Chore: improve the /dither page

src/routes/dither/+page.svelte

@@ -14,22 +14,37 @@
   let offscreenCanvas: OffscreenCanvas;
   let ctx = $derived(canvas.getContext('2d'))
   let offscreenCtx: OffscreenCanvasRenderingContext2D;
-  let imgObjectUrl = $state('')
+  let selectedImage: HTMLImageElement | null = $state(null)
   let errorMessage = $state('')
+  let selectedAlgorithm = $state('atkinson')
+
+  let maxImageWidth = $state(0)
+  let imageHeightRatio = $state(0)
+  let imageWidthPc = $state(100)
 
   onMount(() => {
    offscreenCanvas = new OffscreenCanvas(1000, 1000)
    offscreenCtx = offscreenCanvas.getContext('2d')
   })
 
-  const doesCtxExist = () => {
-    if (!ctx) {
-      errorMessage = "Problem finding context for on-screen canvas"
-      return false
+  $effect(() => {
+    if (!selectedImage) {
+      console.log(`Selected Image is null, terminating effect...`)
+      return;
     }
 
-    return true;
-  }
+    maxImageWidth = selectedImage.width 
+    imageHeightRatio = selectedImage.height / selectedImage.width
+
+    ctx.clearRect(0, 0, canvas.width, canvas.height)
+
+    canvas.width = maxImageWidth * (imageWidthPc/100)
+    canvas.height = imageHeightRatio * canvas.width
+    ctx.drawImage(selectedImage, 0, 0, canvas.width, canvas.height)
+
+    const imageData = ctx.getImageData(0, 0, canvas.width, canvas.height)
+    ctx.putImageData(DITHERING_ALGORITHMS[selectedAlgorithm](imageData), 0, 0)
+  })
 
   const handleImageChange = async (event: any) => {
     const file = event.target.files[0];
@@ -38,18 +53,8 @@
       return
     }
 
-    imgObjectUrl = URL.createObjectURL(file);
-    const image = await createImage(imgObjectUrl);
-
-    // Change the sizes of canvases
-    canvas.width = image.width
-    canvas.height = image.height
-
-    offscreenCanvas.height = image.height
-    offscreenCanvas.width = image.width
-
-    // Now draw the images 
-    drawImage(image)
+    const imgObjectUrl = URL.createObjectURL(file);
+    selectedImage = await createImage(imgObjectUrl);
   }
 
   async function createImage(objectUrl: string):  Promise<HTMLImageElement> {
@@ -63,30 +68,7 @@
     });
   }
 
-  const clearCanvases = () => {
-    ctx.clearRect(0, 0, canvas.width, canvas.height);
-    offscreenCtx.clearRect(0, 0, offscreenCanvas.width, offscreenCanvas.height);
-  }
-
-  const drawImage = (theImage: HTMLImageElement) => {
-    if (!doesCtxExist()) return
-    clearCanvases()
-    ctx.drawImage(theImage, 0, 0, canvas.width, canvas.height);  
-    offscreenCtx.drawImage(theImage, offscreenCanvas.width, offscreenCanvas.height)
-  }
-
-  function applyDitheringAlgorithm(algorithm: (imageData: ImageData) => ImageData) {
-    return async () => {
-      const freshImage = await createImage(imgObjectUrl);
-      drawImage(freshImage)
-      const imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);
-      const ditheredImageData = algorithm(imageData);
-      ctx.putImageData(ditheredImageData, 0, 0);
-    }
-  }
-
   function saveImage() {
-    if (!canvas) return;
     const link = document.createElement('a');
     link.download = 'dithered-image.png';
     link.href = canvas.toDataURL();
@@ -95,7 +77,7 @@
 
 </script>
 
-<ErrorMessage message={errorMessage} />
+<ErrorMessage errorMessage={errorMessage} />
 
 <h2 class="page-dither__subtitle">1: Select a file</h2>
 
@@ -108,9 +90,9 @@
 <h2 class="page-dither__subtitle">2: Select a dithering algorithm</h2>
 
 <ul class="algorithms">
-  {#each Object.entries(DITHERING_ALGORITHMS) as [key, value]}
+  {#each Object.keys(DITHERING_ALGORITHMS) as key}
     <li class="algorithms__item">
-      <button class="algorithms__button" onclick={applyDitheringAlgorithm(value)}>{key}</button>
+      <button class="algorithms__button" onclick={() => selectedAlgorithm = key}>{key}</button>
     </li>
   {/each}
 </ul>
@@ -120,9 +102,20 @@
   <canvas id="photo-canvas" height="250" bind:this={canvas} onload={() => ctx = canvas.getContext('2d')}></canvas>
 </div>
 
+<h2 class="page-dither__subtitle">
+  3: Remix 
+</h2>
+
+<form>
+  <label for="resolution">
+    Image Ratio
+    <input type="range" min="1" max="100" step="5" bind:value={imageWidthPc} width="100%"/>
+  </label>
+  <p>{maxImageWidth * imageWidthPc / 100}</p>
+</form>
 
 <h2 class="page-dither__subtitle">
-  3: Save the file
+  4: Save the file
 </h2>
 <button onclick={saveImage}>Save Image</button>
 

src/routes/dither/ErrorMessage.svelte

@@ -1,5 +1,8 @@
 <script lang="ts">
-  const { errorMessage } = $props()
+  interface Props {
+    errorMessage: string;
+  }
+  const { errorMessage }: Props = $props()
 </script>
 
 {#if errorMessage}