# 阿拉伯文和从右到左文字

> Fabric.js 从右到左文字的光标位置更准确：ShapedIText 按浏览器实际绘制的阿拉伯文和连字来测量。

Source: https://fabricjs-document-engine.jscrate.dev/zh/docs/guides/rtl-text
Last updated: 2026-10-02

Fabric.js 会单独测量每个字母，再把宽度加起来。但它绘制时会一次画出一串字母，字体会把它们连在一起：阿拉伯文字母会变成相连的形态，“ffi”也可能变成一个连字。于是在 Fabric.js 从右到左文字中，实际画出的行比测量的短，光标、选区和点击都会偏离字母（[fabric.js #4815](https://github.com/fabricjs/fabric.js/issues/4815)）。40px 的阿拉伯文，光标可能偏出两个字母。

## 试一试

```tsx
"use client";

import { IText } from "fabric";
import { ShapedIText } from "fabricjs-document-engine/text";
import { TextCursorInputIcon } from "lucide-react";
import { useTranslations } from "next-intl";
import { useEffect, useRef, useState } from "react";

import { DemoCanvas, DemoFrame, Status, Toolbar, ToolButton } from "./demo-ui";
import { PAGE, useFabricCanvas } from "./use-fabric-canvas";

const ARABIC = "مرحبا بالعالم العربي الجميل";
const FIRST_SPACE = [...ARABIC].indexOf(" ");

export default function ShapedTextDemo() {
  const t = useTranslations("demos");
  const { elementRef, canvas } = useFabricCanvas();
  const textsRef = useRef<{ plain: IText; shaped: IText } | null>(null);
  const [active, setActive] = useState<"plain" | "shaped" | null>(null);

  useEffect(() => {
    if (!canvas) return;
    const common = {
      fontSize: 34,
      fontFamily: "sans-serif",
      direction: "rtl",
      textAlign: "right",
      originX: "right",
      originY: "top",
      left: PAGE.width - 24,
      cursorColor: "#e11d48",
      cursorWidth: 3,
    } as const;
    const plain = new IText(ARABIC, { ...common, top: 50, fill: "#71717a" });
    const shaped = new ShapedIText(ARABIC, {
      ...common,
      top: 170,
      fill: "#0d0d0d",
    });
    textsRef.current = { plain, shaped };
    canvas.add(plain, shaped);
    canvas.requestRenderAll();
    return () => {
      canvas.remove(plain, shaped);
    };
  }, [canvas]);

  function placeCursor(which: "plain" | "shaped") {
    const texts = textsRef.current;
    if (!canvas || !texts) return;
    texts.plain.exitEditing();
    texts.shaped.exitEditing();
    const text = texts[which];
    canvas.setActiveObject(text);
    text.enterEditing();
    text.setSelectionStart(FIRST_SPACE);
    text.setSelectionEnd(FIRST_SPACE);
    canvas.requestRenderAll();
    setActive(which);
  }

  return (
    <DemoFrame>
      <DemoCanvas elementRef={elementRef} label={t("canvas")} />

      <Toolbar>
        <ToolButton
          icon={TextCursorInputIcon}
          label={t("shaped.plain")}
          primary={active === "plain"}
          disabled={!canvas}
          onClick={() => placeCursor("plain")}
        />
        <ToolButton
          icon={TextCursorInputIcon}
          label={t("shaped.shaped")}
          primary={active === "shaped"}
          disabled={!canvas}
          onClick={() => placeCursor("shaped")}
        />
      </Toolbar>

      <Status tone={active === "plain" ? "error" : active ? "ok" : "idle"}>
        {active ? t(`shaped.${active}Result`) : t("shaped.hint")}
      </Status>
    </DemoFrame>
  );
}
```

```tsx
import { Canvas } from "fabric";
import { useLayoutEffect, useRef, useState } from "react";

/**
 * The page every demo draws on. The document keeps this size; CSS scales the
 * canvas down to fit its card, so saved documents and exports never depend on
 * the screen.
 */
export const PAGE = { width: 480, height: 300 };

// Selection handles in the site's style. Fabric does not save these.
const SELECTION = {
  borderColor: "#6f00ff",
  borderScaleFactor: 1.5,
  borderOpacityWhenMoving: 0.5,
  cornerStyle: "circle",
  cornerSize: 11,
  cornerColor: "#ffffff",
  cornerStrokeColor: "#6f00ff",
  transparentCorners: false,
} as const;

export function styleSelection(canvas: Canvas) {
  canvas.set({
    selectionColor: "rgba(111, 0, 255, 0.06)",
    selectionBorderColor: "#6f00ff",
    selectionLineWidth: 1,
  });
  const style = () => canvas.getActiveObject()?.set(SELECTION);
  canvas.on("selection:created", style);
  canvas.on("selection:updated", style);
}

/**
 * Creates a Fabric.js canvas once the `<canvas>` element exists, and disposes
 * it on unmount. The engine is created from the returned `canvas`.
 */
export function useFabricCanvas({ width, height } = PAGE) {
  const elementRef = useRef<HTMLCanvasElement>(null);
  const [canvas, setCanvas] = useState<Canvas | null>(null);

  // A layout effect creates the canvas before the first paint.
  useLayoutEffect(() => {
    const created = new Canvas(elementRef.current!, {
      width,
      height,
      backgroundColor: "#ffffff",
    });
    styleSelection(created);
    setCanvas(created);

    return () => {
      // Dispose after the engine's own cleanup, so its last recovery copy
      // still sees the objects.
      setTimeout(() => created.dispose().catch(() => undefined));
    };
  }, [width, height]);

  return { elementRef, canvas };
}
```

```tsx
import { Circle, type FabricObject, Rect, Triangle } from "fabric";
import type { LucideIcon } from "lucide-react";

import { cn } from "@/lib/utils";

import { PAGE } from "./use-fabric-canvas";

export const COLORS = ["#f2836f", "#5fe6c4", "#7ad9ec", "#6f00ff", "#ffd666"];

// Demo shapes are placed by their top-left corner, like a design tool.
const CORNER = { originX: "left", originY: "top" } as const;

/** A new shape at a random spot on the page. */
export function newShape(kind: "square" | "circle", fill?: string) {
  const left = 40 + Math.random() * (PAGE.width - 160);
  const top = 30 + Math.random() * (PAGE.height - 120);
  const color = fill ?? COLORS[Math.floor(Math.random() * COLORS.length)];
  return kind === "square"
    ? new Rect({
        ...CORNER,
        left,
        top,
        width: 88,
        height: 64,
        rx: 10,
        ry: 10,
        fill: color,
      })
    : new Circle({ ...CORNER, left, top, radius: 34, fill: color });
}

/** A small composed drawing, so no demo starts on an empty page. */
export function seedShapes(): FabricObject[] {
  return [
    new Rect({
      ...CORNER,
      left: 48,
      top: 56,
      width: 176,
      height: 124,
      rx: 16,
      ry: 16,
      fill: COLORS[4],
    }),
    new Circle({ ...CORNER, left: 268, top: 44, radius: 58, fill: COLORS[0] }),
    new Rect({
      ...CORNER,
      left: 256,
      top: 196,
      width: 176,
      height: 52,
      rx: 26,
      ry: 26,
      fill: COLORS[1],
    }),
    new Triangle({
      ...CORNER,
      left: 96,
      top: 196,
      width: 72,
      height: 60,
      fill: COLORS[3],
    }),
  ];
}

export function DemoFrame({
  className,
  ...props
}: React.ComponentProps<"div">) {
  return (
    <div
      className={cn(
        "flex w-full max-w-md flex-col gap-3 text-left outline-none",
        className
      )}
      {...props}
    />
  );
}

/**
 * Scales the fixed-size Fabric canvas to the frame's width. The rules are
 * `!important` because Fabric writes its sizes as inline styles.
 */
export function DemoCanvas({
  elementRef,
  label,
  page = PAGE,
  children,
}: {
  elementRef: React.Ref<HTMLCanvasElement>;
  label: string;
  page?: { width: number; height: number };
  children?: React.ReactNode;
}) {
  return (
    <div
      className="relative overflow-hidden rounded-lg border bg-white shadow-xs [&_.canvas-container]:aspect-(--page)! [&_.canvas-container]:h-auto! [&_.canvas-container]:w-full! [&_canvas]:h-full! [&_canvas]:w-full!"
      style={
        { "--page": `${page.width} / ${page.height}` } as React.CSSProperties
      }
    >
      <div>
        <canvas ref={elementRef} aria-label={label} />
      </div>
      {children}
    </div>
  );
}

export function Toolbar({ className, ...props }: React.ComponentProps<"div">) {
  return (
    <div
      className={cn("flex flex-wrap items-center gap-1.5", className)}
      {...props}
    />
  );
}

export function ToolButton({
  icon: Icon,
  label,
  iconOnly = false,
  primary = false,
  className,
  ...props
}: React.ComponentProps<"button"> & {
  icon: LucideIcon;
  label: string;
  iconOnly?: boolean;
  primary?: boolean;
}) {
  return (
    <button
      type="button"
      title={label}
      aria-label={iconOnly ? label : undefined}
      className={cn(
        "inline-flex h-8 min-w-0 items-center justify-center gap-1.5 rounded-md border px-2.5 text-[13px] font-medium whitespace-nowrap transition-colors disabled:pointer-events-none disabled:opacity-40 [&_svg]:size-3.5 [&_svg]:shrink-0",
        primary
          ? "border-transparent bg-foreground text-background hover:bg-foreground/85"
          : "bg-background hover:bg-muted",
        iconOnly && "w-8 px-0",
        className
      )}
      {...props}
    >
      <Icon aria-hidden />
      {!iconOnly && <span className="truncate">{label}</span>}
    </button>
  );
}

const TONES = {
  idle: "bg-zinc-400",
  busy: "bg-amber-400",
  ok: "bg-emerald-500",
  error: "bg-red-500",
};

/** One line of status text. Its height never changes, so the card never jumps. */
export function Status({
  tone = "idle",
  children,
}: {
  tone?: keyof typeof TONES;
  children: React.ReactNode;
}) {
  return (
    <p
      role="status"
      className="flex h-5 min-w-0 items-center gap-2 text-[13px] text-muted-foreground"
    >
      <span
        aria-hidden
        className={cn("size-1.5 shrink-0 rounded-full", TONES[tone])}
      />
      <span className="truncate">{children}</span>
    </p>
  );
}
```

两行是同样的阿拉伯文。按钮会把光标放在第一个单词之后。

## 使用按字形测量的类

```ts
import {
  ShapedIText,
  ShapedTextbox,
  textObjects,
} from "fabricjs-document-engine/text";

const engine = createDocumentEngine({ canvas, customObjects: textObjects });

canvas.add(
  new ShapedIText("مرحبا بالعالم", {
    direction: "rtl",
    textAlign: "right",
    fontSize: 36,
  })
);
```

`ShapedIText` 和 `ShapedTextbox` 按浏览器实际排版的文字逐词测量每个位置，并缓存结果。输入、选择、点击、复制和粘贴和 IText、Textbox 一样。

- Fabric.js 从右到左文字仍然使用 `direction: "rtl"`。
- 拉丁字体中的连字，例如 “fi” 和 “ffi”，也会得到同样的修正。
- 有字间距（`charSpacing`）、`justify` 或沿路径排列的文字，Fabric 本来就逐个字母绘制，测量已经准确，所以保持不变。

## 在 BoundedTextbox 中

```ts
new BoundedTextbox(arabicText, { width: 260, direction: "rtl", shaping: true });
```

`shaping: true` 还会让换行跟随相连的字母。见[文本框宽度](https://fabricjs-document-engine.jscrate.dev/zh/docs/guides/textbox-width)。

测量函数列在[文字 API](https://fabricjs-document-engine.jscrate.dev/zh/docs/api/text-api)里，可以用在你自己的 Fabric.js 从右到左文字类中。