implements page-numbers-plan
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import { degrees, type PDFFont, type PDFPage, type RGB } from 'pdf-lib';
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import { getPositionCoords, type OverlayPosition } from './pdf-overlay';
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const DEFAULT_MARGIN = 20;
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const DEFAULT_PADDING = 8;
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const DEFAULT_MIN_SIZE = 4;
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const DEFAULT_BORDER_WIDTH = 2;
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/** Baseline nudge used by the framed text stamps so glyphs sit inside the border. */
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const BASELINE_OFFSET_RATIO = 0.2;
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const DEFAULT_TOO_LONG_MESSAGE =
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'Der Text ist für mindestens eine Seite zu lang. Kürzen Sie den Text.';
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export type TextOverlayOptions = {
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font: PDFFont;
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text: string;
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size: number;
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color: RGB;
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position: OverlayPosition;
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/** Distance between the mark and the page edge in points. */
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margin?: number;
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/** Inner box padding; use `0` for a frameless, anchor-aligned mark. */
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padding?: number;
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framed?: boolean;
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borderWidth?: number;
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/** Additional counter-clockwise rotation of the mark in degrees. */
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rotation?: number;
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/** Font size floor while shrinking to fit the page. */
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minSize?: number;
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/**
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* Place the mark on rotated scans (`/Rotate 90`, `180`, `270`) where it is
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* visible instead of sideways. Opt-in so existing tools keep their output.
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*/
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compensatePageRotation?: boolean;
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tooLongMessage?: string;
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};
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type TextBox = {
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size: number;
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textHeight: number;
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boxWidth: number;
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boxHeight: number;
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};
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const measureText = (font: PDFFont, text: string, size: number) => {
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try {
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return { width: font.widthOfTextAtSize(text, size), height: font.heightAtSize(size) };
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} catch {
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throw new Error(
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'Der Text enthält Zeichen, die nicht dargestellt werden können. Entfernen Sie z. B. Emoji.'
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);
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}
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};
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const fitTextToPage = (
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font: PDFFont,
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text: string,
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requestedSize: number,
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pageWidth: number,
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pageHeight: number,
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margin: number,
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padding: number,
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minSize: number,
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tooLongMessage: string
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): TextBox => {
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const availableWidth = pageWidth - margin * 2;
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const availableHeight = pageHeight - margin * 2;
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let size = requestedSize;
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let metrics = measureText(font, text, size);
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while (
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size > minSize &&
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(metrics.width + padding * 2 > availableWidth || metrics.height + padding * 2 > availableHeight)
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) {
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size = Math.max(minSize, size - 0.5);
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metrics = measureText(font, text, size);
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}
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if (
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metrics.width + padding * 2 > availableWidth ||
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metrics.height + padding * 2 > availableHeight
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) {
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throw new Error(tooLongMessage);
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}
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return {
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size,
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textHeight: metrics.height,
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boxWidth: metrics.width + padding * 2,
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boxHeight: metrics.height + padding * 2
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};
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};
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/**
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* Lower-left corner for a (possibly rotated) box inside the given page size.
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* The bounding box of the rotated mark is aligned to the requested position, so
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* tilted text never crosses the page edge.
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*/
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export const getRotatedBoxPlacement = (
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pageWidth: number,
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pageHeight: number,
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boxWidth: number,
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boxHeight: number,
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position: OverlayPosition,
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angle: number,
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margin = DEFAULT_MARGIN
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) => {
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const radians = (angle * Math.PI) / 180;
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const cosine = Math.cos(radians);
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const sine = Math.sin(radians);
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const rotatedCorners = [
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{ x: 0, y: 0 },
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{ x: boxWidth * cosine, y: boxWidth * sine },
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{ x: -boxHeight * sine, y: boxHeight * cosine },
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{
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x: boxWidth * cosine - boxHeight * sine,
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y: boxWidth * sine + boxHeight * cosine
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}
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];
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const minX = Math.min(...rotatedCorners.map((corner) => corner.x));
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const maxX = Math.max(...rotatedCorners.map((corner) => corner.x));
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const minY = Math.min(...rotatedCorners.map((corner) => corner.y));
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const maxY = Math.max(...rotatedCorners.map((corner) => corner.y));
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const boundingCoordinates = getPositionCoords(
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pageWidth,
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pageHeight,
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maxX - minX,
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maxY - minY,
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position,
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margin
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);
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return {
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x: boundingCoordinates.x - minX,
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y: boundingCoordinates.y - minY,
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cosine,
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sine
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};
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};
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/** Normalised page rotation; anything that is not a multiple of 90 is ignored. */
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const getPageRotation = (page: PDFPage): number => {
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const angle = Math.round(page.getRotation().angle / 90) * 90;
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return ((angle % 360) + 360) % 360;
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};
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/** Displayed page size after applying `/Rotate`. */
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const getVisualPageSize = (pageWidth: number, pageHeight: number, pageRotation: number) =>
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pageRotation % 180 === 0
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? { width: pageWidth, height: pageHeight }
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: { width: pageHeight, height: pageWidth };
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/**
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* Maps a point on the displayed page back into default user space. Viewers
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* rotate page content clockwise by `/Rotate`, so this is the inverse rotation
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* that keeps a mark at the requested visual position.
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*/
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const toUserSpace = (
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point: { x: number; y: number },
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pageWidth: number,
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pageHeight: number,
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pageRotation: number
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) => {
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switch (pageRotation) {
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case 90:
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return { x: pageWidth - point.y, y: point.x };
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case 180:
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return { x: pageWidth - point.x, y: pageHeight - point.y };
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case 270:
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return { x: point.y, y: pageHeight - point.x };
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default:
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return point;
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}
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};
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/**
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* Draws a single line of text (optionally framed) at one of the standard
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* positions. Shrinks the font to fit the page and throws a German error instead
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* of clipping.
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*/
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export const drawTextOverlay = (page: PDFPage, options: TextOverlayOptions): void => {
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const {
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font,
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text,
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size,
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color,
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position,
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margin = DEFAULT_MARGIN,
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padding = DEFAULT_PADDING,
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framed = false,
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borderWidth = DEFAULT_BORDER_WIDTH,
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rotation = 0,
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minSize = DEFAULT_MIN_SIZE,
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compensatePageRotation = false,
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tooLongMessage = DEFAULT_TOO_LONG_MESSAGE
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} = options;
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const { width, height } = page.getSize();
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const pageRotation = compensatePageRotation ? getPageRotation(page) : 0;
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const visual = getVisualPageSize(width, height, pageRotation);
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const box = fitTextToPage(
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font,
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text,
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size,
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visual.width,
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visual.height,
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margin,
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padding,
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minSize,
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tooLongMessage
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);
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const placement = getRotatedBoxPlacement(
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visual.width,
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visual.height,
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box.boxWidth,
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box.boxHeight,
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position,
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rotation,
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margin
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);
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const origin = toUserSpace({ x: placement.x, y: placement.y }, width, height, pageRotation);
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const angle = rotation + pageRotation;
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const radians = (angle * Math.PI) / 180;
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const cosine = Math.cos(radians);
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const sine = Math.sin(radians);
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const offsetX = padding;
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const offsetY = padding + box.textHeight * BASELINE_OFFSET_RATIO;
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if (framed) {
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page.drawRectangle({
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x: origin.x,
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y: origin.y,
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width: box.boxWidth,
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height: box.boxHeight,
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borderColor: color,
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borderWidth,
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rotate: degrees(angle)
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});
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}
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page.drawText(text, {
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x: origin.x + offsetX * cosine - offsetY * sine,
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y: origin.y + offsetX * sine + offsetY * cosine,
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size: box.size,
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font,
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color,
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rotate: degrees(angle)
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});
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};
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