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如何将图形的拖动和调整大小限制在 Canvas 舞台内

本示例演示如何将图形的拖动和调整大小限制在 Canvas 舞台边界内。通过实现自定义边界函数，可以防止图形被移动到可见区域外，也可以防止图形在调整大小后超出该区域。

此实现结合了拖动限制示例和调整大小限制示例中的技术，以限制用户交互。

操作说明： 尝试旋转、拖动图形或调整图形大小。观察这些图形如何被限制在 Canvas 边界内。

import Konva from 'konva';

// Helper functions for calculating bounding boxes
function getCorner(pivotX, pivotY, diffX, diffY, angle) {
  const distance = Math.sqrt(diffX * diffX + diffY * diffY);

  // Find angle from pivot to corner
  angle += Math.atan2(diffY, diffX);

  // Get new x and y coordinates
  const x = pivotX + distance * Math.cos(angle);
  const y = pivotY + distance * Math.sin(angle);

  return { x, y };
}

// Calculate client rect accounting for rotation
function getClientRect(rotatedBox) {
  const { x, y, width, height } = rotatedBox;
  const rad = rotatedBox.rotation;

  const p1 = getCorner(x, y, 0, 0, rad);
  const p2 = getCorner(x, y, width, 0, rad);
  const p3 = getCorner(x, y, width, height, rad);
  const p4 = getCorner(x, y, 0, height, rad);

  const minX = Math.min(p1.x, p2.x, p3.x, p4.x);
  const minY = Math.min(p1.y, p2.y, p3.y, p4.y);
  const maxX = Math.max(p1.x, p2.x, p3.x, p4.x);
  const maxY = Math.max(p1.y, p2.y, p3.y, p4.y);

  return {
    x: minX,
    y: minY,
    width: maxX - minX,
    height: maxY - minY,
  };
}

// Calculate total bounding box of multiple shapes
function getTotalBox(boxes) {
  let minX = Infinity;
  let minY = Infinity;
  let maxX = -Infinity;
  let maxY = -Infinity;

  boxes.forEach((box) => {
    minX = Math.min(minX, box.x);
    minY = Math.min(minY, box.y);
    maxX = Math.max(maxX, box.x + box.width);
    maxY = Math.max(maxY, box.y + box.height);
  });
  
  return {
    x: minX,
    y: minY,
    width: maxX - minX,
    height: maxY - minY,
  };
}

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

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

// Create first shape (red rectangle)
const shape1 = new Konva.Rect({
  x: stage.width() / 2 - 60,
  y: stage.height() / 2 - 60,
  width: 50,
  height: 50,
  fill: 'red',
  draggable: true,
});
layer.add(shape1);

// Create second shape (green rectangle)
const shape2 = shape1.clone({
  x: stage.width() / 2 + 10,
  y: stage.height() / 2 + 10,
  fill: 'green',
});
layer.add(shape2);

// Add transformer that includes both shapes
const tr = new Konva.Transformer({
  nodes: [shape1, shape2],
  // Set boundary function for resize operations
  boundBoxFunc: (oldBox, newBox) => {
    // Calculate the actual bounding box of the transformed shape
    const box = getClientRect(newBox);
    
    // Check if the new box is outside the stage boundaries
    const isOut =
      box.x < 0 ||
      box.y < 0 ||
      box.x + box.width > stage.width() ||
      box.y + box.height > stage.height();

    // If outside boundaries, keep the old box
    if (isOut) {
      return oldBox;
    }
    
    // If within boundaries, allow the transformation
    return newBox;
  },
});
layer.add(tr);

// Handle drag events to keep shapes within the stage
tr.on('dragmove', () => {
  // Get client rects for all selected nodes
  const boxes = tr.nodes().map((node) => node.getClientRect());
  
  // Get the total bounding box of all shapes
  const box = getTotalBox(boxes);
  
  // Keep shapes within stage boundaries
  tr.nodes().forEach((shape) => {
    const absPos = shape.getAbsolutePosition();
    
    // Calculate shape position relative to group bounding box
    const offsetX = box.x - absPos.x;
    const offsetY = box.y - absPos.y;

    // Adjust position if outside boundaries
    const newAbsPos = { ...absPos };
    
    if (box.x < 0) {
      newAbsPos.x = -offsetX;
    }
    if (box.y < 0) {
      newAbsPos.y = -offsetY;
    }
    if (box.x + box.width > stage.width()) {
      newAbsPos.x = stage.width() - box.width - offsetX;
    }
    if (box.y + box.height > stage.height()) {
      newAbsPos.y = stage.height() - box.height - offsetY;
    }
    
    shape.setAbsolutePosition(newAbsPos);
  });
});
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