feat: add fallback placeholder image

src/editor/core/draw/particle/ImageParticle.ts

@@ -1,5 +1,6 @@
 import { IEditorOption } from '../../../interface/Editor'
 import { IElement } from '../../../interface/Element'
+import { convertStringToBase64 } from '../../../utils'
 import { Draw } from '../Draw'
 
 export class ImageParticle {
@@ -18,6 +19,24 @@ export class ImageParticle {
     this.draw.getImageObserver().add(promise)
   }
 
+  protected getFallbackImage(width: number, height: number): HTMLImageElement {
+    const tileSize = 8
+    const x = (width - Math.ceil(width / tileSize) * tileSize) / 2
+    const y = (height - Math.ceil(height / tileSize) * tileSize) / 2
+    const svg = `<svg xmlns="http://www.w3.org/2000/svg" width="${width}" height="${height}" viewBox="0 0 ${width} ${height}">
+                  <rect width="${width}" height="${height}" fill="url(#mosaic)" />
+                  <defs>
+                    <pattern id="mosaic" x="${x}" y="${y}" width="${tileSize * 2}" height="${tileSize * 2}" patternUnits="userSpaceOnUse">
+                      <rect width="${tileSize}" height="${tileSize}" fill="#cccccc" />
+                      <rect width="${tileSize}" height="${tileSize}" fill="#cccccc" transform="translate(${tileSize}, ${tileSize})" />
+                    </pattern>
+                  </defs>
+                </svg>`
+    const fallbackImage = new Image()
+    fallbackImage.src = `data:image/svg+xml;base64,${convertStringToBase64(svg)}`
+    return fallbackImage
+  }
+
   public render(ctx: CanvasRenderingContext2D, element: IElement, x: number, y: number) {
     const { scale } = this.options
     const width = element.width! * scale
@@ -36,6 +55,11 @@ export class ImageParticle {
           resolve(element)
         }
         img.onerror = (error) => {
+          const fallbackImage = this.getFallbackImage(width, height)
+          fallbackImage.onload = () => {
+            ctx.drawImage(fallbackImage, x, y, width, height)
+            this.imageCache.set(element.id!, fallbackImage)
+          }
           reject(error)
         }
       })

src/editor/utils/index.ts

@@ -148,4 +148,12 @@ export function cloneProperty<T>(properties: (keyof T)[], sourceElement: T, targ
       delete targetElement[property]
     }
   }
+}
+
+export function convertStringToBase64(input: string) {
+  const encoder = new TextEncoder()
+  const data = encoder.encode(input)
+  const charArray = Array.from(data, byte => String.fromCharCode(byte))
+  const base64 = window.btoa(charArray.join(''))
+  return base64
 }