoutP: Pointer<SequenceEditorPanelLayout>}> = ({
 }
 
 export default Playhead
+
+function usePlayheadContextMenu(
+  node: HTMLElement | null,
+  options: {layoutP: Pointer<SequenceEditorPanelLayout>},
+) {
+  return useContextMenu(node, {
+    menuItems() {
+      return [
+        {
+          label: 'Place marker',
+          callback: () => {
+            getStudio().transaction(({stateEditors}) => {
+              // only retrieve val on callback to reduce unnecessary work on every use
+              const sheet = val(options.layoutP.sheet)
+              const sheetSequence = sheet.getSequence()
+              stateEditors.studio.historic.projects.stateByProjectId.stateBySheetId.sequenceEditor.replaceMarkers(
+                {
+                  sheetAddress: sheet.address,
+                  markers: [
+                    {
+                      id: generateSequenceMarkerId(),
+                      position: sheetSequence.position,
+                    },
+                  ],
+                  snappingFunction: sheetSequence.closestGridPosition,
+                },
+              )
+            })
+          },
+        },
+      ]
+    },
+  })
+}

theatre/studio/src/panels/SequenceEditorPanel/RightOverlay/RightOverlay.tsx

@@ -11,6 +11,7 @@ import HorizontalScrollbar from './HorizontalScrollbar'
 import Playhead from './Playhead'
 import TopStrip from './TopStrip'
 import FocusRangeCurtains from '@theatre/studio/panels/SequenceEditorPanel/DopeSheet/Right/FocusRangeCurtains'
+import Markers from './Markers'
 
 const Container = styled.div`
   position: absolute;
@@ -34,6 +35,7 @@ const RightOverlay: React.FC<{
         <HorizontalScrollbar layoutP={layoutP} />
         <FrameStamp layoutP={layoutP} />
         <TopStrip layoutP={layoutP} />
+        <Markers layoutP={layoutP} />
         <LengthIndicator layoutP={layoutP} />
         <FocusRangeCurtains layoutP={layoutP} />
       </Container>

theatre/studio/src/panels/SequenceEditorPanel/RightOverlay/SnapCursor.svg

@@ -0,0 +1,6 @@
+<svg width="34" height="34" viewBox="0 0 34 34" fill="none" xmlns="http://www.w3.org/2000/svg">
+  <path d="M1 7V1H7" stroke="#74FFDE" stroke-width="0.25" />
+  <path d="M7 33H1L1 27" stroke="#74FFDE" stroke-width="0.25" />
+  <path d="M33 27V33H27" stroke="#74FFDE" stroke-width="0.25" />
+  <path d="M27 1L33 1V7" stroke="#74FFDE" stroke-width="0.25" />
+</svg>

theatre/studio/src/panels/SequenceEditorPanel/SequenceEditorPanel.tsx

@@ -53,6 +53,7 @@ export const zIndexes = (() => {
     lengthIndicatorStrip: 0,
     playhead: 0,
     currentFrameStamp: 0,
+    marker: 0,
     horizontalScrollbar: 0,
   }
 

theatre/studio/src/store/stateEditors.ts

@@ -14,6 +14,7 @@ import type {
 import {encodePathToProp} from '@theatre/shared/utils/addresses'
 import type {
   KeyframeId,
+  SequenceMarkerId,
   SequenceTrackId,
   UIPanelId,
 } from '@theatre/shared/utils/ids'
@@ -40,6 +41,7 @@ import type {
   OutlineSelectionState,
   PanelPosition,
   StudioAhistoricState,
+  StudioHistoricStateSequenceEditorMarker,
 } from './types'
 import {clamp, uniq} from 'lodash-es'
 import {
@@ -52,6 +54,7 @@ import {
 import type SheetTemplate from '@theatre/core/sheets/SheetTemplate'
 import type SheetObjectTemplate from '@theatre/core/sheetObjects/SheetObjectTemplate'
 import type {PropTypeConfig} from '@theatre/core/propTypes'
+import {pointableSetUtil} from '@theatre/shared/utils/PointableSet'
 
 export const setDrafts__onlyMeantToBeCalledByTransaction = (
   drafts: undefined | Drafts,
@@ -250,6 +253,85 @@ namespace stateEditors {
                   ])
                 }
               }
+
+              function _ensureMarkers(sheetAddress: SheetAddress) {
+                const sequenceEditor =
+                  stateEditors.studio.historic.projects.stateByProjectId.stateBySheetId._ensure(
+                    sheetAddress,
+                  ).sequenceEditor
+
+                if (!sequenceEditor.markerSet) {
+                  sequenceEditor.markerSet = pointableSetUtil.create()
+                }
+
+                return sequenceEditor.markerSet
+              }
+
+              export function replaceMarkers(p: {
+                sheetAddress: SheetAddress
+                markers: Array<StudioHistoricStateSequenceEditorMarker>
+                snappingFunction: (p: number) => number
+              }) {
+                const currentMarkerSet = _ensureMarkers(p.sheetAddress)
+
+                const sanitizedMarkers = p.markers
+                  .filter((marker) => {
+                    if (!isFinite(marker.position)) return false
+
+                    return true // marker looks valid
+                  })
+                  .map((marker) => ({
+                    ...marker,
+                    position: p.snappingFunction(marker.position),
+                  }))
+
+                const newMarkersById = keyBy(sanitizedMarkers, 'id')
+
+                /** Usually starts as the "unselected" markers */
+                let markersThatArentBeingReplaced = pointableSetUtil.filter(
+                  currentMarkerSet,
+                  (marker) => marker && !newMarkersById[marker.id],
+                )
+
+                const markersThatArentBeingReplacedByPosition = keyBy(
+                  Object.values(markersThatArentBeingReplaced.byId),
+                  'position',
+                )
+
+                // If the new transformed markers overlap with any existing markers,
+                // we remove the overlapped markers
+                sanitizedMarkers.forEach(({position}) => {
+                  const existingMarkerAtThisPosition =
+                    markersThatArentBeingReplacedByPosition[position]
+                  if (existingMarkerAtThisPosition) {
+                    markersThatArentBeingReplaced = pointableSetUtil.remove(
+                      markersThatArentBeingReplaced,
+                      existingMarkerAtThisPosition.id,
+                    )
+                  }
+                })
+
+                Object.assign(
+                  currentMarkerSet,
+                  pointableSetUtil.merge([
+                    markersThatArentBeingReplaced,
+                    pointableSetUtil.create(
+                      sanitizedMarkers.map((marker) => [marker.id, marker]),
+                    ),
+                  ]),
+                )
+              }
+
+              export function removeMarker(options: {
+                sheetAddress: SheetAddress
+                markerId: SequenceMarkerId
+              }) {
+                const currentMarkerSet = _ensureMarkers(options.sheetAddress)
+                Object.assign(
+                  currentMarkerSet,
+                  pointableSetUtil.remove(currentMarkerSet, options.markerId),
+                )
+              }
             }
           }
         }
@@ -574,6 +656,9 @@ namespace stateEditors {
             )
             if (indexOfLeftKeyframe === -1) {
               keyframes.unshift({
+                // generating the keyframe within the `setKeyframeAtPosition` makes it impossible for us
+                // to make this business logic deterministic, which is important to guarantee for collaborative
+                // editing.
                 id: generateKeyframeId(),
                 position,
                 connectedRight: true,

theatre/studio/src/store/types/historic.ts

@@ -8,6 +8,7 @@ import type {
   WithoutSheetInstance,
 } from '@theatre/shared/utils/addresses'
 import type {StrictRecord} from '@theatre/shared/utils/types'
+import type {PointableSet} from '@theatre/shared/utils/PointableSet'
 import type Project from '@theatre/core/projects/Project'
 import type Sheet from '@theatre/core/sheets/Sheet'
 import type SheetObject from '@theatre/core/sheetObjects/SheetObject'
@@ -15,6 +16,7 @@ import type {
   ObjectAddressKey,
   PaneInstanceId,
   ProjectId,
+  SequenceMarkerId,
   SheetId,
   SheetInstanceId,
   UIPanelId,
@@ -69,6 +71,22 @@ export type PaneInstanceDescriptor = {
   paneClass: string
 }
 
+/**
+ * Marker allows you to mark notable positions in your sequence.
+ *
+ * See root {@link StudioHistoricState}
+ */
+export type StudioHistoricStateSequenceEditorMarker = {
+  id: SequenceMarkerId
+  /**
+   * The position this marker takes in the sequence.
+   *
+   * Usually, this value is measured in seconds, but the unit could be varied based on the kind of
+   * unit you're using for mapping to the position (e.g. Position=1 = 10px of scrolling)
+   */
+  position: number
+}
+
 /**
  * See parent {@link StudioHistoricStateProject}.
  * See root {@link StudioHistoricState}
@@ -76,6 +94,10 @@ export type PaneInstanceDescriptor = {
 export type StudioHistoricStateProjectSheet = {
   selectedInstanceId: undefined | SheetInstanceId
   sequenceEditor: {
+    markerSet?: PointableSet<
+      SequenceMarkerId,
+      StudioHistoricStateSequenceEditorMarker
+    >
     selectedPropsByObject: StrictRecord<
       ObjectAddressKey,
       StrictRecord<PathToProp_Encoded, keyof typeof graphEditorColors>
@@ -88,16 +110,6 @@ export type StudioHistoricStateProject = {
   stateBySheetId: StrictRecord<SheetId, StudioHistoricStateProjectSheet>
 }
 
-/**
- * {@link StudioHistoricState} includes both studio and project data, and
- * contains data changed for an undo/redo history.
- *
- * ## Internally
- *
- * We use immer `Draft`s to encapsulate this whole state to then be operated
- * on by each transaction. The derived values from the store will also include
- * the application of the "temp transactions" stack.
- */
 export type StudioHistoricState = {
   projects: {
     stateByProjectId: StrictRecord<ProjectId, StudioHistoricStateProject>

theatre/studio/src/uiComponents/PointerEventsHandler.tsx

@@ -12,12 +12,14 @@ import styled from 'styled-components'
 const elementId = 'pointer-root'
 
 /**
- * When the cursor is locked, this css prop is added to #pointer-root
+ * When the cursor is locked, this css var is added to #pointer-root
  * whose value will be the locked cursor (e.g. ew-resize).
  *
  * Look up references of this constant for examples of how it is used.
+ *
+ * See {@link useCssCursorLock} - code that locks the cursor
  */
-export const lockedCursorCssPropName = '--lockedCursor'
+export const lockedCursorCssVarName = '--lockedCursor'
 
 const Container = styled.div`
   pointer-events: auto;
@@ -73,7 +75,7 @@ const PointerEventsHandler: React.FC<{
           style={{
             cursor: lockedCursor,
             // @ts-ignore
-            [lockedCursorCssPropName]: lockedCursor,
+            [lockedCursorCssVarName]: lockedCursor,
           }}
         >
           {props.children}
@@ -94,6 +96,8 @@ const PointerEventsHandler: React.FC<{
  * but then "unlocking" that style will again reveal the existing styles.
  *
  * It behaves a bit like a stack.
+ *
+ * See {@link lockedCursorCssVarName}
  */
 export const useCssCursorLock = (
   /** Whether to enable the provided cursor style */

theatre/studio/src/uiComponents/useDrag.ts

@@ -80,10 +80,10 @@ export default function useDrag(
     }
   }>({dragHappened: false, startPos: {x: 0, y: 0}})
 
+  const capturedPointerRef = useRef<undefined | CapturedPointer>()
   useLayoutEffect(() => {
     if (!target) return
 
-    let capturedPointer: undefined | CapturedPointer
     const getDistances = (event: MouseEvent): [number, number] => {
       const {startPos} = stateRef.current
       return [event.screenX - startPos.x, event.screenY - startPos.y]
@@ -98,11 +98,12 @@ export default function useDrag(
     }
 
     const dragEndHandler = () => {
-      removeDragListeners()
+      if (modeRef.current === 'dragging') {
-      modeRef.current = 'notDragging'
+        removeDragListeners()
+        modeRef.current = 'notDragging'
 
-      optsRef.current.onDragEnd &&
+        optsRef.current.onDragEnd?.(stateRef.current.dragHappened)
-        optsRef.current.onDragEnd(stateRef.current.dragHappened)
+      }
     }
 
     const addDragListeners = () => {
@@ -111,7 +112,7 @@ export default function useDrag(
     }
 
     const removeDragListeners = () => {
-      capturedPointer?.release()
+      capturedPointerRef.current?.release()
       document.removeEventListener('mousemove', dragHandler)
       document.removeEventListener('mouseup', dragEndHandler)
     }
@@ -132,7 +133,7 @@ export default function useDrag(
 
     const dragStartHandler = (event: MouseEvent) => {
       // defensively release
-      capturedPointer?.release()
+      capturedPointerRef.current?.release()
 
       const opts = optsRef.current
       if (opts.disabled === true) return
@@ -147,7 +148,7 @@ export default function useDrag(
       }
 
       // need to capture pointer after we know the provided handler wants to handle drag start
-      capturedPointer = capturePointer('Drag start')
+      capturedPointerRef.current = capturePointer('Drag start')
 
       if (!opts.dontBlockMouseDown) {
         event.stopPropagation()
@@ -176,8 +177,7 @@ export default function useDrag(
       target.removeEventListener('click', preventUnwantedClick as $FixMe)
 
       if (modeRef.current !== 'notDragging') {
-        optsRef.current.onDragEnd &&
+        optsRef.current.onDragEnd?.(modeRef.current === 'dragging')
-          optsRef.current.onDragEnd(modeRef.current === 'dragging')
       }
       modeRef.current = 'notDragging'
     }