fix: background zoom mismatch between cached and real-time calculated result

src/components/background.svelte

@@ -1,20 +1,29 @@
 <script lang="ts">
     import { processImage } from '$lib/graphics';
-    import localforage from 'localforage';
-    // Initialize IndexedDB
-    localforage.config({
-        driver: localforage.INDEXEDDB,
-        name: 'audioDB'
-    });
-
+    import blobToImageData from '$lib/graphics/blob2imageData';
+    import imageDataToBlob from '$lib/graphics/imageData2blob';
+    import localforage from '$lib/storage';
     export let coverId: string;
     let canvas: HTMLCanvasElement;
-    localforage.getItem(`${coverId}-cover`, function (err, file) {
-        console.log(file);
-        console.log(err);
+
+    let flag = false;
+    localforage.getItem(`${coverId}-cover-cache`, function (err, file) {
         if (file) {
-            const path = URL.createObjectURL(file as File);
-            processImage(16, 4, 96, path, canvas);
+            const ctx = canvas.getContext('2d');
+            blobToImageData(file as Blob).then((imageData) => {
+                console.log(imageData);
+                ctx?.putImageData(imageData,0,0);
+            })
+            
+        } else {
+            localforage.getItem(`${coverId}-cover`, function (err, file) {
+                if (file) {
+                    const path = URL.createObjectURL(file as File);
+                    processImage(16, 3, 96, path, canvas, (resultImageData: ImageData) => {
+                        localforage.setItem(`${coverId}-cover-cache`, imageDataToBlob(resultImageData));
+                    });
+                }
+            });
         }
     });
 </script>
@@ -37,8 +46,8 @@
     }
     canvas {
         position: relative;
-        width: 110%;
-        height: 110%;
         object-fit: cover;
+        width: 100%;
+        height: 100%;
     }
 </style>

src/lib/graphics/blob2imageData.ts

@@ -0,0 +1,17 @@
+export default function blobToImageData(blob: Blob): Promise<ImageData> {
+    return new Promise((resolve, reject) => {
+        const reader = new FileReader();
+        reader.onload = (event) => {
+            const arrayBuffer = event.target?.result as ArrayBuffer;
+            const dataView = new DataView(arrayBuffer);
+            const width = dataView.getUint32(0, true); // Read width from little-endian bytes
+            const height = dataView.getUint32(4, true); // Read height from little-endian bytes
+            const byteArray = new Uint8ClampedArray(arrayBuffer, 8); // Skip the header
+            resolve(new ImageData(byteArray, width, height));
+        };
+        reader.onerror = () => {
+            reject(new Error("Failed to read Blob as ArrayBuffer"));
+        };
+        reader.readAsArrayBuffer(blob);
+    });
+}

src/lib/graphics/imageData2blob.ts

@@ -0,0 +1,11 @@
+export default function imageDataToBlob(imageData: ImageData): Blob {
+    const width = imageData.width;
+    const height = imageData.height;
+    const data = new Uint8ClampedArray(imageData.data);
+    const header = new Uint8Array(8); // 4 bytes for width, 4 bytes for height
+    const dataView = new DataView(header.buffer);
+    dataView.setUint32(0, width, true); // Store width in little-endian
+    dataView.setUint32(4, height, true); // Store height in little-endian
+    const blob = new Blob([header, data], { type: 'image/png' });
+    return blob;
+}

src/lib/graphics/index.ts

@@ -1,46 +1,34 @@
-import { gaussianBlurHorizontal, gaussianBlurVertical, applyFilter } from "./utils";
+import { gaussianBlurHorizontal, gaussianBlurVertical, applyFilter } from './utils';
 
-export async function processImage(blockSize: number, resolutionFactor:number, radius:number, path: string, canvas: HTMLCanvasElement) {
-    const ctx = canvas.getContext("2d")!;
+export function processImage(
+    blockSize: number,
+    resolutionFactor: number,
+    radius: number,
+    path: string,
+    canvas: HTMLCanvasElement,
+    callback: (resultImageData: ImageData) => void
+) {
+    const ctx = canvas.getContext('2d')!;
 
     const image = new Image();
     image.src = path; // Replace with your image path
 
     image.onload = function () {
         // Resize image to 1/9 of the original resolution
+        const width = image.width;
+        const height = image.height;
         const resizedWidth = image.width / resolutionFactor;
         const resizedHeight = image.height / resolutionFactor;
 
-        const num_blocks_x = Math.floor(resizedWidth / blockSize);
-        const num_blocks_y = Math.floor(resizedHeight / blockSize);
-
         canvas.width = resizedWidth;
         canvas.height = resizedHeight;
-
-        for (let i = 0; i < num_blocks_y; i++) {
-            for (let j = 0; j < num_blocks_x; j++) {
-                const block = document.createElement("canvas");
-                block.width = blockSize;
-                block.height = blockSize;
-
-                const blockCtx = block.getContext("2d")!;
-                blockCtx.drawImage(
-                    image,
-                    j * blockSize * resolutionFactor,
-                    i * blockSize * resolutionFactor,
-                    blockSize * resolutionFactor,
-                    blockSize * resolutionFactor,
-                    0,
-                    0,
-                    blockSize,
-                    blockSize
-                );
-
-                applyFilter(block);
-
-                ctx.drawImage(block, j * blockSize, i * blockSize);
-            }
-        }
+        const block = document.createElement('canvas');
+        const blockCtx = block.getContext('2d')!;
+        block.width = image.width;
+        block.height = image.height;
+        blockCtx.drawImage(image, 0, 0, width, height, 0, 0, resizedWidth, resizedHeight);
+        applyFilter(block);
+        ctx.drawImage(block, 0, 0);
 
         // Horizontal Gaussian blur
         const imageDataHorizontal = ctx.getImageData(0, 0, canvas.width, canvas.height);
@@ -50,6 +38,7 @@ export async function processImage(blockSize: number, resolutionFactor:number, r
         const imageDataVertical = blurredImageDataHorizontal;
         const blurredImageData = gaussianBlurVertical(imageDataVertical, radius);
 
-        ctx.putImageData(blurredImageData, 0, 0);
+        ctx.putImageData(blurredImageData, 0, 0, 0, 0, width, height);
+        callback(blurredImageData);
     };
-}
+}

src/lib/storage.ts

@@ -0,0 +1,8 @@
+import localforage from "localforage";
+
+localforage.config({
+    driver: localforage.INDEXEDDB,
+    name: 'audioDB'
+});
+
+export default localforage;

src/routes/+page.svelte

@@ -15,7 +15,6 @@
         // Handle audio input change
         audioInput.addEventListener('change', function (e: any) {
             const file: File = e.target.files[0];
-            console.log(file.size);
             if (file) {
                 localforage.setItem(audioId + '-file', file);
             }