From 7cfee215f4837d3051896eaede226633514ba9ad Mon Sep 17 00:00:00 2001
From: Marijn Haverbeke <marijn@haverbeke.nl>
Date: Wed, 15 Dec 2021 09:38:01 +0100
Subject: [PATCH] Force a content measure when the editor comes into view

FIX: Fix a bug that could cause the editor to not measure its layout the first time
it came into view.

See https://discuss.codemirror.net/t/bug-gutters-height-miscalculate-when-the-view-is-not-on-viewport/3812
---
 src/domobserver.ts | 2 +-
 src/viewstate.ts   | 6 +++++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/domobserver.ts b/src/domobserver.ts
index 55d87c6a..c2550fe9 100644
--- a/src/domobserver.ts
+++ b/src/domobserver.ts
@@ -99,7 +99,7 @@ export class DOMObserver {
     if (typeof IntersectionObserver == "function") {
       this.intersection = new IntersectionObserver(entries => {
         if (this.parentCheck < 0) this.parentCheck = setTimeout(this.listenForScroll.bind(this), 1000)
-        if (entries.length > 0 && entries[entries.length - 1].intersectionRatio > 0 != this.intersecting) {
+        if (entries.length > 0 && (entries[entries.length - 1].intersectionRatio > 0) != this.intersecting) {
           this.intersecting = !this.intersecting
           if (this.intersecting != this.view.inView)
             this.onScrollChanged(document.createEvent("Event"))
diff --git a/src/viewstate.ts b/src/viewstate.ts
index d4ffcb7c..2d6e1a3b 100644
--- a/src/viewstate.ts
+++ b/src/viewstate.ts
@@ -239,7 +239,11 @@ export class ViewState {
     let pixelViewport = this.printing ? {top: -1e8, bottom: 1e8, left: -1e8, right: 1e8} : visiblePixelRange(dom, this.paddingTop)
     let dTop = pixelViewport.top - this.pixelViewport.top, dBottom = pixelViewport.bottom - this.pixelViewport.bottom
     this.pixelViewport = pixelViewport
-    this.inView = this.pixelViewport.bottom > this.pixelViewport.top && this.pixelViewport.right > this.pixelViewport.left
+    let inView = this.pixelViewport.bottom > this.pixelViewport.top && this.pixelViewport.right > this.pixelViewport.left
+    if (inView != this.inView) {
+      this.inView = inView
+      if (inView) measureContent = true
+    }
     if (!this.inView) return 0
 
     if (measureContent) {