Give a dashboard the panel's own size, and put the dots on its grid

A dashboard now carries the canvas it is drawn for (canvas_width /
canvas_height, presets plus two numbers in the settings panel). Editor and
wall panel render that surface at its true pixel size and scale it to fit,
so a side panel opening changes only the scale — never the arrangement
being made. With the width and column count known the dot pitch is exact,
(width + gap) / columns by row height + gap, so a dot sits where every
widget corner snaps. The wall panel shows no dots.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01H7LwYgJfpkbLCTeiAf8U4A

backend/app/flow/dashboards.py

@@ -180,6 +180,12 @@ class DashboardDef(BaseModel):
     #: How many columns the grid is cut into, so a dashboard can be matched to
     #: the panel it will hang on.
     columns: int = Field(default=12, ge=1, le=48)
+    #: The panel this dashboard is drawn for, in CSS pixels. Both the editor
+    #: and the wall panel scale that surface to fit whatever room they have, so
+    #: an arrangement does not depend on the window it was made in. Zero means
+    #: "unset" and the client falls back to its default.
+    canvas_width: int = Field(default=1920, ge=0, le=7680)
+    canvas_height: int = Field(default=1080, ge=0, le=4320)
     pages: list[PageDef] = Field(default_factory=list)
     #: Bumped on every save; a save based on an older one is refused.
     version: int = 1

frontend/src/client/schemas.gen.ts

@@ -218,6 +218,20 @@ export const DashboardDef_InputSchema = {
             title: 'Columns',
             default: 12
         },
+        canvas_width: {
+            type: 'integer',
+            maximum: 7680,
+            minimum: 0,
+            title: 'Canvas Width',
+            default: 1920
+        },
+        canvas_height: {
+            type: 'integer',
+            maximum: 4320,
+            minimum: 0,
+            title: 'Canvas Height',
+            default: 1080
+        },
         pages: {
             items: {
                 '$ref': '#/components/schemas/PageDef-Input'
@@ -255,6 +269,20 @@ export const DashboardDef_OutputSchema = {
             title: 'Columns',
             default: 12
         },
+        canvas_width: {
+            type: 'integer',
+            maximum: 7680,
+            minimum: 0,
+            title: 'Canvas Width',
+            default: 1920
+        },
+        canvas_height: {
+            type: 'integer',
+            maximum: 4320,
+            minimum: 0,
+            title: 'Canvas Height',
+            default: 1080
+        },
         pages: {
             items: {
                 '$ref': '#/components/schemas/PageDef-Output'

frontend/src/client/types.gen.ts

@@ -83,6 +83,8 @@ export type DashboardDef_Input = {
     name: string;
     title?: string;
     columns?: number;
+    canvas_width?: number;
+    canvas_height?: number;
     pages?: Array<PageDef_Input>;
     version?: number;
 };
@@ -94,6 +96,8 @@ export type DashboardDef_Output = {
     name: string;
     title?: string;
     columns?: number;
+    canvas_width?: number;
+    canvas_height?: number;
     pages?: Array<PageDef_Output>;
     version?: number;
 };

frontend/src/components/Dashboard/DashboardEditor.tsx

@@ -9,8 +9,13 @@ import {
   Settings2,
 } from "lucide-react"
 import { motion } from "motion/react"
-import { useEffect, useRef, useState } from "react"
-import { GridLayout, type Layout, useContainerWidth } from "react-grid-layout"
+import { type CSSProperties, useEffect, useRef, useState } from "react"
+import {
+  GridLayout,
+  type Layout,
+  type Position,
+  setTransform,
+} from "react-grid-layout"
 import "react-grid-layout/css/styles.css"
 
 import {
@@ -39,6 +44,8 @@ import { slideUp, transitions } from "@/lib/motion"
 import { cn } from "@/lib/utils"
 import { handleError } from "@/utils"
 import {
+  CanvasSurface,
+  canvasOf,
   columnsOf,
   type Dashboard,
   DashboardView,
@@ -47,6 +54,7 @@ import {
   pagesOf,
   placement,
   ROW_HEIGHT,
+  rowsOf,
   sectionsOf,
   widgetsOf,
 } from "./DashboardView"
@@ -127,6 +135,20 @@ function layoutOf(widgets: WidgetDef[], columns: number): Layout {
   })
 }
 
+/**
+ * How the grid positions and drags items on a CSS-scaled surface.
+ *
+ * The library's own `createScaledStrategy` divides the drag delta by the scale
+ * but drops the container offset while doing it, so a widget jumps on pick-up.
+ * Leaving `calcDragPosition` unset keeps its parent-relative maths, which
+ * already divides by `scale` — the only thing that needed saying.
+ */
+const scaledStrategy = (scale: number) => ({
+  type: "transform" as const,
+  scale,
+  calcStyle: setTransform as (pos: Position) => CSSProperties,
+})
+
 const same = (a: Layout, b: Layout) =>
   a.length === b.length &&
   a.every((item, index) => {
@@ -204,7 +226,7 @@ export function DashboardEditor({
   const page = pages.find((candidate) => candidate.id === pageId) ?? pages[0]
   const section = page ? sectionsOf(page)[0] : undefined
   const widgets = section ? widgetsOf(section) : []
-  const { width, containerRef, mounted } = useContainerWidth()
+  const canvas = canvasOf(draft)
 
   const updateWidgets = (next: WidgetDef[]) => {
     if (!page || !section) return
@@ -293,26 +315,29 @@ export function DashboardEditor({
     <p className="text-sm text-muted-foreground">
       This dashboard has no pages yet.
     </p>
-  ) : !edit ? (
-    <DashboardView dashboard={draft} pageId={page.id} />
-  ) : widgets.length === 0 ? (
+  ) : edit && widgets.length === 0 ? (
     <p className="text-sm text-muted-foreground" data-testid="dashboard-empty">
       Nothing on this page yet. Add a widget from the bar below.
     </p>
   ) : (
-    <div ref={containerRef}>
-      {/* Measured first: laying out against a guessed width would place every
-          widget once and then move it. */}
-      {mounted ? (
+    <CanvasSurface dashboard={draft} dots={edit}>
+      {(scale) =>
+        !edit ? (
+          <DashboardView dashboard={draft} pageId={page.id} />
+        ) : (
           <GridLayout
-          width={width}
+            width={canvas.width}
             layout={layout}
             onLayoutChange={applyLayout}
+            positionStrategy={scaledStrategy(scale)}
             gridConfig={{
               cols: columns,
               rowHeight: ROW_HEIGHT,
               margin: [GRID_GAP, GRID_GAP],
               containerPadding: [0, 0],
+              // The canvas is the constraint: nothing may be dragged off the
+              // panel it is being drawn for.
+              maxRows: rowsOf(draft),
             }}
             // Only the header moves a widget, so a slider under the cursor still
             // slides and a switch still flips while the dashboard is being edited.
@@ -341,15 +366,16 @@ export function DashboardEditor({
               </div>
             ))}
           </GridLayout>
-      ) : null}
-    </div>
+        )
+      }
+    </CanvasSurface>
   )
 
   return (
     <>
       <div
         className={cn(
-          "dot-canvas absolute inset-0 overflow-y-auto px-4 pb-24 pt-20 transition-[padding] duration-200",
+          "absolute inset-0 overflow-hidden px-4 pb-24 pt-20 transition-[padding] duration-200",
           panelOpen && "md:pr-[27rem]",
         )}
         data-testid="dashboard-canvas"

frontend/src/components/Dashboard/DashboardView.tsx

@@ -1,3 +1,5 @@
+import { useEffect, useRef, useState } from "react"
+
 import type {
   DashboardDef_Output,
   PageDef_Output,
@@ -17,12 +19,27 @@ export const DEFAULT_COLUMNS = 12
 /** What a grid size setting may be set to; a panel is matched to one of these. */
 export const COLUMN_CHOICES = [6, 8, 12, 16, 24]
 
+/** The panel a dashboard is drawn for, if the document does not say. */
+export const DEFAULT_CANVAS = { width: 1920, height: 1080 }
+
+/** Panels worth a name; anything else is typed in as two numbers. */
+export const CANVAS_PRESETS = [
+  { label: '7" panel', width: 1024, height: 600 },
+  { label: '10" tablet', width: 1280, height: 800 },
+  { label: "Full HD", width: 1920, height: 1080 },
+  { label: '10" tablet, portrait', width: 800, height: 1280 },
+  { label: "Full HD, portrait", width: 1080, height: 1920 },
+]
+
 /** One grid row, in pixels — the unit widget heights are multiples of. */
 export const ROW_HEIGHT = 80
 
 /** The gap between widgets, in pixels. Matches the `gap-3` view mode uses. */
 export const GRID_GAP = 12
 
+/** Distance between two row origins — what a widget's `y` is counted in. */
+export const ROW_PITCH = ROW_HEIGHT + GRID_GAP
+
 /**
  * The generated client marks every list optional, because the server fills
  * them in. These three keep that from spreading through the components.
@@ -34,6 +51,82 @@ export const widgetsOf = (section: SectionDef_Output) => section.widgets ?? []
 export const columnsOf = (dashboard: Dashboard) =>
   dashboard.columns || DEFAULT_COLUMNS
 
+export const canvasOf = (dashboard: Dashboard) => ({
+  width: dashboard.canvas_width || DEFAULT_CANVAS.width,
+  height: dashboard.canvas_height || DEFAULT_CANVAS.height,
+})
+
+/** How many rows of the grid fit in the canvas; the rest is off the panel. */
+export const rowsOf = (dashboard: Dashboard) =>
+  Math.max(1, Math.floor((canvasOf(dashboard).height + GRID_GAP) / ROW_PITCH))
+
+/**
+ * The dashboard's own surface: exactly the panel's pixel size, scaled to fit
+ * whatever room is left around it.
+ *
+ * Scaling rather than reflowing is the point. A side panel opening, or a
+ * narrower screen, changes only the scale — the arrangement being designed,
+ * and the dot grid under it, stay the layout the panel will actually show.
+ */
+export function CanvasSurface({
+  dashboard,
+  dots,
+  children,
+}: {
+  dashboard: Dashboard
+  /** Draw the placement grid. A wall panel is not being arranged, so: no. */
+  dots?: boolean
+  children: (scale: number) => React.ReactNode
+}) {
+  const ref = useRef<HTMLDivElement>(null)
+  const [box, setBox] = useState({ width: 0, height: 0 })
+
+  useEffect(() => {
+    const element = ref.current
+    if (!element) return
+    const observer = new ResizeObserver(([entry]) =>
+      setBox({
+        width: entry.contentRect.width,
+        height: entry.contentRect.height,
+      }),
+    )
+    observer.observe(element)
+    return () => observer.disconnect()
+  }, [])
+
+  const { width, height } = canvasOf(dashboard)
+  const scale = Math.min(box.width / width, box.height / height)
+
+  return (
+    <div ref={ref} className="relative size-full overflow-hidden">
+      {/* Measured first: a guessed scale would place the whole panel once and
+          then move it. */}
+      {scale > 0 ? (
+        <div
+          className={cn("absolute overflow-hidden", dots && "dot-canvas")}
+          data-testid="canvas-surface"
+          style={
+            {
+              width,
+              height,
+              left: (box.width - width * scale) / 2,
+              top: (box.height - height * scale) / 2,
+              transform: `scale(${scale})`,
+              transformOrigin: "top left",
+              // One dot per cell corner. The column pitch the grid snaps to is
+              // (width + gap) / columns; a row is one row plus the gap.
+              "--dot-x": `${(width + GRID_GAP) / columnsOf(dashboard)}px`,
+              "--dot-y": `${ROW_PITCH}px`,
+            } as React.CSSProperties
+          }
+        >
+          {children(scale)}
+        </div>
+      ) : null}
+    </div>
+  )
+}
+
 export function placement(widget: WidgetDef): Placement {
   const layout = (widget.layout ?? {}) as Record<string, Placement>
   return layout.lg ?? layout.md ?? layout.sm ?? {}

frontend/src/components/Dashboard/dashboard.css

@@ -6,8 +6,9 @@
  * so nothing here touches the byte-identical token blocks.
  */
 
-/* The same dot grid the flow viewport paints, as plain CSS: a dashboard has no
-   zoom, so it needs none of React Flow's rescaling. */
+/* The placement grid, as plain CSS. One dot per cell corner: the surface hands
+   in the pitch its widgets actually snap to (`--dot-x` / `--dot-y`), and the
+   negative offset puts a dot centre on the grid's own origin. */
 .dot-canvas {
   background-color: var(--background);
   background-image: radial-gradient(
@@ -15,42 +16,34 @@
     color-mix(in srgb, var(--muted-foreground) 30%, transparent) 1.5px,
     transparent 0
   );
-  background-size: 24px 24px;
+  background-size: var(--dot-x, 24px) var(--dot-y, 24px);
+  background-position: -1px -1px;
 }
 
 /*
  * View mode's grid. Column count is per dashboard (`--widget-cols`), so a wall
- * panel can be matched to its own width. Below the large breakpoint the stored
- * placement is meaningless — three columns cannot hold a twelve-column
- * arrangement — so widgets stack full width and keep only their height.
+ * panel can be matched to its own width. There is no responsive fallback: the
+ * grid lives on a canvas of the panel's own pixel size, which is scaled to the
+ * viewport rather than reflowed into it.
  */
 .widget-grid {
   display: grid;
   gap: 0.75rem;
   grid-auto-rows: 5rem;
-  grid-template-columns: minmax(0, 1fr);
+  grid-template-columns: repeat(var(--widget-cols), minmax(0, 1fr));
 }
 
 .widget-cell {
+  grid-column: span var(--w);
   grid-row: span var(--h);
   min-width: 0;
 }
 
-@media (min-width: 64rem) {
-  .widget-grid {
-    grid-template-columns: repeat(var(--widget-cols), minmax(0, 1fr));
-  }
-
-  .widget-cell {
-    grid-column: span var(--w);
-  }
-
-  /* Only once something has actually been placed; an untouched dashboard has
+/* Only once something has actually been placed; an untouched dashboard has
    every widget at 0,0 and would pile up on one cell. */
-  .widget-grid[data-placed] .widget-cell {
+.widget-grid[data-placed] .widget-cell {
   grid-column: var(--x) / span var(--w);
   grid-row: var(--y) / span var(--h);
-  }
 }
 
 /*

frontend/src/components/Dashboard/panels.tsx

@@ -27,7 +27,13 @@ import {
   SelectValue,
 } from "@/components/ui/select"
 import { MAX_SERIES } from "./ChartWidget"
-import { COLUMN_CHOICES, columnsOf, type Dashboard } from "./DashboardView"
+import {
+  CANVAS_PRESETS,
+  COLUMN_CHOICES,
+  canvasOf,
+  columnsOf,
+  type Dashboard,
+} from "./DashboardView"
 import { messageCatalogQueryOptions } from "./queries"
 import {
   acceptsDtype,
@@ -314,12 +320,16 @@ export function WidgetPanel({
   )
 }
 
+/** Presets are matched on their size, so a custom one simply matches none. */
+const sizeKey = (size: { width: number; height: number }) =>
+  `${size.width}x${size.height}`
+
 /**
  * The dashboard's own settings, in the panel its widgets use.
  *
- * The grid size is the one that matters: a wall panel is a fixed width, and
- * twelve columns on a seven-inch screen is a different dashboard than twelve
- * on a television.
+ * The canvas is the one that matters: a wall panel is a fixed size, and twelve
+ * columns on a seven-inch screen is a different dashboard than twelve on a
+ * television.
  */
 export function DashboardPanel({
   open,
@@ -337,6 +347,7 @@ export function DashboardPanel({
   onClose: () => void
 }) {
   const [confirmOpen, setConfirmOpen] = useState(false)
+  const canvas = canvasOf(dashboard)
 
   return (
     <>
@@ -390,6 +401,65 @@ export function DashboardPanel({
             </p>
           </div>
 
+          <div className="grid gap-2">
+            <span className={PANEL_SECTION}>Canvas</span>
+            <Select
+              value={
+                CANVAS_PRESETS.some(
+                  (preset) => sizeKey(preset) === sizeKey(canvas),
+                )
+                  ? sizeKey(canvas)
+                  : ""
+              }
+              onValueChange={(value) => {
+                const preset = CANVAS_PRESETS.find(
+                  (candidate) => sizeKey(candidate) === value,
+                )
+                if (preset)
+                  onChange({
+                    canvas_width: preset.width,
+                    canvas_height: preset.height,
+                  })
+              }}
+            >
+              <SelectTrigger data-testid="dashboard-canvas-size">
+                <SelectValue placeholder="Custom" />
+              </SelectTrigger>
+              <SelectContent>
+                {CANVAS_PRESETS.map((preset) => (
+                  <SelectItem key={sizeKey(preset)} value={sizeKey(preset)}>
+                    {preset.label} — {preset.width}×{preset.height}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+            <div className="flex gap-2">
+              <Input
+                type="number"
+                aria-label="Canvas width"
+                data-testid="canvas-width"
+                value={canvas.width}
+                onChange={(event) =>
+                  onChange({ canvas_width: Number(event.target.value) || 0 })
+                }
+              />
+              <Input
+                type="number"
+                aria-label="Canvas height"
+                data-testid="canvas-height"
+                value={canvas.height}
+                onChange={(event) =>
+                  onChange({ canvas_height: Number(event.target.value) || 0 })
+                }
+              />
+            </div>
+            <p className="text-sm text-muted-foreground">
+              The panel this is drawn for, in pixels. Editing and viewing both
+              scale that surface to fit, so the arrangement is the same
+              everywhere.
+            </p>
+          </div>
+
           <div className="grid gap-2">
             <span className={PANEL_SECTION}>Contents</span>
             <p className="text-sm text-muted-foreground">

frontend/src/routes/view.$name.tsx

@@ -2,7 +2,10 @@ import { useQuery } from "@tanstack/react-query"
 import { createFileRoute, redirect } from "@tanstack/react-router"
 
 import type { Dashboard } from "@/components/Dashboard/DashboardView"
-import { DashboardView } from "@/components/Dashboard/DashboardView"
+import {
+  CanvasSurface,
+  DashboardView,
+} from "@/components/Dashboard/DashboardView"
 import { dashboardQueryOptions } from "@/components/Dashboard/queries"
 import { useFlowSocket } from "@/components/Flow/useFlowSocket"
 import { isLoggedIn } from "@/hooks/useAuth"
@@ -30,8 +33,14 @@ function PanelView() {
   const { data: dashboard } = useQuery(dashboardQueryOptions(name))
 
   return (
-    <main className="dot-canvas min-h-svh w-full overflow-y-auto p-4">
-      {dashboard ? <DashboardView dashboard={dashboard as Dashboard} /> : null}
+    <main className="h-svh w-full overflow-hidden p-4">
+      {dashboard ? (
+        // The panel's own surface, scaled to whatever screen it landed on. No
+        // dots: nothing is being arranged here.
+        <CanvasSurface dashboard={dashboard as Dashboard}>
+          {() => <DashboardView dashboard={dashboard as Dashboard} />}
+        </CanvasSurface>
+      ) : null}
     </main>
   )
 }