Handle the case where all the image data are in the alpha channel (bug 1975719)

and add an error message in case where there is no data in the image.

l10n/en-US/viewer.ftl

@@ -614,6 +614,8 @@ pdfjs-editor-add-signature-save-checkbox = Save signature
 pdfjs-editor-add-signature-save-warning-message = You’ve reached the limit of 5 saved signatures. Remove one to save more.
 pdfjs-editor-add-signature-image-upload-error-title = Couldn’t upload image
 pdfjs-editor-add-signature-image-upload-error-description = Check your network connection or try another image.
+pdfjs-editor-add-signature-image-no-data-error-title = Can’t convert this image into a signature
+pdfjs-editor-add-signature-image-no-data-error-description = Please try uploading a different image.
 pdfjs-editor-add-signature-error-close-button = Close
 
 ## Dialog buttons

src/display/editor/drawers/signaturedraw.js

@@ -366,21 +366,12 @@ class SignatureExtractor {
     let max = -Infinity;
     let min = Infinity;
     for (let i = 0, ii = out.length; i < ii; i++) {
-      const A = buf[(i << 2) + 3];
-      if (A === 0) {
-        max = out[i] = 0xff;
-        continue;
-      }
       const pix = (out[i] = buf[i << 2]);
-      if (pix > max) {
+      max = Math.max(max, pix);
-        max = pix;
+      min = Math.min(min, pix);
-      }
-      if (pix < min) {
-        min = pix;
-      }
     }
     const ratio = 255 / (max - min);
-    for (let i = 0; i < N; i++) {
+    for (let i = 0, ii = out.length; i < ii; i++) {
       out[i] = (out[i] - min) * ratio;
     }
 
@@ -468,6 +459,8 @@ class SignatureExtractor {
     }
     const offscreen = new OffscreenCanvas(newWidth, newHeight);
     const ctx = offscreen.getContext("2d", { willReadFrequently: true });
+    ctx.fillStyle = "white";
+    ctx.fillRect(0, 0, newWidth, newHeight);
     ctx.filter = "grayscale(1)";
     ctx.drawImage(
       bitmap,

test/integration/signature_editor_spec.mjs

@@ -718,4 +718,47 @@ describe("Signature Editor", () => {
       );
     });
   });
+
+  describe("Bug 1975719", () => {
+    let pages;
+
+    beforeEach(async () => {
+      pages = await loadAndWait("empty.pdf", ".annotationEditorLayer");
+    });
+
+    afterEach(async () => {
+      await closePages(pages);
+    });
+
+    it("must check that an error is displayed with a monochrome image", async () => {
+      await Promise.all(
+        pages.map(async ([_, page]) => {
+          await switchToSignature(page);
+
+          await page.click("#editorSignatureAddSignature");
+
+          await page.waitForSelector("#addSignatureDialog", {
+            visible: true,
+          });
+          await page.click("#addSignatureImageButton");
+          await page.waitForSelector("#addSignatureImagePlaceholder", {
+            visible: true,
+          });
+          const input = await page.$("#addSignatureFilePicker");
+          await input.uploadFile(
+            `${path.join(__dirname, "../images/red.png")}`
+          );
+          await page.waitForSelector("#addSignatureError", { visible: true });
+          await page.waitForSelector(
+            "#addSignatureErrorTitle[data-l10n-id='pdfjs-editor-add-signature-image-no-data-error-title']"
+          );
+          await page.waitForSelector(
+            "#addSignatureErrorDescription[data-l10n-id='pdfjs-editor-add-signature-image-no-data-error-description']"
+          );
+          await page.click("#addSignatureErrorCloseButton");
+          await page.waitForSelector("#addSignatureError", { visible: false });
+        })
+      );
+    });
+  });
 });

web/signature_manager.js

@@ -56,6 +56,10 @@ class SignatureManager {
 
   #errorBar;
 
+  #errorDescription;
+
+  #errorTitle;
+
   #extractedSignatureData = null;
 
   #imagePath = null;
@@ -123,6 +127,8 @@ class SignatureManager {
       addButton,
       errorCloseButton,
       errorBar,
+      errorTitle,
+      errorDescription,
       saveCheckbox,
       saveContainer,
     },
@@ -142,6 +148,8 @@ class SignatureManager {
     this.#drawPlaceholder = drawPlaceholder;
     this.#drawThickness = drawThickness;
     this.#errorBar = errorBar;
+    this.#errorTitle = errorTitle;
+    this.#errorDescription = errorDescription;
     this.#imageSVG = imageSVG;
     this.#imagePlaceholder = imagePlaceholder;
     this.#imagePicker = imagePicker;
@@ -161,6 +169,12 @@ class SignatureManager {
 
     SignatureManager.#l10nDescription ||= Object.freeze({
       signature: "pdfjs-editor-add-signature-description-default-when-drawing",
+      errorUploadTitle: "pdfjs-editor-add-signature-image-upload-error-title",
+      errorUploadDescription:
+        "pdfjs-editor-add-signature-image-upload-error-description",
+      errorNoDataTitle: "pdfjs-editor-add-signature-image-no-data-error-title",
+      errorNoDataDescription:
+        "pdfjs-editor-add-signature-image-no-data-error-description",
     });
 
     dialog.addEventListener("close", this.#close.bind(this));
@@ -506,6 +520,18 @@ class SignatureManager {
     );
   }
 
+  #showError(type) {
+    this.#errorTitle.setAttribute(
+      "data-l10n-id",
+      SignatureManager.#l10nDescription[`error${type}Title`]
+    );
+    this.#errorDescription.setAttribute(
+      "data-l10n-id",
+      SignatureManager.#l10nDescription[`error${type}Description`]
+    );
+    this.#errorBar.hidden = false;
+  }
+
   #initImageTab(reset) {
     if (reset) {
       this.#resetTab("image");
@@ -539,7 +565,7 @@ class SignatureManager {
       async () => {
         const file = this.#imagePicker.files?.[0];
         if (!file || !SupportedImageMimeTypes.includes(file.type)) {
-          this.#errorBar.hidden = false;
+          this.#showError("Upload");
           this.#dialog.classList.toggle("waiting", false);
           return;
         }
@@ -601,18 +627,19 @@ class SignatureManager {
       console.error("SignatureManager.#extractSignature.", e);
     }
     if (!data) {
-      this.#errorBar.hidden = false;
+      this.#showError("Upload");
       this.#dialog.classList.toggle("waiting", false);
       return;
     }
 
-    const { outline } = (this.#extractedSignatureData =
+    const lineData = (this.#extractedSignatureData =
       this.#currentEditor.getFromImage(data.bitmap));
-
+    if (!lineData) {
-    if (!outline) {
+      this.#showError("NoData");
       this.#dialog.classList.toggle("waiting", false);
       return;
     }
+    const { outline } = lineData;
 
     this.#imagePlaceholder.hidden = true;
     this.#disableButtons(true);

web/viewer.html

@@ -735,8 +735,8 @@ See https://github.com/adobe-type-tools/cmap-resources
               <div id="addSignatureError" hidden="true" class="messageBar">
                 <div>
                   <div>
-                    <span class="title" data-l10n-id="pdfjs-editor-add-signature-image-upload-error-title"></span>
+                    <span id="addSignatureErrorTitle" class="title" data-l10n-id="pdfjs-editor-add-signature-image-upload-error-title"></span>
-                    <span class="description" data-l10n-id="pdfjs-editor-add-signature-image-upload-error-description"></span>
+                    <span id="addSignatureErrorDescription" class="description" data-l10n-id="pdfjs-editor-add-signature-image-upload-error-description"></span>
                   </div>
                   <button id="addSignatureErrorCloseButton" class="closeButton" type="button" tabindex="0"><span data-l10n-id="pdfjs-editor-add-signature-error-close-button"></span></button>
                 </div>

web/viewer.js

@@ -227,6 +227,8 @@ function getViewerConfiguration() {
       saveContainer: document.getElementById("addSignatureSaveContainer"),
       saveCheckbox: document.getElementById("addSignatureSaveCheckbox"),
       errorBar: document.getElementById("addSignatureError"),
+      errorTitle: document.getElementById("addSignatureErrorTitle"),
+      errorDescription: document.getElementById("addSignatureErrorDescription"),
       errorCloseButton: document.getElementById("addSignatureErrorCloseButton"),
       cancelButton: document.getElementById("addSignatureCancelButton"),
       addButton: document.getElementById("addSignatureAddButton"),