From da72a079ae8a98b792e3df54404468e9b041b892 Mon Sep 17 00:00:00 2001
From: Andrew Kingston <aptkingston@ssl-mail.com>
Date: Thu, 10 Jun 2021 15:13:51 +0100
Subject: [PATCH] Use IntersectionObservers to determine visibility of selected
 and hovered components

---
 .../client/src/components/ClientApp.svelte    |  13 ++-
 .../src/components/HoverIndicator.svelte      |  60 +---------
 .../client/src/components/Indicator.svelte    |  13 ++-
 .../client/src/components/IndicatorSet.svelte | 110 ++++++++++++++++++
 .../src/components/SelectionIndicator.svelte  |  59 ++--------
 5 files changed, 139 insertions(+), 116 deletions(-)
 create mode 100644 packages/client/src/components/IndicatorSet.svelte

diff --git a/packages/client/src/components/ClientApp.svelte b/packages/client/src/components/ClientApp.svelte
index 01bbe6c9af..7bdab63102 100644
--- a/packages/client/src/components/ClientApp.svelte
+++ b/packages/client/src/components/ClientApp.svelte
@@ -68,13 +68,20 @@
         <Component definition={$screenStore.activeLayout.props} />
       </div>
       <NotificationDisplay />
+      <!-- Key block needs to be outside the if statement or it breaks -->
       {#key $builderStore.selectedComponentId}
-        {#if $builderStore.inBuilder && $builderStore.selectedComponent}
+        {#if $builderStore.inBuilder}
           <SettingsBar />
-          <SelectionIndicator />
-          <HoverIndicator />
         {/if}
       {/key}
+      <!--
+        We don't want to key these by componentID as they control their own
+        re-mounting to avoid flashes.
+      -->
+      {#if $builderStore.inBuilder}
+        <SelectionIndicator />
+        <HoverIndicator />
+      {/if}
     </Provider>
   </div>
 {/if}
diff --git a/packages/client/src/components/HoverIndicator.svelte b/packages/client/src/components/HoverIndicator.svelte
index bb5db38d73..55e6876190 100644
--- a/packages/client/src/components/HoverIndicator.svelte
+++ b/packages/client/src/components/HoverIndicator.svelte
@@ -1,86 +1,32 @@
 <script>
   import { onMount, onDestroy } from "svelte"
+  import IndicatorSet from "./IndicatorSet.svelte"
   import { builderStore } from "../store"
-  import Indicator from "./Indicator.svelte"
-  import { domDebounce } from "../utils/domDebounce"
 
-  let indicators = []
-  let interval
   let componentId
-  let componentName
-
-  const updatePosition = () => {
-    let newIndicators = []
-
-    if (componentId) {
-      const parents = document.getElementsByClassName(componentId)
-
-      // Batch reads to minimize reflow
-      const scrollX = window.scrollX
-      const scrollY = window.scrollY
-
-      for (let i = 0; i < parents.length; i++) {
-        const child = parents[i]?.childNodes?.[0]
-        if (child) {
-          const elBounds = child.getBoundingClientRect()
-          newIndicators.push({
-            top: elBounds.top + scrollY - 2,
-            left: elBounds.left + scrollX - 2,
-            width: elBounds.width + 4,
-            height: elBounds.height + 4,
-          })
-        }
-      }
-    }
-
-    indicators = newIndicators
-  }
-  const debouncedUpdate = domDebounce(updatePosition)
+  $: zIndex = componentId === $builderStore.selectedComponentId ? 900 : 920
 
   const onMouseOver = e => {
     const element = e.target.closest("[data-type='component']")
     const newId = element?.dataset?.id
-    const newName = element?.dataset?.name
     if (newId !== componentId) {
       componentId = newId
-      componentName = newName
-      debouncedUpdate()
     }
   }
 
   const onMouseLeave = () => {
     componentId = null
-    componentName = null
   }
 
   onMount(() => {
-    debouncedUpdate()
-    interval = setInterval(debouncedUpdate, 100)
     document.addEventListener("mouseover", onMouseOver)
     document.addEventListener("mouseleave", onMouseLeave)
-    document.addEventListener("scroll", debouncedUpdate, true)
   })
 
   onDestroy(() => {
-    clearInterval(interval)
     document.removeEventListener("mouseover", onMouseOver)
     document.removeEventListener("mouseleave", onMouseLeave)
-    document.removeEventListener("scroll", debouncedUpdate, true)
   })
 </script>
 
-{#key componentId}
-  {#if componentId !== $builderStore.selectedComponentId}
-    {#each indicators as indicator, idx}
-      <Indicator
-        top={indicator.top}
-        left={indicator.left}
-        width={indicator.width}
-        height={indicator.height}
-        text={idx === 0 ? componentName : null}
-        color="rgb(120, 170, 244)"
-        transition
-      />
-    {/each}
-  {/if}
-{/key}
+<IndicatorSet {componentId} color="rgb(120, 170, 244)" transition {zIndex} />
diff --git a/packages/client/src/components/Indicator.svelte b/packages/client/src/components/Indicator.svelte
index b47d5ee4ba..fb1b5f320f 100644
--- a/packages/client/src/components/Indicator.svelte
+++ b/packages/client/src/components/Indicator.svelte
@@ -7,13 +7,18 @@
   export let height
   export let text
   export let color
+  export let zIndex
   export let transition = false
 </script>
 
 <div
-  in:fade={{ delay: transition ? 65 : 0, duration: transition ? 130 : 0 }}
+  in:fade={{
+    delay: transition ? 50 : 0,
+    duration: transition ? 130 : 0,
+  }}
+  out:fade={{ duration: transition ? 130 : 0 }}
   class="indicator"
-  style="top: {top}px; left: {left}px; width: {width}px; height: {height}px; --color: {color};"
+  style="top: {top}px; left: {left}px; width: {width}px; height: {height}px; --color: {color}; --zIndex: {zIndex};"
 >
   {#if text}
     <div class="text" class:flipped={top < 22}>
@@ -24,8 +29,8 @@
 
 <style>
   .indicator {
-    position: absolute;
-    z-index: 910;
+    position: fixed;
+    z-index: var(--zIndex);
     border: 2px solid var(--color);
     pointer-events: none;
     border-radius: 4px;
diff --git a/packages/client/src/components/IndicatorSet.svelte b/packages/client/src/components/IndicatorSet.svelte
new file mode 100644
index 0000000000..4ba6efd085
--- /dev/null
+++ b/packages/client/src/components/IndicatorSet.svelte
@@ -0,0 +1,110 @@
+<script>
+  import { onMount, onDestroy } from "svelte"
+  import Indicator from "./Indicator.svelte"
+  import { domDebounce } from "../utils/domDebounce"
+
+  export let componentId
+  export let color
+  export let transition
+  export let zIndex
+
+  let indicators = []
+  let interval
+  let text
+  $: visibleIndicators = indicators.filter(x => x.visible)
+
+  let updating = false
+  let observers = []
+  let callbackCount = 0
+  let nextIndicators = []
+
+  const createIntersectionCallback = idx => entries => {
+    if (callbackCount >= observers.length) {
+      return
+    }
+    nextIndicators[idx].visible = entries[0].isIntersecting
+    if (++callbackCount === observers.length) {
+      indicators = nextIndicators
+      updating = false
+    }
+  }
+
+  const updatePosition = () => {
+    if (updating) {
+      return
+    }
+
+    // Sanity check
+    if (!componentId) {
+      indicators = []
+      return
+    }
+
+    // Reset state
+    updating = true
+    callbackCount = 0
+    observers.forEach(o => o.disconnect())
+    observers = []
+    nextIndicators = []
+
+    // Determine next set of indicators
+    const parents = document.getElementsByClassName(componentId)
+    if (parents.length) {
+      text = parents[0].dataset.name
+    }
+
+    // Batch reads to minimize reflow
+    const scrollX = window.scrollX
+    const scrollY = window.scrollY
+
+    // Extract valid children
+    const children = Array.from(parents)
+      .map(parent => parent?.childNodes?.[0])
+      .filter(child => child != null)
+
+    children.forEach((child, idx) => {
+      const callback = createIntersectionCallback(idx)
+      const threshold = children.length > 1 ? 1 : 0
+      const observer = new IntersectionObserver(callback, { threshold })
+      observer.observe(child)
+      observers.push(observer)
+
+      const elBounds = child.getBoundingClientRect()
+      nextIndicators.push({
+        top: elBounds.top + scrollY - 2,
+        left: elBounds.left + scrollX - 2,
+        width: elBounds.width + 4,
+        height: elBounds.height + 4,
+        visible: false,
+      })
+    })
+  }
+  const debouncedUpdate = domDebounce(updatePosition)
+
+  onMount(() => {
+    debouncedUpdate()
+    interval = setInterval(debouncedUpdate, 100)
+    document.addEventListener("scroll", debouncedUpdate, true)
+  })
+
+  onDestroy(() => {
+    clearInterval(interval)
+    document.removeEventListener("scroll", debouncedUpdate, true)
+    observers.forEach(o => o.disconnect())
+  })
+</script>
+
+{#key componentId}
+  {#each visibleIndicators as indicator, idx}
+    <Indicator
+      top={indicator.top}
+      left={indicator.left}
+      width={indicator.width}
+      height={indicator.height}
+      text={idx === 0 ? text : null}
+      {transition}
+      {zIndex}
+      {color}
+    />
+  {/each}
+{/key}
diff --git a/packages/client/src/components/SelectionIndicator.svelte b/packages/client/src/components/SelectionIndicator.svelte
index 5e9a82e721..e53e774b8e 100644
--- a/packages/client/src/components/SelectionIndicator.svelte
+++ b/packages/client/src/components/SelectionIndicator.svelte
@@ -1,56 +1,11 @@
 <script>
-  import { onMount, onDestroy } from "svelte"
   import { builderStore } from "../store"
-  import Indicator from "./Indicator.svelte"
-  import { domDebounce } from "../utils/domDebounce"
-
-  let indicators = []
-  let interval
-
-  const updatePosition = () => {
-    const id = $builderStore.selectedComponentId
-    const parents = document.getElementsByClassName(id)
-
-    // Batch reads to minimize reflow
-    const scrollX = window.scrollX
-    const scrollY = window.scrollY
-
-    let newIndicators = []
-    for (let i = 0; i < parents.length; i++) {
-      const child = parents[i]?.childNodes?.[0]
-      if (child) {
-        const elBounds = child.getBoundingClientRect()
-        newIndicators.push({
-          top: elBounds.top + scrollY - 2,
-          left: elBounds.left + scrollX - 2,
-          width: elBounds.width + 4,
-          height: elBounds.height + 4,
-        })
-      }
-    }
-    indicators = newIndicators
-  }
-  const debouncedUpdate = domDebounce(updatePosition)
-
-  onMount(() => {
-    debouncedUpdate()
-    interval = setInterval(debouncedUpdate, 100)
-    document.addEventListener("scroll", debouncedUpdate, true)
-  })
-
-  onDestroy(() => {
-    clearInterval(interval)
-    document.removeEventListener("scroll", debouncedUpdate, true)
-  })
+  import IndicatorSet from "./IndicatorSet.svelte"
 </script>
 
-{#each indicators as indicator, idx}
-  <Indicator
-    top={indicator.top}
-    left={indicator.left}
-    width={indicator.width}
-    height={indicator.height}
-    text={idx === 0 ? $builderStore.selectedComponent._instanceName : null}
-    color="rgb(66, 133, 244)"
-  />
-{/each}
+<IndicatorSet
+  componentId={$builderStore.selectedComponentId}
+  color="rgb(66, 133, 244)"
+  zIndex="910"
+  transition
+/>