DEV: Refactor header offset calculations (#29398)

app/assets/javascripts/discourse/app/components/glimmer-site-header.gjs

@@ -22,6 +22,7 @@ import Header from "./header";
 
 let _menuPanelClassesToForceDropdown = [];
 const PANEL_WIDTH = 340;
+const DEBOUNCE_HEADER_DELAY = 10;
 
 export default class GlimmerSiteHeader extends Component {
   @service appEvents;
@@ -36,6 +37,7 @@ export default class GlimmerSiteHeader extends Component {
   @tracked _dockedHeader = false;
   _animate = false;
   _headerWrap;
+  _mainOutletWrapper;
   _swipeMenuOrigin;
   _applicationElement;
   _resizeObserver;
@@ -69,42 +71,51 @@ export default class GlimmerSiteHeader extends Component {
   }
 
   @bind
-  updateHeaderOffset() {
-    // Safari likes overscolling the page (on both iOS and macOS).
-    // This shows up as a negative value in window.scrollY.
-    // We can use this to offset the headerWrap's top offset to avoid
-    // jitteriness and bad positioning.
-    const windowOverscroll = Math.min(0, window.scrollY);
-
-    // The headerWrap's top offset can also be a negative value on Safari,
-    // because of the changing height of the viewport (due to the URL bar).
-    // For our use case, it's best to ensure this is clamped to 0.
-    const headerWrapTop = Math.max(
+  updateOffsets() {
+    // clamping to 0 to prevent negative values (hello, Safari)
+    const headerWrapBottom = Math.max(
       0,
-      Math.floor(this._headerWrap.getBoundingClientRect().top)
+      Math.floor(this._headerWrap.getBoundingClientRect().bottom)
+    );
+
+    let mainOutletOffsetTop = Math.max(
+      0,
+      Math.floor(this._mainOutletWrapper.getBoundingClientRect().top) -
+        headerWrapBottom
     );
-    let offsetTop = headerWrapTop + windowOverscroll;
 
     if (DEBUG && isTesting()) {
-      offsetTop -= document
+      mainOutletOffsetTop -= document
         .getElementById("ember-testing-container")
         .getBoundingClientRect().top;
 
-      offsetTop -= 1; // For 1px border on testing container
+      mainOutletOffsetTop -= 1; // For 1px border on testing container
     }
 
-    const documentStyle = document.documentElement.style;
-    const currentValue =
-      parseInt(documentStyle.getPropertyValue("--header-offset"), 10) || 0;
-    const newValue = this._headerWrap.offsetHeight + offsetTop;
-    if (currentValue !== newValue) {
-      documentStyle.setProperty("--header-offset", `${newValue}px`);
+    const docStyle = document.documentElement.style;
+    const currentHeaderOffset =
+      parseInt(docStyle.getPropertyValue("--header-offset"), 10) || 0;
+    const newHeaderOffset = headerWrapBottom;
+    if (currentHeaderOffset !== newHeaderOffset) {
+      docStyle.setProperty("--header-offset", `${newHeaderOffset}px`);
+    }
+
+    const currentMainOutletOffset =
+      parseInt(docStyle.getPropertyValue("--main-outlet-offset"), 10) || 0;
+    const newMainOutletOffset = headerWrapBottom + mainOutletOffsetTop;
+    if (currentMainOutletOffset !== newMainOutletOffset) {
+      docStyle.setProperty("--main-outlet-offset", `${newMainOutletOffset}px`);
     }
   }
 
+  @debounce(DEBOUNCE_HEADER_DELAY)
+  _recalculateHeaderOffset() {
+    this._scheduleUpdateOffsets();
+  }
+
   @bind
-  _onScroll() {
-    schedule("afterRender", this.updateHeaderOffset);
+  _scheduleUpdateOffsets() {
+    schedule("afterRender", this.updateOffsets);
   }
 
   @action
@@ -119,17 +130,13 @@ export default class GlimmerSiteHeader extends Component {
     }
 
     this._headerWrap = document.querySelector(".d-header-wrap");
+    this._mainOutletWrapper = document.querySelector("#main-outlet-wrapper");
     if (this._headerWrap) {
       schedule("afterRender", () => {
         this.headerElement = this._headerWrap.querySelector("header.d-header");
-        this.updateHeaderOffset();
-        document.documentElement.style.setProperty(
-          "--header-top",
-          `${this.headerElement.offsetTop}px`
-        );
       });
 
-      window.addEventListener("scroll", this._onScroll, {
+      window.addEventListener("scroll", this._recalculateHeaderOffset, {
         passive: true,
       });
 
@@ -137,20 +144,11 @@ export default class GlimmerSiteHeader extends Component {
       const dirs = ["up", "down"];
       this._itsatrap.bind(dirs, (e) => this._handleArrowKeysNav(e));
 
-      this._resizeObserver = new ResizeObserver((entries) => {
-        for (let entry of entries) {
-          if (entry.contentRect) {
-            const headerTop = this.headerElement?.offsetTop;
-            document.documentElement.style.setProperty(
-              "--header-top",
-              `${headerTop}px`
-            );
-            this.updateHeaderOffset();
-          }
-        }
+      this._resizeObserver = new ResizeObserver(() => {
+        this._recalculateHeaderOffset();
       });
 
-      this._resizeObserver.observe(this._headerWrap);
+      this._resizeObserver.observe(document.querySelector(".discourse-root"));
     }
   }
 
@@ -410,7 +408,7 @@ export default class GlimmerSiteHeader extends Component {
     this._itsatrap?.destroy();
     this._itsatrap = null;
 
-    window.removeEventListener("scroll", this._onScroll);
+    window.removeEventListener("scroll", this._recalculateHeaderOffset);
     this._resizeObserver?.disconnect();
   }
 

app/assets/stylesheets/common/base/menu-panel.scss

@@ -16,7 +16,7 @@
   // positions are relative to the .d-header .panel div
   top: 100%; // directly underneath .panel
   right: -10px; // 10px to the right of .panel - adjust as needed
-  max-height: 80vh;
+  max-height: calc(100dvh - var(--header-offset) - 1em);
   border-radius: var(--d-border-radius-large);
 }
 
@@ -660,14 +660,14 @@
   width: 100%;
   position: fixed;
   background-color: rgba(0, 0, 0, 0.3);
-  top: var(--header-top);
+  top: 0;
   left: 0;
   display: none;
   touch-action: pan-y pinch-zoom;
 }
 
 .menu-panel.slide-in {
-  top: var(--header-top);
+  top: 0;
   box-sizing: border-box;
   // ensure there's always space to click outside on tiny devices
   max-width: 90vw;
@@ -678,11 +678,5 @@
   }
   box-shadow: 0px 0 30px -2px rgba(0, 0, 0, 0.5);
 
-  --base-height: calc(var(--100dvh) - var(--header-top));
-
-  height: var(--base-height);
-
-  html.footer-nav-ipad & {
-    height: calc(var(--base-height) - var(--footer-nav-height));
-  }
+  height: var(--100dvh);
 }

app/assets/stylesheets/common/base/sidebar.scss

@@ -45,7 +45,7 @@
   display: flex;
   grid-area: sidebar;
   position: sticky;
-  top: var(--header-offset);
+  top: var(--main-outlet-offset);
   background: var(--d-sidebar-background);
 
   @include unselectable;
@@ -57,7 +57,7 @@
   }
 
   height: calc(
-    var(--composer-vh, var(--1dvh)) * 100 - var(--header-offset, 0px)
+    var(--composer-vh, var(--1dvh)) * 100 - var(--main-outlet-offset, 0px)
   );
 
   align-self: start;

app/assets/stylesheets/desktop/menu-panel.scss

@@ -5,7 +5,6 @@
 
   &.drop-down {
     .panel-body {
-      max-height: calc(100vh - var(--header-offset));
       max-width: calc(100vw - 2em);
     }
   }

plugins/chat/assets/stylesheets/common/base-common.scss

@@ -191,7 +191,7 @@ body.has-full-page-chat {
 
   .c-navbar-container {
     position: sticky;
-    top: var(--header-offset);
+    top: var(--main-outlet-offset);
   }
 
   .chat-messages-scroller {

plugins/chat/assets/stylesheets/common/chat-composer.scss

@@ -87,7 +87,7 @@
     resize: none;
     max-height: calc(
       (
-          var(--100dvh) - var(--header-offset, 0px) -
+          var(--100dvh) - var(--main-outlet-offset, 0px) -
             var(--chat-header-offset, 0px)
         ) / 100 * 25
     );

plugins/chat/assets/stylesheets/common/chat-height-mixin.scss

@@ -2,7 +2,8 @@
   // desktop and mobile
   // -1px is for the bottom border of the chat navbar
   $base-height: calc(
-    var(--composer-vh, 1vh) * 100 - var(--header-offset, 0px) - 1px - $inset
+    var(--composer-vh, 1vh) * 100 - var(--main-outlet-offset, 0px) - 1px -
+      $inset
   );
 
   height: calc($base-height - var(--composer-height, 0px));

plugins/chat/assets/stylesheets/desktop/chat-index-full-page.scss

@@ -1,7 +1,7 @@
 .has-full-page-chat:not(.discourse-sidebar) {
   .full-page-chat {
     .channels-list {
-      height: calc(100vh - var(--header-offset));
+      height: calc(100vh - var(--main-outlet-offset));
       border-right: 1px solid var(--primary-low);
       background: var(--secondary);
       overflow-y: auto;