Fix：修复节点数量很多的情况下，导出图片节点显示不全的问题

simple-mind-map/src/plugins/Export.js

@@ -144,6 +144,7 @@ class Export {
         try {
           const canvas = document.createElement('canvas')
           const dpr = Math.max(window.devicePixelRatio, minExportImgCanvasScale)
+          // 图片原始大小
           let imgWidth = img.width
           let imgHeight = img.height
           // 如果是裁减操作的话，那么需要手动添加内边距，及调整图片大小为实际的裁减区域的大小，不要忘了内边距哦
@@ -184,6 +185,8 @@ class Export {
           }
           // 检查是否超出canvas支持的像素上限
           // canvas大小需要乘以dpr
+          let scaleX = 1
+          let scaleY = 1
           let canvasWidth = (fitBgImgWidth || imgWidth) * dpr
           let canvasHeight = (fitBgImgHeight || imgHeight) * dpr
           if (canvasWidth > maxCanvasSize || canvasHeight > maxCanvasSize) {
@@ -203,6 +206,8 @@ class Export {
               newWidth,
               newHeight
             )
+            scaleX = res[0] / canvasWidth
+            scaleY = res[1] / canvasHeight
             canvasWidth = res[0]
             canvasHeight = res[1]
           }
@@ -210,6 +215,7 @@ class Export {
           canvas.height = canvasHeight
           const styleWidth = canvasWidth / dpr
           const styleHeight = canvasHeight / dpr
+          // canvas元素实际上的大小
           canvas.style.width = styleWidth + 'px'
           canvas.style.height = styleHeight + 'px'
           const ctx = canvas.getContext('2d')
@@ -221,9 +227,9 @@ class Export {
           // 图片绘制到canvas里
           // 如果有裁减数据，那么需要进行裁减
           const fitBgLeft =
-            fitBgImgWidth > 0 ? (fitBgImgWidth - imgWidth) / 2 : 0
+            (fitBgImgWidth > 0 ? (fitBgImgWidth - imgWidth) / 2 : 0) * scaleX
           const fitBgTop =
-            fitBgImgHeight > 0 ? (fitBgImgHeight - imgHeight) / 2 : 0
+            (fitBgImgHeight > 0 ? (fitBgImgHeight - imgHeight) / 2 : 0) * scaleY
           if (clipData) {
             ctx.drawImage(
               img,
@@ -231,13 +237,19 @@ class Export {
               clipData.top,
               clipData.width,
               clipData.height,
-              paddingX + fitBgLeft,
-              paddingY + fitBgTop,
-              clipData.width,
-              clipData.height
+              paddingX * scaleX + fitBgLeft,
+              paddingY * scaleY + fitBgTop,
+              clipData.width * scaleX,
+              clipData.height * scaleY
             )
           } else {
-            ctx.drawImage(img, fitBgLeft, fitBgTop, imgWidth, imgHeight)
+            ctx.drawImage(
+              img,
+              fitBgLeft,
+              fitBgTop,
+              imgWidth * scaleX,
+              imgHeight * scaleY
+            )
           }
           resolve(canvas.toDataURL(format))
         } catch (error) {