背景说明

基于UI同学的设计，在市面上找不到刚刚好的数据标注工具，遂决定自行开发。目前需求是实现图片的矩形、圆形标注，并获取标注的坐标信息，使用canvas可以比较方便的实现该功能。

主要功能

选中图形，进行拖动

使用事件监听，mousedown确认鼠标按下坐标是否在图形内，mousemove提供坐标来更新图形坐标。

选中小圆点，进行缩放

使用事件监听，mousedown确认鼠标按下坐标是否在小圆点内，mousemove提供坐标来更新图形宽高（或半径）。

基础方法

// 获取canvas元素
const canvas = document.getElemnetById("canvas") as HtmlCanvasElement;
// 获取canvas上下文
const ctx = canvas.getContent("2d");
// 画矩形
ctx.beginPath();

ctx.rect(x, y, w, h); // 参数：左上角坐标x,y 宽高wh

ctx.fillStyle = color1; // 填充色
ctx.strokeStyle = color2; // 线条色
ctx.lineWidth = width1; // 线条宽

ctx.fill(); // 填充
ctx.stroke(); // 画线

ctx.closePath();
// 画圆形
ctx.beginPath();

ctx.arc(x, y, r, 0, Math.PI * 2); // 参数：中心点坐标x,y 半径2 从0角度绘制到Math.PI*2角度

ctx.fillStyle = color1;
ctx.strokeStyle = color2;
ctx.lineWidth = width1;

ctx.fill();
ctx.stroke();

ctx.closePath();

主要方法

新增图形

定义图形类，以矩形为例

export class Rectangle {

    x!: number;
    y!: number;
    w!: number;
    h!: number;
    fillColor!: string;
    strokeColor!: string;
    strokeWidth!: number;

    selectedDotIndex = -1;
    uuid!: string;
    isInsideDotFlag = false;

    dotR = 7;
    dotLineWidth = 2;
    dotFillColor = '#3D7FFF';
    dotStrokeColor = '#FFFFFF';
    dotConnectLineStorkeColor = '#3D7FFF';
    dotConnectLineWidth = 1;
    // 最小11x11
    minSize = 11;

    constructor(x: number, y: number, w: number, h: number, fillColor: string, storkeColor: string, storkeWidth: number) {
        this.x = x;
        this.y = y;
        this.w = w;
        this.h = h;
        this.fillColor = fillColor;
        this.strokeColor = storkeColor;
        this.strokeWidth = storkeWidth;

        this.uuid = this.generateUUID();
    }

    // 小圆点坐标
    get dots() {
        return [
            [this.x, this.y],
            [this.x + this.w / 2, this.y],
            [this.x + this.w, this.y],
            [this.x + this.w, this.y + this.h / 2],
            [this.x + this.w, this.y + this.h],
            [this.x + this.w / 2, this.y + this.h],
            [this.x, this.y + this.h],
            [this.x, this.y + this.h / 2]
        ];
    }

    // 是否在小圆点内
    isInsideDot(x: number, y: number) {
        for (let index = 0; index < this.dots.length; index++) {
            const [dx, dy] = this.dots[index];
            if (this.distanceBetweenTwoPoints(x, y, dx, dy) < this.dotR) {
                this.selectedDotIndex = index;
                return true;
            }
        }
        this.selectedDotIndex = -1;
        return false;
    }

    // 是否在图形内
    isInsideShape(x: number, y: number) {
        this.isInsideDotFlag = this.isInsideDot(x, y);
        if (this.isInsideDotFlag) { // 在小圆点内也算在图形内
            return true;
        }
        return x >= this.x && x <= (this.x + this.w) && y >= this.y && y <= (this.y + this.h);
    }

    // 更新小圆点
    updateDot(mouseX: number, mouseY: number) {
        const handleIndex = this.selectedDotIndex;
        switch (handleIndex) {
            case 0: // 左上角
                this.w = this.x + this.w - mouseX;
                this.h = this.y + this.h - mouseY;
                this.x = mouseX;
                this.y = mouseY;
                break;
            case 1: // 上边中点
                this.h = this.y + this.h - mouseY;
                this.y = mouseY;
                break;
            case 2: // 右上角
                this.w = mouseX - this.x;
                this.h = this.y + this.h - mouseY;
                this.y = mouseY;
                break;
            case 3: // 右边中点
                this.w = mouseX - this.x;
                break;
            case 4: // 右下角
                this.w = mouseX - this.x;
                this.h = mouseY - this.y;
                break;
            case 5: // 下边中点
                this.h = mouseY - this.y;
                break;
            case 6: // 左下角
                this.w = this.x + this.w - mouseX;
                this.h = mouseY - this.y;
                this.x = mouseX;
                break;
            case 7: // 左边中点
                this.w = this.x + this.w - mouseX;
                this.x = mouseX;
                break;
            default:
                break;
        }

        this.w = Math.max(this.w, this.minSize);
        this.h = Math.max(this.h, this.minSize);
    }

    // 更新坐标
    updateXy(mouseX: number, mouseY: number) {
        this.x = mouseX - this.w / 2;
        this.y = mouseY - this.h / 2;
    }

    // 画小圆点
    drawDots(ctx: CanvasRenderingContext2D) {
        for (let index = 0; index < this.dots.length; index++) {
            const [x1, y1] = this.dots[index];
            const [x2, y2] = this.dots[(index + 1) % this.dots.length];
            // 点
            ctx.beginPath();
            ctx.arc(x1, y1, this.dotR, 0, Math.PI * 2);
            ctx.fillStyle = this.dotFillColor;
            ctx.strokeStyle = this.dotStrokeColor;
            ctx.lineWidth = this.dotLineWidth;
            ctx.fill();
            ctx.stroke();
            ctx.closePath();
            // 线
            ctx.beginPath();
            ctx.moveTo(x1, y1);
            ctx.lineTo(x2, y2);
            ctx.strokeStyle = this.dotConnectLineStorkeColor;
            ctx.lineWidth = this.dotConnectLineWidth;
            ctx.fill();
            ctx.stroke();
            ctx.closePath();
        }
    }

    // 画图
    draw(ctx: CanvasRenderingContext2D) {
        ctx.beginPath();

        ctx.rect(this.x, this.y, this.w, this.h);

        ctx.fillStyle = this.fillColor;
        ctx.strokeStyle = this.strokeColor;
        ctx.lineWidth = this.strokeWidth;

        ctx.fill();
        ctx.stroke();
        ctx.closePath();
    }

    // 获取uuid
    generateUUID() {
        var random = Math.random().toString(36).substring(2);
        var timestamp = new Date().getTime().toString(36);
        return random + timestamp;
    }

    // 计算2点之间的距离
    distanceBetweenTwoPoints(x1: number, y1: number, x2: number, y2: number) {
        const xDiff = x1 - x2;
        const yDiff = y1 - y2;
        return Math.sqrt(Math.pow(xDiff, 2) + Math.pow(yDiff, 2));
    }

    // 获取左上、右下坐标
    getPoints() {
        return [this.x, this.y, this.x + this.w, this.y + this.h];
    }
}

添加图形：把图形对象加入列表，方便管理

const rect = new Rectangle(this.startX, this.startY, 120, 120, this.hexToRgba(color, 0.3), color, 3);
this.dataList.unshift({
  name: '矩形',
  type: 'Rectangle',
  color,
  shape: rect
});

绘制图形：根据列表进行绘制

reDraw() {
	// 清空画布
	this.ctxFront.clearRect(0, 0, this.canvasFrontEle.width, this.canvasFrontEle.height);
	for (let index = 0; index < this.dataList.length; index++) {
	  const shape = this.dataList[index].shape;
	  shape.draw(this.ctxFront);
	  // 选中的图形绘制小圆点
	  if (this.selectedShape && shape.uuid === this.selectedShape.uuid) {
	    shape.drawDots(this.ctxFront);
	  }
	}
}

事件监听

// 监听canvas事件
listenCanvas() {
 // 事件监听
 // 鼠标按下
 this.canvasFrontEle.onmousedown = (e) => {
   const rect = this.canvasFrontEle.getBoundingClientRect();
   const clickX = e.clientX - rect.left;
   const clickY = e.clientY - rect.top;

   for (let index = 0; index < this.dataList.length; index++) {
     const shape = this.dataList[index].shape;
     if (shape.isInsideShape(clickX, clickY)) {
       this.selectedShape = shape;
       break;
     } else if (index === this.dataList.length - 1) {
       this.selectedShape = null;
     }
   }

   if (this.selectedShape) { // 选中图形
     if (this.selectedShape.isInsideDotFlag) { // 在顶点
       window.onmousemove = (e) => {
         const moveX = e.clientX - rect.left;
         const moveY = e.clientY - rect.top;
         this.selectedShape!.updateDot(moveX, moveY);
         this.reDraw();
       };
     } else { // 移动
       window.onmousemove = (e) => {
         const moveX = e.clientX - rect.left;
         const moveY = e.clientY - rect.top;
         this.selectedShape!.updateXy(moveX, moveY);
         this.reDraw();
       };
     }
   }
   this.reDraw();

   window.onmouseup = (e) => {
     window.onmousemove = null;
     window.onmouseup = null;
   }
 };
}