refactor: separate elements logic into a standalone package (#9285)

packages/element/src/textMeasurements.ts

@@ -0,0 +1,227 @@
+import {
+  BOUND_TEXT_PADDING,
+  DEFAULT_FONT_SIZE,
+  DEFAULT_FONT_FAMILY,
+  getFontString,
+  isTestEnv,
+  normalizeEOL,
+} from "@excalidraw/common";
+
+import type { FontString, ExcalidrawTextElement } from "./types";
+
+export const measureText = (
+  text: string,
+  font: FontString,
+  lineHeight: ExcalidrawTextElement["lineHeight"],
+) => {
+  const _text = text
+    .split("\n")
+    // replace empty lines with single space because leading/trailing empty
+    // lines would be stripped from computation
+    .map((x) => x || " ")
+    .join("\n");
+  const fontSize = parseFloat(font);
+  const height = getTextHeight(_text, fontSize, lineHeight);
+  const width = getTextWidth(_text, font);
+  return { width, height };
+};
+
+const DUMMY_TEXT = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".toLocaleUpperCase();
+
+// FIXME rename to getApproxMinContainerWidth
+export const getApproxMinLineWidth = (
+  font: FontString,
+  lineHeight: ExcalidrawTextElement["lineHeight"],
+) => {
+  const maxCharWidth = getMaxCharWidth(font);
+  if (maxCharWidth === 0) {
+    return (
+      measureText(DUMMY_TEXT.split("").join("\n"), font, lineHeight).width +
+      BOUND_TEXT_PADDING * 2
+    );
+  }
+  return maxCharWidth + BOUND_TEXT_PADDING * 2;
+};
+
+export const getMinTextElementWidth = (
+  font: FontString,
+  lineHeight: ExcalidrawTextElement["lineHeight"],
+) => {
+  return measureText("", font, lineHeight).width + BOUND_TEXT_PADDING * 2;
+};
+
+export const isMeasureTextSupported = () => {
+  const width = getTextWidth(
+    DUMMY_TEXT,
+    getFontString({
+      fontSize: DEFAULT_FONT_SIZE,
+      fontFamily: DEFAULT_FONT_FAMILY,
+    }),
+  );
+  return width > 0;
+};
+
+export const normalizeText = (text: string) => {
+  return (
+    normalizeEOL(text)
+      // replace tabs with spaces so they render and measure correctly
+      .replace(/\t/g, "        ")
+  );
+};
+
+const splitIntoLines = (text: string) => {
+  return normalizeText(text).split("\n");
+};
+
+/**
+ * To get unitless line-height (if unknown) we can calculate it by dividing
+ * height-per-line by fontSize.
+ */
+export const detectLineHeight = (textElement: ExcalidrawTextElement) => {
+  const lineCount = splitIntoLines(textElement.text).length;
+  return (textElement.height /
+    lineCount /
+    textElement.fontSize) as ExcalidrawTextElement["lineHeight"];
+};
+
+/**
+ * We calculate the line height from the font size and the unitless line height,
+ * aligning with the W3C spec.
+ */
+export const getLineHeightInPx = (
+  fontSize: ExcalidrawTextElement["fontSize"],
+  lineHeight: ExcalidrawTextElement["lineHeight"],
+) => {
+  return fontSize * lineHeight;
+};
+
+// FIXME rename to getApproxMinContainerHeight
+export const getApproxMinLineHeight = (
+  fontSize: ExcalidrawTextElement["fontSize"],
+  lineHeight: ExcalidrawTextElement["lineHeight"],
+) => {
+  return getLineHeightInPx(fontSize, lineHeight) + BOUND_TEXT_PADDING * 2;
+};
+
+let textMetricsProvider: TextMetricsProvider | undefined;
+
+/**
+ * Set a custom text metrics provider.
+ *
+ * Useful for overriding the width calculation algorithm where canvas API is not available / desired.
+ */
+export const setCustomTextMetricsProvider = (provider: TextMetricsProvider) => {
+  textMetricsProvider = provider;
+};
+
+export interface TextMetricsProvider {
+  getLineWidth(text: string, fontString: FontString): number;
+}
+
+class CanvasTextMetricsProvider implements TextMetricsProvider {
+  private canvas: HTMLCanvasElement;
+
+  constructor() {
+    this.canvas = document.createElement("canvas");
+  }
+
+  /**
+   * We need to use the advance width as that's the closest thing to the browser wrapping algo, hence using it for:
+   * - text wrapping
+   * - wysiwyg editor (+padding)
+   *
+   * > The advance width is the distance between the glyph's initial pen position and the next glyph's initial pen position.
+   */
+  public getLineWidth(text: string, fontString: FontString): number {
+    const context = this.canvas.getContext("2d")!;
+    context.font = fontString;
+    const metrics = context.measureText(text);
+    const advanceWidth = metrics.width;
+
+    // since in test env the canvas measureText algo
+    // doesn't measure text and instead just returns number of
+    // characters hence we assume that each letteris 10px
+    if (isTestEnv()) {
+      return advanceWidth * 10;
+    }
+
+    return advanceWidth;
+  }
+}
+
+export const getLineWidth = (text: string, font: FontString) => {
+  if (!textMetricsProvider) {
+    textMetricsProvider = new CanvasTextMetricsProvider();
+  }
+
+  return textMetricsProvider.getLineWidth(text, font);
+};
+
+export const getTextWidth = (text: string, font: FontString) => {
+  const lines = splitIntoLines(text);
+  let width = 0;
+  lines.forEach((line) => {
+    width = Math.max(width, getLineWidth(line, font));
+  });
+
+  return width;
+};
+
+export const getTextHeight = (
+  text: string,
+  fontSize: number,
+  lineHeight: ExcalidrawTextElement["lineHeight"],
+) => {
+  const lineCount = splitIntoLines(text).length;
+  return getLineHeightInPx(fontSize, lineHeight) * lineCount;
+};
+
+export const charWidth = (() => {
+  const cachedCharWidth: { [key: FontString]: Array<number> } = {};
+
+  const calculate = (char: string, font: FontString) => {
+    const unicode = char.charCodeAt(0);
+    if (!cachedCharWidth[font]) {
+      cachedCharWidth[font] = [];
+    }
+    if (!cachedCharWidth[font][unicode]) {
+      const width = getLineWidth(char, font);
+      cachedCharWidth[font][unicode] = width;
+    }
+
+    return cachedCharWidth[font][unicode];
+  };
+
+  const getCache = (font: FontString) => {
+    return cachedCharWidth[font];
+  };
+
+  const clearCache = (font: FontString) => {
+    cachedCharWidth[font] = [];
+  };
+
+  return {
+    calculate,
+    getCache,
+    clearCache,
+  };
+})();
+
+export const getMinCharWidth = (font: FontString) => {
+  const cache = charWidth.getCache(font);
+  if (!cache) {
+    return 0;
+  }
+  const cacheWithOutEmpty = cache.filter((val) => val !== undefined);
+
+  return Math.min(...cacheWithOutEmpty);
+};
+
+export const getMaxCharWidth = (font: FontString) => {
+  const cache = charWidth.getCache(font);
+  if (!cache) {
+    return 0;
+  }
+  const cacheWithOutEmpty = cache.filter((val) => val !== undefined);
+  return Math.max(...cacheWithOutEmpty);
+};