1、需求
实现Canvas绘制多边形。
2、效果
3、代码
官方Demo是HTML版本的，我改写了React版本。
// Copyright 2021 zhaoarden
import React, { useState,useCallback } from 'react';
import { fabric } from "fabric";
import { Button } from 'antd';
class Polygon extends React.Component {
constructor(props) {
super(props);
this.state={
canvas:{}
}
}
componentDidMount(){
console.log('componentDidMount');
const canvas = new fabric.Canvas('c');
console.log('canvas',canvas);
this.setState({canvas:canvas})
// console.log('state-canvas',this.state.canvas);
var points = [{
x: 3, y: 4
}, {
x: 16, y: 3
}, {
x: 30, y: 5
}, {
x: 25, y: 55
}, {
x: 19, y: 44
}, {
x: 15, y: 30
}, {
x: 15, y: 55
}, {
x: 9, y: 55
}, {
x: 6, y: 53
}, {
x: -2, y: 55
}, {
x: -4, y: 40
}, {
x: 0, y: 20
}]
var polygon = new fabric.Polygon(points, {
left: 100,
top: 50,
fill: '#D81B60',
strokeWidth: 4,
stroke: 'green',
scaleX: 4,
scaleY: 4,
objectCaching: false,
transparentCorners: false,
cornerColor: 'blue',
});
canvas.viewportTransform = [0.7, 0, 0, 0.7, -50, 50];
canvas.add(polygon);
}
render() {
const controls={
display: 'inline-block'
};
const {canvas}=this.state
// define a function that can locate the controls.
// this function will be used both for drawing and for interaction.
function polygonPositionHandler(dim, finalMatrix, fabricObject) {
var x = (fabricObject.points[this.pointIndex].x - fabricObject.pathOffset.x),
y = (fabricObject.points[this.pointIndex].y - fabricObject.pathOffset.y);
return fabric.util.transformPoint(
{ x: x, y: y },
fabric.util.multiplyTransformMatrices(
fabricObject.canvas.viewportTransform,
fabricObject.calcTransformMatrix()
)
);
}
// define a function that will define what the control does
// this function will be called on every mouse move after a control has been
// clicked and is being dragged.
// The function receive as argument the mouse event, the current trasnform object
// and the current position in canvas coordinate
// transform.target is a reference to the current object being transformed,
function actionHandler(eventData, transform, x, y) {
var polygon = transform.target,
currentControl = polygon.controls[polygon.__corner],
mouseLocalPosition = polygon.toLocalPoint(new fabric.Point(x, y), 'center', 'center'),
polygonBaseSize = polygon._getNonTransformedDimensions(),
size = polygon._getTransformedDimensions(0, 0),
finalPointPosition = {
x: mouseLocalPosition.x * polygonBaseSize.x / size.x + polygon.pathOffset.x,
y: mouseLocalPosition.y * polygonBaseSize.y / size.y + polygon.pathOffset.y
};
polygon.points[currentControl.pointIndex] = finalPointPosition;
return true;
}
// define a function that can keep the polygon in the same position when we change its
// width/height/top/left.
function anchorWrapper(anchorIndex, fn) {
return function (eventData, transform, x, y) {
var fabricObject = transform.target,
absolutePoint = fabric.util.transformPoint({
x: (fabricObject.points[anchorIndex].x - fabricObject.pathOffset.x),
y: (fabricObject.points[anchorIndex].y - fabricObject.pathOffset.y),
}, fabricObject.calcTransformMatrix()),
actionPerformed = fn(eventData, transform, x, y),
newDim = fabricObject._setPositionDimensions({}),
polygonBaseSize = fabricObject._getNonTransformedDimensions(),
newX = (fabricObject.points[anchorIndex].x - fabricObject.pathOffset.x) / polygonBaseSize.x,
newY = (fabricObject.points[anchorIndex].y - fabricObject.pathOffset.y) / polygonBaseSize.y;
fabricObject.setPositionByOrigin(absolutePoint, newX + 0.5, newY + 0.5);
return actionPerformed;
}
}
function Edit() {
console.log('canvas',canvas);
console.log('Edit');
// clone what are you copying since you
// may want copy and paste on different moment.
// and you do not want the changes happened
// later to reflect on the copy.
var poly = canvas.getObjects()[0];
canvas.setActiveObject(poly);
poly.edit = !poly.edit;
if (poly.edit) {
var lastControl = poly.points.length - 1;
poly.cornerStyle = 'circle';
poly.cornerColor = 'rgba(0,0,255,0.5)';
poly.controls = poly.points.reduce(function (acc, point, index) {
acc['p' + index] = new fabric.Control({
positionHandler: polygonPositionHandler,
actionHandler: anchorWrapper(index > 0 ? index - 1 : lastControl, actionHandler),
actionName: 'modifyPolygon',
pointIndex: index
});
return acc;
}, {});
} else {
poly.cornerColor = 'blue';
poly.cornerStyle = 'rect';
poly.controls = fabric.Object.prototype.controls;
}
poly.hasBorders = !poly.edit;
canvas.requestRenderAll();
}
return
Learn, {this.props.name}
;
}
}
export default Polygon;