Bug/498/signature slow firefox mobile (#3322)

# Description of Changes

Please provide a summary of the changes, including:

- What was changed
- Why the change was made
- Any challenges encountered

Closes #(498)

---

## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md#6-testing)
for more details.

---------

Co-authored-by: Reece Browne <reece@stirling.pdf>

src/main/resources/static/js/sign/signature-canvas.js

@@ -26,7 +26,6 @@ window.addEventListener("keydown", (event) => {
 
 function undoDraw() {
   const data = signaturePad.toData();
-
   if (data && data.length > 0) {
     const removed = data.pop();
     undoData.push(removed);
@@ -35,7 +34,6 @@ function undoDraw() {
 }
 
 function redoDraw() {
-
   if (undoData.length > 0) {
     const data = signaturePad.toData();
     data.push(undoData.pop());
@@ -52,24 +50,18 @@ function addDraggableFromPad() {
 }
 
 function getCroppedCanvasDataUrl(canvas) {
-  let originalCtx = canvas.getContext('2d');
+  let originalCtx = canvas.getContext('2d', { willReadFrequently: true });
   let originalWidth = canvas.width;
   let originalHeight = canvas.height;
   let imageData = originalCtx.getImageData(0, 0, originalWidth, originalHeight);
 
-  let minX = originalWidth + 1,
+  let minX = originalWidth + 1, maxX = -1, minY = originalHeight + 1, maxY = -1;
-    maxX = -1,
-    minY = originalHeight + 1,
-    maxY = -1,
-    x = 0,
-    y = 0,
-    currentPixelColorValueIndex;
 
-  for (y = 0; y < originalHeight; y++) {
+  for (let y = 0; y < originalHeight; y++) {
-    for (x = 0; x < originalWidth; x++) {
+    for (let x = 0; x < originalWidth; x++) {
-      currentPixelColorValueIndex = (y * originalWidth + x) * 4;
+      let idx = (y * originalWidth + x) * 4;
-      let currentPixelAlphaValue = imageData.data[currentPixelColorValueIndex + 3];
+      let alpha = imageData.data[idx + 3];
-      if (currentPixelAlphaValue > 0) {
+      if (alpha > 0) {
         if (minX > x) minX = x;
         if (maxX < x) maxX = x;
         if (minY > y) minY = y;
@@ -81,14 +73,14 @@ function getCroppedCanvasDataUrl(canvas) {
   let croppedWidth = maxX - minX;
   let croppedHeight = maxY - minY;
   if (croppedWidth < 0 || croppedHeight < 0) return null;
-  let cuttedImageData = originalCtx.getImageData(minX, minY, croppedWidth, croppedHeight);
+  let cutImageData = originalCtx.getImageData(minX, minY, croppedWidth, croppedHeight);
 
-  let croppedCanvas = document.createElement('canvas'),
+  let croppedCanvas = document.createElement('canvas');
-    croppedCtx = croppedCanvas.getContext('2d');
+  let croppedCtx = croppedCanvas.getContext('2d');
 
   croppedCanvas.width = croppedWidth;
   croppedCanvas.height = croppedHeight;
-  croppedCtx.putImageData(cuttedImageData, 0, 0);
+  croppedCtx.putImageData(cutImageData, 0, 0);
 
   return croppedCanvas.toDataURL();
 }
@@ -114,10 +106,20 @@ function resizeCanvas() {
   signaturePad.clear();
 }
 
-new IntersectionObserver((entries, observer) => {
+const debounce = (fn, delay = 100) => {
+  let timer;
+  return (...args) => {
+    clearTimeout(timer);
+    timer = setTimeout(() => fn(...args), delay);
+  };
+};
+
+const debouncedResize = debounce(resizeCanvas, 200);
+
+new IntersectionObserver((entries) => {
   if (entries.some((entry) => entry.intersectionRatio > 0)) {
-    resizeCanvas();
+    debouncedResize();
   }
 }).observe(signaturePadCanvas);
 
-new ResizeObserver(resizeCanvas).observe(signaturePadCanvas);
+new ResizeObserver(debouncedResize).observe(signaturePadCanvas);

src/main/resources/templates/sign.html

@@ -43,13 +43,13 @@
             </div>
             <script type="module" th:src="@{'/pdfjs-legacy/pdf.mjs'}"></script>
             <div class="tab-group show-on-file-selected">
-              <div class="tab-container" th:title="#{sign.upload}" th:data-title="#{sign.upload}">
+              <div class="tab-container"th:data-title="#{sign.upload}">
                 <div
                   th:replace="~{fragments/common :: fileSelector(name='image-upload', disableMultipleFiles=false, multipleInputsForSingleRequest=true, accept='image/*', inputText=#{imgPrompt})}">
                 </div>
               </div>
 
-              <div class="tab-container drawing-pad-container" th:title="#{sign.draw}" th:data-title="#{sign.draw}">
+              <div class="tab-container drawing-pad-container"  th:data-title="#{sign.draw}">
                 <canvas id="drawing-pad-canvas"></canvas>
                 <br>
                 <button id="clear-signature" class="btn btn-outline-danger mt-2" onclick="signaturePad.clear()"
@@ -62,7 +62,7 @@
                   onclick="redoDraw()"></button>
               </div>
 
-              <div class="tab-container" th:title="#{sign.saved}" th:data-title="#{sign.saved}">
+              <div class="tab-container"  th:data-title="#{sign.saved}">
                 <div class="saved-signatures-section" th:if="${not #lists.isEmpty(signatures)}">
 
                   <!-- Preview Modal -->
@@ -134,7 +134,7 @@
                 </div>
               </div>
 
-              <div class="tab-container" th:title="#{sign.text}" th:data-title="#{sign.text}">
+              <div class="tab-container" th:data-title="#{sign.text}">
                 <label class="form-check-label" for="sigText" th:text="#{text}"></label>
                 <textarea class="form-control" id="sigText" name="sigText" rows="3"></textarea>
                 <label th:text="#{font}"></label>