update: 端口移动以1px的距离跳跃，而非连续。

fix：端口间连线对不齐的问题。

src/kit/extensions/PortShiftingTool.ts

@@ -148,6 +148,10 @@ export class PortShiftingTool extends go.Tool {
     const br = main.getDocumentPoint(go.Spot.BottomRight);
     const x = Math.max(0, Math.min((last.x - tl.x) / (br.x - tl.x), 1));
     const y = Math.max(0, Math.min((last.y - tl.y) / (br.y - tl.y), 1));
-    this.port.alignment = new go.Spot(x, y);
+    const parent_x = br.x - tl.x
+    const parent_y = br.y - tl.y
+    const dx = Math.round(parent_x * x)
+    const dy = Math.round(parent_y * y)
+    this.port.alignment = new go.Spot(dx/parent_x, dy/parent_y);
   }
 }