getTile support cssFilter

src/cavnas.js

@@ -74,3 +74,19 @@ export function toBlobURL(imagebitmap) {
     ctx.drawImage(imagebitmap, 0, 0);
     return canvas.convertToBlob();
 }
+
+export function imageFilter(canvas, imagebitmap, filter) {
+    if (!filter) {
+        return imagebitmap;
+    }
+    canvas.width = imagebitmap.width;
+    canvas.height = imagebitmap.height;
+    const ctx = getCanvasContext(canvas);
+    clearCanvas(ctx);
+    ctx.save();
+    ctx.filter = filter;
+    ctx.drawImage(imagebitmap, 0, 0);
+    ctx.restore();
+    const bitImage = canvas.transferToImageBitmap();
+    return bitImage;
+}

src/tileget.js

@@ -1,11 +1,23 @@
+import { getCanvas, imageFilter } from './cavnas';
+
 export function getTile(url, options = {}) {
     return new Promise((resolve, reject) => {
         if (!url) {
             reject(new Error('url is null'));
             return;
         }
         fetch(url).then(res => res.blob()).then(blob => createImageBitmap(blob)).then(imagebit => {
-            resolve(imagebit);
+            const filter = options.filter;
+            if (filter) {
+                const canvas = getCanvas();
+                if (!canvas) {
+                    reject(new Error('not find canvas.The current environment does not support OffscreenCanvas'));
+                } else {
+                    resolve(imageFilter(canvas, imagebit, filter));
+                }
+            } else {
+                resolve(imagebit);
+            }
         }).catch(error => {
             reject(error);
         });