Merge branch 'dev' of github.com:dcloudio/uni-app into dev

src/core/view/components/canvas/index.vue

@@ -133,8 +133,10 @@ export default {
         method(data)
       }
     },
-    _resize () {
+    _resize (size) {
       var canvas = this.$refs.canvas
+      var hasChanged = !size || (canvas.width !== size.width * pixelRatio || canvas.height !== size.height * pixelRatio)
+      if (!hasChanged) return
       if (canvas.width > 0 && canvas.height > 0) {
         var context = canvas.getContext('2d')
         var imageData = context.getImageData(0, 0, canvas.width, canvas.height)