# Focus Context Window

> Dual overview and detail window with interactive brush area selector.

A shadcn/ui block from the [@paceui](https://paceui.com/?utm_source=shadcn.exchange) registry, listed on [shadcn.exchange](https://shadcn.exchange/r/paceui/tanstack-charts-focus-context-window).

- Page, with a live preview: https://shadcn.exchange/r/paceui/tanstack-charts-focus-context-window
- Screenshot: https://abzjhwgwpdpz7ua5.public.blob.vercel-storage.com/shots/paceui/tanstack-charts-focus-context-window-light-f35a6c9390adfdb7.png
- Registry item: https://paceui.com/r/tanstack-charts-focus-context-window.json
- Listed: 2026-10-21, source last changed 2026-10-21

## Install

```bash
npx shadcn@latest add https://shadcn.exchange/r/paceui/tanstack-charts-focus-context-window.json
```

Run it in a project that has shadcn/ui set up. It adds the files below and installs what they depend on.

## Dependencies

- npm packages: `@tanstack/charts`, `@tanstack/react-charts`, `d3-scale`
- Registry items: `card`

## Files

### `components/tanstack-charts/line/focus-context-window.tsx`

```tsx
import { type ChartPoint, defineChart, dot, lineY } from "@tanstack/charts";
import { brushX } from "@tanstack/charts/interaction/brush";
import { controlledSignal } from "@tanstack/charts/interaction/signal";
import { motion } from "@tanstack/charts/motion";
import { tooltip } from "@tanstack/charts/tooltip";
import { Chart } from "@tanstack/react-charts/core";
import { useMemo, useState } from "react";

import { scaleLinear, scaleUtc } from "d3-scale";
import { Maximize2 } from "lucide-react";

import { Card, CardContent, CardDescription, CardFooter, CardHeader, CardTitle } from "@/components/ui/card";

interface StockDatum {
    Date: Date;
    Close: number;
}

const motionRenderer = motion({
    initial: "always",
    transition: { type: "spring", stiffness: 170, damping: 18, mass: 1 },
});

function generateDemoData(): StockDatum[] {
    const results: StockDatum[] = [];
    let price = 120;

    for (let m = 0; m < 36; m++) {
        const date = new Date(Date.UTC(2022, m, 1));
        price += Math.sin(m * 0.3) * 5 + (Math.random() - 0.45) * 8;
        results.push({ Date: date, Close: Number(Math.max(80, price).toFixed(2)) });
    }

    return results;
}

function shadcnTooltipContent<TDatum>(points: readonly ChartPoint<TDatum>[]) {
    if (points.length === 0) return { title: "", rows: [] };
    const d = points[0].datum as StockDatum;
    if (!d || !d.Date) return { title: "", rows: [] };
    const dateObj = d.Date instanceof Date ? d.Date : new Date(d.Date);
    const titleStr = isNaN(dateObj.getTime())
        ? ""
        : dateObj.toLocaleDateString("en-US", { month: "short", year: "numeric", timeZone: "UTC" });
    return {
        title: titleStr,
        rows: [{ label: "Closing Price", value: `$${d.Close.toFixed(2)}`, color: "var(--chart-1)" }],
    };
}

export function FocusContextWindow() {
    const data = useMemo(() => generateDemoData(), []);

    const fullDates = useMemo(() => data.map((d) => d.Date), [data]);
    const fullDomain = useMemo(() => [fullDates[0], fullDates[fullDates.length - 1]], [fullDates]);

    const [range, setRange] = useState<{ start: Date; end: Date }>({
        start: fullDates[12],
        end: fullDates[24],
    });

    const filteredDetailData = useMemo(() => {
        const startTime = range.start instanceof Date ? range.start.getTime() : new Date(range.start).getTime();
        const endTime = range.end instanceof Date ? range.end.getTime() : new Date(range.end).getTime();
        return data.filter((d) => {
            const t = d.Date instanceof Date ? d.Date.getTime() : new Date(d.Date).getTime();
            return t >= startTime && t <= endTime;
        });
    }, [data, range]);

    const detailDefinition = useMemo(
        () =>
            defineChart(
                {
                    renderer: motionRenderer,
                    marks: [
                        lineY(filteredDetailData, {
                            id: "detail-line",
                            x: "Date",
                            y: "Close",
                            stroke: "var(--chart-1)",
                            strokeWidth: 2.5,
                        }),
                        dot(filteredDetailData, {
                            id: "detail-points",
                            x: "Date",
                            y: "Close",
                            fill: "var(--chart-1)",
                            r: 3.5,
                        }),
                    ],
                    scales: {
                        x: {
                            scale: scaleUtc().domain([
                                range.start instanceof Date ? range.start : new Date(range.start),
                                range.end instanceof Date ? range.end : new Date(range.end),
                            ]),
                            axis: { label: "Focus Zoomed Window" },
                        },
                        y: {
                            scale: scaleLinear,
                            grid: true,
                            axis: { label: "Stock Close ($)" },
                        },
                    },
                    margin: { top: 16, right: 24, bottom: 32, left: 45 },
                    theme: {
                        foreground: "var(--muted-foreground)",
                        grid: "var(--border)",
                        background: "transparent",
                    },
                },
                {
                    keyboard: true,
                    tooltip: {
                        use: tooltip,
                        className:
                            "font-sans shadow-none rounded-md bg-popover text-popover-foreground border p-2 text-xs",
                        anchor: "pointer",
                        placement: "auto",
                        content: (points) => shadcnTooltipContent(points),
                    },
                },
            ),
        [filteredDetailData, range],
    );

    const overviewDefinition = useMemo(
        () =>
            defineChart(
                {
                    renderer: motionRenderer,
                    marks: [
                        lineY(data, {
                            id: "overview-line",
                            x: "Date",
                            y: "Close",
                            stroke: "var(--chart-1)",
                            strokeWidth: 1.5,
                        }),
                    ],
                    scales: {
                        x: {
                            scale: scaleUtc().domain(fullDomain),
                            axis: {
                                ticks: {
                                    count: 4,
                                    format: (v: any) => {
                                        const dateObj = v instanceof Date ? v : new Date(v);
                                        return isNaN(dateObj.getTime())
                                            ? ""
                                            : dateObj.toLocaleDateString("en-US", { month: "short", timeZone: "UTC" });
                                    },
                                },
                            },
                        },
                        y: { scale: scaleLinear, axis: false },
                    },
                    controls: [
                        brushX({
                            id: "focus-window",
                            range: controlledSignal(range, (next: any) => {
                                if (!next) return;
                                setRange({
                                    start: next.start instanceof Date ? next.start : new Date(next.start),
                                    end: next.end instanceof Date ? next.end : new Date(next.end),
                                });
                            }),
                            values: fullDates,
                            ariaLabel: "Time window brush selector",
                            selectionStyle: {
                                fill: "var(--chart-1)",
                                fillOpacity: 0.2,
                                stroke: "var(--chart-1)",
                                strokeWidth: 1.5,
                            },
                            handleStyle: { fill: "var(--chart-1)", fillOpacity: 0.9 },
                        }),
                    ],
                    margin: { top: 8, right: 24, bottom: 20, left: 45 },
                    theme: {
                        foreground: "var(--muted-foreground)",
                        grid: "var(--border)",
                        background: "transparent",
                    },
                },
                { keyboard: false },
            ),
        [data, fullDates, fullDomain, range],
    );

    return (
        <Card className="w-full max-w-xl">
            <CardHeader>
                <CardTitle>Dual Focus + Context Brush Zoom Window</CardTitle>
                <CardDescription>
                    Drag and resize the overview brush region to pan and zoom detailed line series view
                </CardDescription>
            </CardHeader>
            <CardContent className="space-y-3">
                <div className="h-[180px] w-full">
                    <Chart
                        definition={detailDefinition}
                        renderer={motionRenderer}
                        height={180}
                        ariaLabel="Detail Focus Window View"
                    />
                </div>
                <div className="h-[75px] w-full">
                    <Chart
                        definition={overviewDefinition}
                        renderer={motionRenderer}
                        height={75}
                        ariaLabel="Overview Context Window View"
                    />
                </div>
            </CardContent>
            <CardFooter className="flex-col items-start gap-2 text-sm">
                <div className="flex items-center gap-2 leading-none font-medium">
                    Overview brush coordinates update detail zoom domain live{" "}
                    <Maximize2 className="h-4 w-4 text-emerald-500" />
                </div>
                <div className="text-muted-foreground leading-none">
                    `brushX` mark provides interactive handle dragging for smooth temporal pan/zoom
                </div>
            </CardFooter>
        </Card>
    );
}

export default FocusContextWindow;
```