make it configurable whether rgba image buffer should be reused / ove…

…rwritten

README.md

@@ -64,6 +64,7 @@ This data is in the same form as the [`ImageData`](https://developer.mozilla.org
 - `height` - The height of the image you wish to decode.
 - `options` (optional) - Additional options.
   - `inversionAttempts` - (`attemptBoth` (default), `dontInvert`, `onlyInvert`, or `invertFirst`) - Should jsQR attempt to invert the image to find QR codes with white modules on black backgrounds instead of the black modules on white background. This option defaults to `attemptBoth` for backwards compatibility but causes a ~50% performance hit, and will probably be default to `dontInvert` in future versions.
+  - `canOverwriteImage` - (`true` (default) or `false`) - Specifies whether the image data can be overwritten for performance improvements or whether it should be kept untouched. If `true` the image buffer will be used internally to reduce additional memory allocation.
 
 ### Return value
 If a QR is able to be decoded the library will return an object with the following keys.

src/binarizer/index.ts

@@ -27,17 +27,21 @@ class Matrix {
   }
 }
 
-export function binarize(data: Uint8ClampedArray, width: number, height: number, returnInverted: boolean) {
+export function binarize(data: Uint8ClampedArray, width: number, height: number, returnInverted: boolean,
+                         canOverwriteImage: boolean) {
   const pixelCount = width * height;
   if (data.length !== pixelCount * 4) {
     throw new Error("Malformed data passed to binarizer.");
   }
   // assign the greyscale and binary image within the rgba buffer as the rgba image will not be needed after conversion
   let bufferOffset = 0;
   // Convert image to greyscale
-  const greyScaleBuffer = new Uint8ClampedArray(data.buffer, bufferOffset, pixelCount);
-  bufferOffset += pixelCount;
-  const greyscalePixels = new Matrix(width, height, greyScaleBuffer);
+  let greyscaleBuffer: Uint8ClampedArray;
+  if (canOverwriteImage) {
+    greyscaleBuffer = new Uint8ClampedArray(data.buffer, bufferOffset, pixelCount);
+    bufferOffset += pixelCount;
+  }
+  const greyscalePixels = new Matrix(width, height, greyscaleBuffer);
   for (let y = 0; y < height; y++) {
     for (let x = 0; x < width; x++) {
       const pixelPosition = (y * width + x) * 4;
@@ -51,8 +55,11 @@ export function binarize(data: Uint8ClampedArray, width: number, height: number,
   const verticalRegionCount = Math.ceil(height / REGION_SIZE);
   const blackPointsCount = horizontalRegionCount * verticalRegionCount;
 
-  const blackPointsBuffer = new Uint8ClampedArray(data.buffer, bufferOffset, blackPointsCount);
-  bufferOffset += blackPointsCount;
+  let blackPointsBuffer: Uint8ClampedArray;
+  if (canOverwriteImage) {
+    blackPointsBuffer = new Uint8ClampedArray(data.buffer, bufferOffset, blackPointsCount);
+    bufferOffset += blackPointsCount;
+  }
   const blackPoints = new Matrix(horizontalRegionCount, verticalRegionCount, blackPointsBuffer);
   for (let verticalRegion = 0; verticalRegion < verticalRegionCount; verticalRegion++) {
     for (let hortizontalRegion = 0; hortizontalRegion < horizontalRegionCount; hortizontalRegion++) {
@@ -100,13 +107,23 @@ export function binarize(data: Uint8ClampedArray, width: number, height: number,
     }
   }
 
-  const binarizedBuffer = new Uint8ClampedArray(data.buffer, bufferOffset, pixelCount);
-  bufferOffset += binarizedBuffer.byteLength;
-  const binarized = new BitMatrix(binarizedBuffer, width);
+  let binarized: BitMatrix;
+  if (canOverwriteImage) {
+    const binarizedBuffer = new Uint8ClampedArray(data.buffer, bufferOffset, pixelCount);
+    bufferOffset += pixelCount;
+    binarized = new BitMatrix(binarizedBuffer, width);
+  } else {
+    binarized = BitMatrix.createEmpty(width, height);
+  }
+
   let inverted: BitMatrix = null;
   if (returnInverted) {
-    const invertedBuffer = new Uint8ClampedArray(data.buffer, bufferOffset, pixelCount);
-    inverted = new BitMatrix(invertedBuffer, width);
+    if (canOverwriteImage) {
+      const invertedBuffer = new Uint8ClampedArray(data.buffer, bufferOffset, pixelCount);
+      inverted = new BitMatrix(invertedBuffer, width);
+    } else {
+      inverted = BitMatrix.createEmpty(width, height);
+    }
   }
 
   for (let verticalRegion = 0; verticalRegion < verticalRegionCount; verticalRegion++) {

src/index.ts

@@ -56,10 +56,12 @@ function scan(matrix: BitMatrix): QRCode | null {
 
 export interface Options {
   inversionAttempts?: "dontInvert" | "onlyInvert" | "attemptBoth" | "invertFirst";
+  canOverwriteImage?: boolean;
 }
 
 const defaultOptions: Options = {
   inversionAttempts: "attemptBoth",
+  canOverwriteImage: true,
 };
 
 function jsQR(data: Uint8ClampedArray, width: number, height: number, providedOptions: Options = {}): QRCode | null {
@@ -71,7 +73,7 @@ function jsQR(data: Uint8ClampedArray, width: number, height: number, providedOp
 
   const shouldInvert = options.inversionAttempts === "attemptBoth" || options.inversionAttempts === "invertFirst";
   const tryInvertedFirst = options.inversionAttempts === "onlyInvert" || options.inversionAttempts === "invertFirst";
-  const {binarized, inverted} = binarize(data, width, height, shouldInvert);
+  const {binarized, inverted} = binarize(data, width, height, shouldInvert, options.canOverwriteImage);
   let result = scan(tryInvertedFirst ? inverted : binarized);
   if (!result && (options.inversionAttempts === "attemptBoth" || options.inversionAttempts === "invertFirst")) {
     result = scan(tryInvertedFirst ? binarized : inverted);