如何通过边缘拖动自动滚动舞台？

如何通过边缘拖动自动滚动舞台？

在 Konva.js 应用中实现自动滚动功能，可以改善用户体验。此功能特别适合需要拖动项目或浏览大型 Canvas 的交互式 UI。当用户把项目拖到视口底部或右侧边缘时，滚动区域会自动移动，从而使交互更加流畅直观。

Vanilla

import Konva from 'konva';

const stage = new Konva.Stage({
  container: 'container',
  width: window.innerWidth,
  height: window.innerHeight,
});

const layer = new Konva.Layer();
stage.add(layer);

const NUMBER = 100;

function generateNode() {
  return new Konva.Circle({
    x: stage.width() * (Math.random() * 2 - 1),
    y: stage.height() * (Math.random() * 2 - 1),
    radius: 40,
    fill: 'red',
    stroke: 'black',
    draggable: true,
  });
}

for (let i = 0; i < NUMBER; i++) {
  layer.add(generateNode());
}

let scrollInterval = null;

stage.on('dragstart', (e) => {
  const duration = 1000 / 60;
  scrollInterval = setInterval(() => {
    const pos = stage.getPointerPosition();
    const offset = 100;
    
    const isNearLeft = pos.x < offset;
    if (isNearLeft) {
      stage.x(stage.x() + 2);
      e.target.x(e.target.x() - 2);
    }
    
    const isNearRight = pos.x > stage.width() - offset;
    if (isNearRight) {
      stage.x(stage.x() - 2);
      e.target.x(e.target.x() + 2);
    }
    
    const isNearTop = pos.y < offset;
    if (isNearTop) {
      stage.y(stage.y() + 2);
      e.target.y(e.target.y() - 2);
    }
    
    const isNearBottom = pos.y > stage.height() - offset;
    if (isNearBottom) {
      stage.y(stage.y() - 2);
      e.target.y(e.target.y() + 2);
    }
  }, duration);
});

stage.on('dragend', () => {
  clearInterval(scrollInterval);
});

Open Sandbox

React

import React from 'react';
import { Stage, Layer, Circle } from 'react-konva';

const NUMBER = 100;

const generateNodes = (width, height) => {
  return Array.from({ length: NUMBER }, () => ({
    x: width * (Math.random() * 2 - 1),
    y: height * (Math.random() * 2 - 1),
  }));
};

const App = () => {
  const [stagePos, setStagePos] = React.useState({ x: 0, y: 0 });
  const [nodes, setNodes] = React.useState([]);
  const scrollInterval = React.useRef(null);
  const stageRef = React.useRef(null);
  const draggedNodeRef = React.useRef(null);

  React.useEffect(() => {
    setNodes(generateNodes(window.innerWidth, window.innerHeight));
  }, []);

  const handleDragStart = React.useCallback((e) => {
    draggedNodeRef.current = e.target;
    const duration = 1000 / 60;
    scrollInterval.current = setInterval(() => {
      const stage = stageRef.current;
      if (!stage) return;

      const pos = stage.getPointerPosition();
      if (!pos) return;

      const offset = 100;
      let newX = stagePos.x;
      let newY = stagePos.y;
      let moved = false;

      if (pos.x < offset) {
        newX += 2;
        draggedNodeRef.current.x(draggedNodeRef.current.x() - 2);
        moved = true;
      } else if (pos.x > stage.width() - offset) {
        newX -= 2;
        draggedNodeRef.current.x(draggedNodeRef.current.x() + 2);
        moved = true;
      }

      if (pos.y < offset) {
        newY += 2;
        draggedNodeRef.current.y(draggedNodeRef.current.y() - 2);
        moved = true;
      } else if (pos.y > stage.height() - offset) {
        newY -= 2;
        draggedNodeRef.current.y(draggedNodeRef.current.y() + 2);
        moved = true;
      }

      if (moved) {
        setStagePos({ x: stage.x() + newX, y: stage.y() + newY });
      }
    }, duration);
  }, [stagePos]);

  const handleDragEnd = React.useCallback(() => {
    draggedNodeRef.current = null;
    if (scrollInterval.current) {
      clearInterval(scrollInterval.current);
      scrollInterval.current = null;
    }
  }, []);

  React.useEffect(() => {
    return () => {
      if (scrollInterval.current) {
        clearInterval(scrollInterval.current);
      }
    };
  }, []);

  return (
    <Stage
      width={window.innerWidth}
      height={window.innerHeight}
      x={stagePos.x}
      y={stagePos.y}
      ref={stageRef}
    >
      <Layer>
        {nodes.map((node, i) => (
          <Circle
            key={i}
            x={node.x}
            y={node.y}
            radius={40}
            fill="red"
            stroke="black"
            draggable
            onDragStart={handleDragStart}
            onDragEnd={handleDragEnd}
          />
        ))}
      </Layer>
    </Stage>
  );
};

export default App;

Open Sandbox

Vue

<template>
  <v-stage
    :config="stageConfig"
    ref="stageRef"
  >
    <v-layer>
      <v-circle
        v-for="(node, i) in nodes"
        :key="i"
        :config="{
          x: node.x,
          y: node.y,
          radius: 40,
          fill: 'red',
          stroke: 'black',
          draggable: true,
          onDragStart: handleDragStart,
          onDragEnd: handleDragEnd,
        }"
      />
    </v-layer>
  </v-stage>
</template>

<script setup>
import { ref, computed, onMounted, onUnmounted } from 'vue';

const NUMBER = 100;
const stageRef = ref(null);
const stagePos = ref({ x: 0, y: 0 });
const nodes = ref([]);
let scrollInterval = null;
let draggedNode = null;

const stageConfig = computed(() => ({
  width: window.innerWidth,
  height: window.innerHeight,
  x: stagePos.value.x,
  y: stagePos.value.y,
}));

function generateNodes() {
  return Array.from({ length: NUMBER }, () => ({
    x: window.innerWidth * (Math.random() * 2 - 1),
    y: window.innerHeight * (Math.random() * 2 - 1),
  }));
}

const handleDragStart = (e) => {
  draggedNode = e.target;
  const duration = 1000 / 60;
  scrollInterval = setInterval(() => {
    const stage = stageRef.value.getNode();
    const pos = stage.getPointerPosition();
    if (!pos) return;

    const offset = 100;
    let newX = stagePos.value.x;
    let newY = stagePos.value.y;
    let moved = false;

    if (pos.x < offset) {
      newX += 2;
      draggedNode.x(draggedNode.x() - 2);
      moved = true;
    } else if (pos.x > stage.width() - offset) {
      newX -= 2;
      draggedNode.x(draggedNode.x() + 2);
      moved = true;
    }

    if (pos.y < offset) {
      newY += 2;
      draggedNode.y(draggedNode.y() - 2);
      moved = true;
    } else if (pos.y > stage.height() - offset) {
      newY -= 2;
      draggedNode.y(draggedNode.y() + 2);
      moved = true;
    }

    if (moved) {
      stagePos.value = { x: newX, y: newY };
    }
  }, duration);
};

const handleDragEnd = () => {
  draggedNode = null;
  if (scrollInterval) {
    clearInterval(scrollInterval);
    scrollInterval = null;
  }
};

onMounted(() => {
  nodes.value = generateNodes();
});

onUnmounted(() => {
  if (scrollInterval) {
    clearInterval(scrollInterval);
  }
});
</script>

Open Sandbox

操作说明： 开始拖动任意图形。将图形拖到舞台边缘附近时，舞台会自动向该方向滚动，从而实现流畅的无限滚动体验。