separate components in different files

src/canvas.js

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+import React, {useRef, useEffect} from 'react';
+import qrcodegen from './third-party/qrcodegen';
+import { QRProps, DEFAULT_PROPS, MARGIN_SIZE, ERROR_LEVEL_MAP, generatePath, excavateModules, getImageSettings } from './helpers';
+
+
+// For canvas we're going to switch our drawing mode based on whether or not
+// the environment supports Path2D. We only need the constructor to be
+// supported, but Edge doesn't actually support the path (string) type
+// argument. Luckily it also doesn't support the addPath() method. We can
+// treat that as the same thing.
+const SUPPORTS_PATH2D = (function () {
+  try {
+    new Path2D().addPath(new Path2D());
+  } catch (e) {
+    return false;
+  }
+  return true;
+})();
+
+
+export default function QRCodeCanvas(props: QRProps) {
+  const _canvas = useRef<HTMLCanvasElement>(null);
+  const _image = useRef<HTMLImageElement>(null);
+
+  function update() {
+    const {value, size, level, bgColor, fgColor, includeMargin} = props;
+
+    if (_canvas.current != null) {
+      const canvas = _canvas.current;
+
+      const ctx = canvas.getContext('2d');
+      if (!ctx) {
+        return;
+      }
+
+      let cells = qrcodegen.QrCode.encodeText(
+        value,
+        ERROR_LEVEL_MAP[level]
+      ).getModules();
+
+      const margin = includeMargin ? MARGIN_SIZE : 0;
+      const numCells = cells.length + margin * 2;
+      const calculatedImageSettings = getImageSettings(props, cells);
+
+      const image = _image.current;
+      const haveImageToRender =
+        calculatedImageSettings != null &&
+        image !== null &&
+        image.complete &&
+        image.naturalHeight !== 0 &&
+        image.naturalWidth !== 0;
+
+      if (haveImageToRender) {
+        if (calculatedImageSettings.excavation != null) {
+          cells = excavateModules(cells, calculatedImageSettings.excavation);
+        }
+      }
+
+      // We're going to scale this so that the number of drawable units
+      // matches the number of cells. This avoids rounding issues, but does
+      // result in some potentially unwanted single pixel issues between
+      // blocks, only in environments that don't support Path2D.
+      const pixelRatio = window.devicePixelRatio || 1;
+      canvas.height = canvas.width = size * pixelRatio;
+      const scale = (size / numCells) * pixelRatio;
+      ctx.scale(scale, scale);
+
+      // Draw solid background, only paint dark modules.
+      ctx.fillStyle = bgColor;
+      ctx.fillRect(0, 0, numCells, numCells);
+
+      ctx.fillStyle = fgColor;
+      if (SUPPORTS_PATH2D) {
+        // $FlowFixMe: Path2D c'tor doesn't support args yet.
+        ctx.fill(new Path2D(generatePath(cells, margin)));
+      } else {
+        cells.forEach(function (row, rdx) {
+          row.forEach(function (cell, cdx) {
+            if (cell) {
+              ctx.fillRect(cdx + margin, rdx + margin, 1, 1);
+            }
+          });
+        });
+      }
+
+      if (haveImageToRender) {
+        ctx.drawImage(
+          image,
+          calculatedImageSettings.x + margin,
+          calculatedImageSettings.y + margin,
+          calculatedImageSettings.w,
+          calculatedImageSettings.h
+        );
+      }
+    }
+  }
+
+  useEffect(() => {
+    // Always update the canvas. It's cheap enough and we want to be correct
+    // with the current state.
+    update();
+  });
+
+  const {
+    value,
+    size,
+    level,
+    bgColor,
+    fgColor,
+    style,
+    includeMargin,
+    imageSettings,
+    ...otherProps
+  } = props;
+  const canvasStyle = {height: size, width: size, ...style};
+  let img = null;
+  let imgSrc = imageSettings?.src;
+  if (imgSrc != null) {
+    img = (
+      <img
+        src={imgSrc}
+        key={imgSrc}
+        style={{display: 'none'}}
+        onLoad={() => {
+          update();
+        }}
+        ref={_image}
+      />
+    );
+  }
+  return (
+    <>
+      <canvas
+        style={canvasStyle}
+        height={size}
+        width={size}
+        ref={_canvas}
+        {...otherProps}
+      />
+      {img}
+    </>
+  );
+}
+
+QRCodeCanvas.defaultProps = DEFAULT_PROPS;

src/helpers.js

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+import qrcodegen from './third-party/qrcodegen';
+import type {CSSProperties} from 'react';
+
+type Modules = ReturnType<qrcodegen.QrCode['getModules']>;
+type Excavation = {x: number; y: number; w: number; h: number};
+
+export const ERROR_LEVEL_MAP: {[index: string]: qrcodegen.QrCode.Ecc} = {
+  L: qrcodegen.QrCode.Ecc.LOW,
+  M: qrcodegen.QrCode.Ecc.MEDIUM,
+  Q: qrcodegen.QrCode.Ecc.QUARTILE,
+  H: qrcodegen.QrCode.Ecc.HIGH,
+};
+
+export type QRProps = {
+  value: string;
+  size: number;
+  // Should be a real enum, but doesn't seem to be compatible with real code.
+  level: string;
+  bgColor: string;
+  fgColor: string;
+  style?: CSSProperties;
+  includeMargin: boolean;
+  imageSettings?: {
+    src: string;
+    height: number;
+    width: number;
+    excavate: boolean;
+    x?: number;
+    y?: number;
+  };
+};
+
+export const DEFAULT_PROPS = {
+  size: 128,
+  level: 'L',
+  bgColor: '#FFFFFF',
+  fgColor: '#000000',
+  includeMargin: false,
+};
+
+export const MARGIN_SIZE = 4;
+
+// This is *very* rough estimate of max amount of QRCode allowed to be covered.
+// It is "wrong" in a lot of ways (area is a terrible way to estimate, it
+// really should be number of modules covered), but if for some reason we don't
+// get an explicit height or width, I'd rather default to something than throw.
+const DEFAULT_IMG_SCALE = 0.1;
+
+export function generatePath(modules: Modules, margin: number = 0): string {
+  const ops: Array<string> = [];
+  modules.forEach(function (row, y) {
+    let start: number | null = null;
+    row.forEach(function (cell, x) {
+      if (!cell && start !== null) {
+        // M0 0h7v1H0z injects the space with the move and drops the comma,
+        // saving a char per operation
+        ops.push(
+          `M${start + margin} ${y + margin}h${x - start}v1H${start + margin}z`
+        );
+        start = null;
+        return;
+      }
+
+      // end of row, clean up or skip
+      if (x === row.length - 1) {
+        if (!cell) {
+          // We would have closed the op above already so this can only mean
+          // 2+ light modules in a row.
+          return;
+        }
+        if (start === null) {
+          // Just a single dark module.
+          ops.push(`M${x + margin},${y + margin} h1v1H${x + margin}z`);
+        } else {
+          // Otherwise finish the current line.
+          ops.push(
+            `M${start + margin},${y + margin} h${x + 1 - start}v1H${
+              start + margin
+            }z`
+          );
+        }
+        return;
+      }
+
+      if (cell && start === null) {
+        start = x;
+      }
+    });
+  });
+  return ops.join('');
+}
+
+// We could just do this in generatePath, except that we want to support
+// non-Path2D canvas, so we need to keep it an explicit step.
+export function excavateModules(modules: Modules, excavation: Excavation): Modules {
+  return modules.slice().map((row, y) => {
+    if (y < excavation.y || y >= excavation.y + excavation.h) {
+      return row;
+    }
+    return row.map((cell, x) => {
+      if (x < excavation.x || x >= excavation.x + excavation.w) {
+        return cell;
+      }
+      return false;
+    });
+  });
+}
+
+export function getImageSettings(
+  props: QRProps,
+  cells: Modules
+): null | {
+  x: number;
+  y: number;
+  h: number;
+  w: number;
+  excavation: Excavation | null;
+} {
+  const {imageSettings, size, includeMargin} = props;
+  if (imageSettings == null) {
+    return null;
+  }
+  const margin = includeMargin ? MARGIN_SIZE : 0;
+  const numCells = cells.length + margin * 2;
+  const defaultSize = Math.floor(size * DEFAULT_IMG_SCALE);
+  const scale = numCells / size;
+  const w = (imageSettings.width || defaultSize) * scale;
+  const h = (imageSettings.height || defaultSize) * scale;
+  const x =
+    imageSettings.x == null
+      ? cells.length / 2 - w / 2
+      : imageSettings.x * scale;
+  const y =
+    imageSettings.y == null
+      ? cells.length / 2 - h / 2
+      : imageSettings.y * scale;
+
+  let excavation = null;
+  if (imageSettings.excavate) {
+    let floorX = Math.floor(x);
+    let floorY = Math.floor(y);
+    let ceilW = Math.ceil(w + x - floorX);
+    let ceilH = Math.ceil(h + y - floorY);
+    excavation = {x: floorX, y: floorY, w: ceilW, h: ceilH};
+  }
+
+  return {x, y, h, w, excavation};
+}