Paginator: prevent spread in portrait

Or, for vertical writing, in landscape

README.md

@@ -179,7 +179,7 @@ The layout can be configured by setting the following attributes:
 - `gap`: a CSS `<percentage>`. The size of the space between columns, relative to page size.
 - `max-inline-size`: a CSS `<length>`. The unit must be `px`. The maximum inline size of the text (column width in paginated mode).
 - `max-block-size`: same as above, but for the size in the block direction.
-- `max-column-count`: integer. The maximum number of columns. Has no effect in scrolled mode.
+- `max-column-count`: integer. The maximum number of columns. Has no effect in scrolled mode, or when the orientation of the renderer element is `portrait` (or, for vertical writing, `landscape`).
 
 (Note: there's no JS property API. You must use `.setAttribute()`.)
 

paginator.js

@@ -376,6 +376,7 @@ export class Paginator extends HTMLElement {
     ]
     #root = this.attachShadow({ mode: 'closed' })
     #observer = new ResizeObserver(() => this.render())
+    #top
     #background
     #container
     #header
@@ -399,21 +400,27 @@ export class Paginator extends HTMLElement {
         super()
         this.#root.innerHTML = `<style>
         :host {
+            display: block;
+            container-type: size;
+        }
+        :host, #top {
+            box-sizing: border-box;
+            position: relative;
+            overflow: hidden;
+            width: 100%;
+            height: 100%;
+        }
+        #top {
             --_gap: 7%;
             --_margin: 48px;
             --_max-inline-size: 720px;
             --_max-block-size: 1440px;
             --_max-column-count: 2;
-            --_vertical: 0;
+            --_max-column-count-portrait: 1;
+            --_max-column-count-spread: var(--_max-column-count);
             --_half-gap: calc(var(--_gap) / 2);
-            --_max-width: calc(
+            --_max-width: calc(var(--_max-inline-size) * var(--_max-column-count-spread));
-                var(--_vertical) * var(--_max-block-size)
+            --_max-height: var(--_max-block-size);
-                + (1 - var(--_vertical)) * var(--_max-inline-size) * var(--_max-column-count)
-            );
-            --_max-height: calc(
-                var(--_vertical) * var(--_max-inline-size) * var(--_max-column-count)
-                + (1 - var(--_vertical)) * var(--_max-block-size)
-            );
             display: grid;
             grid-template-columns:
                 minmax(var(--_half-gap), 1fr)
@@ -423,11 +430,19 @@ export class Paginator extends HTMLElement {
                 minmax(var(--_margin), 1fr)
                 minmax(0, var(--_max-height))
                 minmax(var(--_margin), 1fr);
-            box-sizing: border-box;
+            &.vertical {
-            position: relative;
+                --_max-column-count-spread: var(--_max-column-count-portrait);
-            overflow: hidden;
+                --_max-width: var(--_max-block-size);
-            width: 100%;
+                --_max-height: calc(var(--_max-inline-size) * var(--_max-column-count-spread));
-            height: 100%;
+            }
+            @container (orientation: portrait) {
+                & {
+                    --_max-column-count-spread: var(--_max-column-count-portrait);
+                }
+                &.vertical {
+                    --_max-column-count-spread: var(--_max-column-count);
+                }
+            }
         }
         #background {
             grid-column-start: 1;
@@ -475,12 +490,15 @@ export class Paginator extends HTMLElement {
             opacity: .6;
         }
         </style>
+        <div id="top">
             <div id="background" part="filter"></div>
             <div id="header"></div>
             <div id="container"></div>
             <div id="footer"></div>
+        </div>
         `
 
+        this.#top = this.#root.getElementById('top')
         this.#background = this.#root.getElementById('background')
         this.#container = this.#root.getElementById('container')
         this.#header = this.#root.getElementById('header')
@@ -519,11 +537,11 @@ export class Paginator extends HTMLElement {
             case 'margin':
             case 'max-block-size':
             case 'max-column-count':
-                this.style.setProperty('--_' + name, value)
+                this.#top.style.setProperty('--_' + name, value)
                 break
             case 'max-inline-size':
                 // needs explicit `render()` as it doesn't necessarily resize
-                this.style.setProperty('--_' + name, value)
+                this.#top.style.setProperty('--_' + name, value)
                 this.render()
                 break
         }
@@ -547,7 +565,7 @@ export class Paginator extends HTMLElement {
     #beforeRender({ vertical, rtl, background }) {
         this.#vertical = vertical
         this.#rtl = rtl
-        this.style.setProperty('--_vertical', vertical ? 1 : 0)
+        this.#top.classList.toggle('vertical', vertical)
 
         // set background to `doc` background
         // this is needed because the iframe does not fill the whole element
@@ -556,9 +574,9 @@ export class Paginator extends HTMLElement {
         const { width, height } = this.#container.getBoundingClientRect()
         const size = vertical ? height : width
 
-        const style = getComputedStyle(this)
+        const style = getComputedStyle(this.#top)
         const maxInlineSize = parseFloat(style.getPropertyValue('--_max-inline-size'))
-        const maxColumnCount = parseInt(style.getPropertyValue('--_max-column-count'))
+        const maxColumnCount = parseInt(style.getPropertyValue('--_max-column-count-spread'))
         const margin = parseFloat(style.getPropertyValue('--_margin'))
         this.#margin = margin
 
@@ -586,7 +604,7 @@ export class Paginator extends HTMLElement {
         if (flow === 'scrolled') {
             // FIXME: vertical-rl only, not -lr
             this.setAttribute('dir', vertical ? 'rtl' : 'ltr')
-            this.style.padding = '0'
+            this.#top.style.padding = '0'
             const columnWidth = maxInlineSize
 
             this.heads = null