feat: [SAM] able to download the result as png (#1035)

* feat: able to download the result as png

* feat: update function and wording

candle-wasm-examples/segment-anything/lib-example.html

@@ -73,9 +73,12 @@
         statusOutput.innerText = event.data.message;
       }
 
+      let copyMaskURL = null;
+      let copyImageURL = null;
       const clearBtn = document.querySelector("#clear-btn");
       const maskBtn = document.querySelector("#mask-btn");
       const undoBtn = document.querySelector("#undo-btn");
+      const downloadBtn = document.querySelector("#download-btn");
       const canvas = document.querySelector("#canvas");
       const mask = document.querySelector("#mask");
       const ctxCanvas = canvas.getContext("2d");
@@ -93,6 +96,7 @@
         if (target.files.length > 0) {
           const href = URL.createObjectURL(target.files[0]);
           clearImageCanvas();
+          copyImageURL = href;
           drawImageCanvas(href);
           setImageEmbeddings(href);
           togglePointMode(false);
@@ -119,11 +123,13 @@
         if (files.length > 0) {
           const href = URL.createObjectURL(files[0]);
           clearImageCanvas();
+          copyImageURL = href;
           drawImageCanvas(href);
           setImageEmbeddings(href);
           togglePointMode(false);
         } else if (url) {
           clearImageCanvas();
+          copyImageURL = url;
           drawImageCanvas(url);
           setImageEmbeddings(url);
           togglePointMode(false);
@@ -145,6 +151,7 @@
         if (target.nodeName === "IMG") {
           const href = target.src;
           clearImageCanvas();
+          copyImageURL = href;
           drawImageCanvas(href);
           setImageEmbeddings(href);
         }
@@ -163,6 +170,46 @@
       undoBtn.addEventListener("click", () => {
         undoPoint();
       });
+      // add event to download btn
+      downloadBtn.addEventListener("click", async () => {
+        // Function to load image blobs as Image elements asynchronously
+        const loadImageAsync = (imageURL) => {
+          return new Promise((resolve) => {
+            const img = new Image();
+            img.onload = () => {
+              resolve(img);
+            };
+            img.crossOrigin = "anonymous";
+            img.src = imageURL;
+          });
+        };
+        const originalImage = await loadImageAsync(copyImageURL);
+        const maskImage = await loadImageAsync(copyMaskURL);
+
+        // create main a board to draw
+        const canvas = document.createElement("canvas");
+        const ctx = canvas.getContext("2d");
+        canvas.width = originalImage.width;
+        canvas.height = originalImage.height;
+
+        // Perform the mask operation
+        ctx.drawImage(maskImage, 0, 0);
+        ctx.globalCompositeOperation = "source-in";
+        ctx.drawImage(originalImage, 0, 0);
+
+        // to blob
+        const blobPromise = new Promise((resolve) => {
+          canvas.toBlob(resolve);
+        });
+        const blob = await blobPromise;
+        const resultURL = URL.createObjectURL(blob);
+
+        // download
+        const link = document.createElement("a");
+        link.href = resultURL;
+        link.download = "cutout.png";
+        link.click();
+      });
       //add click event to canvas
       canvas.addEventListener("click", async (event) => {
         if (!hasImage || isEmbedding || isSegmenting) {
@@ -185,14 +232,17 @@
           pointArr = [...pointArr, [x, y, !backgroundMode]];
         }
         undoBtn.disabled = false;
+        downloadBtn.disabled = false;
         if (pointArr.length == 0) {
           ctxMask.clearRect(0, 0, canvas.width, canvas.height);
           undoBtn.disabled = true;
+          downloadBtn.disabled = true;
           return;
         }
         isSegmenting = true;
         const { maskURL } = await getSegmentationMask(pointArr);
         isSegmenting = false;
+        copyMaskURL = maskURL;
         drawMask(maskURL, pointArr);
       });
 
@@ -212,6 +262,7 @@
         isSegmenting = true;
         const { maskURL } = await getSegmentationMask(pointArr);
         isSegmenting = false;
+        copyMaskURL = maskURL;
         drawMask(maskURL, pointArr);
       }
       function togglePointMode(mode) {
@@ -490,6 +541,15 @@
             <img
               src="https://huggingface.co/datasets/huggingface/badges/raw/main/share-to-community-sm.svg" />
           </button>
+
+          <button
+            id="download-btn"
+            title="Copy result (.png)"
+            disabled
+            class="p-1 px-2 text-xs font-medium bg-white rounded-2xl outline outline-gray-200 hover:outline-orange-200 disabled:opacity-50"
+          >
+            Download Cut-Out
+          </button>
         </div>
       </div>
       <div>