[Editor] Use the alt text to descibe the canvas used to display the image

src/display/editor/editor.js

@@ -927,6 +927,9 @@ class AnnotationEditor {
     if (!tooltip.parentNode) {
       button.append(tooltip);
     }
+
+    const element = this.getImageForAltText();
+    element?.setAttribute("aria-describedby", tooltip.id);
   }
 
   #toggleAltTextButton(enabled = false) {
@@ -960,6 +963,9 @@ class AnnotationEditor {
     };
   }
 
+  /**
+   * Set the alt text data.
+   */
   set altTextData({ altText, decorative }) {
     if (this.#altText === altText && this.#altTextDecorative === decorative) {
       return;
@@ -1369,6 +1375,13 @@ class AnnotationEditor {
    */
   enterInEditMode() {}
 
+  /**
+   * @returns {HTMLElement | null} the element requiring an alt text.
+   */
+  getImageForAltText() {
+    return null;
+  }
+
   /**
    * Get the div which really contains the displayed content.
    * @returns {HTMLDivElement | undefined}

src/display/editor/stamp.js

@@ -32,6 +32,8 @@ class StampEditor extends AnnotationEditor {
 
   #bitmapFile = null;
 
+  #bitmapFileName = "";
+
   #canvas = null;
 
   #observer = null;
@@ -104,6 +106,9 @@ class StampEditor extends AnnotationEditor {
       this.#bitmapId = data.id;
       this.#isSvg = data.isSvg;
     }
+    if (data.file) {
+      this.#bitmapFileName = data.file.name;
+    }
     this.#createCanvas();
   }
 
@@ -332,6 +337,9 @@ class StampEditor extends AnnotationEditor {
       },
     });
     this.addAltTextButton();
+    if (this.#bitmapFileName) {
+      canvas.setAttribute("aria-label", this.#bitmapFileName);
+    }
   }
 
   /**
@@ -438,6 +446,11 @@ class StampEditor extends AnnotationEditor {
     );
   }
 
+  /** @inheritdoc */
+  getImageForAltText() {
+    return this.#canvas;
+  }
+
   #serializeBitmap(toUrl) {
     if (toUrl) {
       if (this.#isSvg) {