fork from https://github.com/mozilla/pdf.js.git

examples/image_decoders/jpeg_viewer.mjs

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+/* Copyright 2018 Mozilla Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+if (!pdfjsImageDecoders.JpegImage) {
+  // eslint-disable-next-line no-alert
+  alert("Please build the pdfjs-dist library using `gulp dist-install`");
+}
+
+const JPEG_IMAGE = "fish.jpg";
+
+const jpegCanvas = document.getElementById("jpegCanvas");
+const jpegCtx = jpegCanvas.getContext("2d");
+
+// Load the image data, and convert it to a Uint8Array.
+//
+const response = await fetch(JPEG_IMAGE);
+if (!response.ok) {
+  throw new Error(response.statusText);
+}
+const typedArrayImage = await response.bytes();
+
+// Parse the image data using `JpegImage`.
+//
+const jpegImage = new pdfjsImageDecoders.JpegImage();
+jpegImage.parse(typedArrayImage);
+
+const width = jpegImage.width,
+  height = jpegImage.height;
+const jpegData = jpegImage.getData({
+  width,
+  height,
+  forceRGB: true,
+});
+
+// Render the JPEG image on a <canvas>.
+//
+const imageData = jpegCtx.createImageData(width, height);
+const imageBytes = imageData.data;
+for (let j = 0, k = 0, jj = width * height * 4; j < jj; ) {
+  imageBytes[j++] = jpegData[k++];
+  imageBytes[j++] = jpegData[k++];
+  imageBytes[j++] = jpegData[k++];
+  imageBytes[j++] = 255;
+}
+jpegCanvas.width = width;
+jpegCanvas.height = height;
+jpegCtx.putImageData(imageData, 0, 0);