图形种类
目前我们软件可以绘制出来的形状有如下这几种，作为开发者我们一直想支持用户可以拖拽的类似word里面图形库，但目前还没有找到比较合适的库。
下图中所有的图形都是我们自己写代码在canvas上绘制方法出来的，可以改变实心/空心，改变颜色，大小宽高，线条弯曲度，透明度等。
父类shape类
实现的代码如下：所有的图形均继承自shape类，而shape类继承自CommonElement，shape中的所有图形添加到画布上都是一个元素。
这个类里面有很多功能函数：
prepareStyle() { //绘制准备context绘制属性
setPro() { }//绘制前准备参数
public thiner() {//变细
public thicker() {//加粗
changeColor(color: string, callBack: Function) {//改变绘制颜色
changeAlpha(alpha: number, callBack: Function) {//改变透明度
changeFill(isFill: boolean) {//切换实心空心
drawPath() { }//绘制图形路径，所有图形都会重写该方法
draw() {//绘制调用入口
1 export class Shape extends CommonElement {
2 shapeParameter: ShapeParameter;
3 tempFill: boolean;
4 tempStroke: boolean;
5 constructor(id: string, config: Config, context: CanvasRenderingContext2D, shapeParameter: ShapeParameter, typeName) {
6 super(id, config, context, typeName);
7 this.shapeParameter = shapeParameter;
8 }
9 prepareStyle() { //绘制准备context绘制属性
10 if (this.shapeParameter.computeLineWidth && this.shapeParameter.isStroke) {
11 this.shapeParameter.lineWidth = Math.max(2, Math.min(this.config.width * editor.canvas.canvasImp.scale, this.config.height * editor.canvas.canvasImp.scale) / this.shapeParameter.lineWidthScale);
12
13 }
14 var ctx = this.context;
15 ctx.fillStyle = Common.Util.makeRGBA(this.shapeParameter.fillStyle, this.shapeParameter.alpha);
16 ctx.strokeStyle = Common.Util.makeRGBA(this.shapeParameter.strokeStyle, this.shapeParameter.alpha);
17 ctx.lineWidth = this.shapeParameter.lineWidth / editor.canvas.canvasImp.scale;
18
19 }
20 public setPro() { }//绘制前准备参数
21 public drawPath() { }//绘制图形路径，所有图形都会重写该方法
22 public draw() {//绘制调用入口
23 //保存context状态
24 this.context.save();
25 this.rotate();//将画布旋转到位
26 this.setPro();
27 this.prepareStyle();
28 this.drawPath();
29 //恢复context状态
30 this.context.restore();
31 }
32
所有图形类都有的一个属性ShapeParameter 具体内容如下，每个属性值都有各自的作用
1 export class ShapeParameter {//图形属性参数
2 lineWidth: number;
3 isFill: boolean;
4 isStroke: boolean
5 fillStyle: string;
6 strokeStyle: string
7 lineWidthScale: number;
8 isAutiClockwise: boolean;
9 computeLineWidth: boolean;
10 alpha: number;
11 lineDash: any;
12 constructor() {
13 this.lineWidth = 1;
14 this.isStroke = true;
15 this.isFill = false;
16 this.fillStyle = editor.currentShapeColor || editor.canvas.canvasImp.theme.shapeColor;
17 this.strokeStyle = editor.currentShapeColor || editor.canvas.canvasImp.theme.shapeColor;
18 this.lineWidthScale = lineWidthScale;
19 this.isAutiClockwise = false;
20 this.computeLineWidth = true;
21 this.alpha = editor.currentShapAlpha || 1;
22 this.lineDash = [10, 15];
23 }
24 }
特殊图形绘制计算方法
下面介绍几种绘制各种图形用到的特殊计算方法
如下图中的一个线条，我们可以拖拽中间控制点形成一个弧，这个弧形是某个圆的一部分。
我们定义左侧的第一个点为startPoint，中间的点为controlPoint，右侧的点为endPoint。
我们在绘制出这个图形时，需要知道如何求这三个点确定的圆的圆心坐标怎么计算，还有通过两点计算（x1,y1）为圆心,圆上某点（x2,y2）的角度的计算方法
1 GetCenter(): Point {//获取三个点，确定的一个圆的中心点坐标
2 var p1 = this.startPoint;
3 var p2 = this.controlPoint;
4 var p3 = this.endPoint;
5 var C1 = new Point((p1.x + p2.x) / 2.0, (p1.y + p2.y) / 2.0);
6 var C2 = new Point((p2.x + p3.x) / 2.0, (p2.y + p3.y) / 2.0);
7 var I = new Point(0, 0);;
8 var k1: number, k2: number;
9 if ((p2.y - p1.y) == 0.0) {
10 if ((p3.y - p2.y) == 0.0) {
11 return null;
12 } else {
13 k2 = -1 * (p3.x - p2.x) / (p3.y - p2.y);
14 I.x = C1.x; I.y = k2 * (I.x - C2.x) + C2.y;
15 }
16 } else {
17 k1 = -1 * (p2.x - p1.x) / (p2.y - p1.y);
18 if ((p3.y - p2.y) == 0.0) {
19 I.x = C2.x;
20 I.y = k1 * (I.x - C1.x) + C1.y;
21 } else {
22 k2 = -1 * (p3.x - p2.x) / (p3.y - p2.y);
23 if (k1 == k2) {
24 return null;
25 } else {
26 I.x = (C2.y - C1.y + k1 * C1.x - k2 * C2.x) / (k1 - k2); I.y = k1 * (I.x - C1.x) + C1.y;
27 }
28 }
29 }
30 return I;
31 }
1 //通过两点计算x1,y1为圆心,圆上某点（x2,y2）的角度（按照arc的角度计算）
2 static computeAng(x1, y1, x2, y2) {
3 var ang = (x1 - x2) / (y1 - y2);
4 ang = Math.atan(ang);
5 if (x1 == x2 && y2 > y1) {
6 return 0.5 * Math.PI;
7 }
8 if (x1 == x2 && y2 < y1) {
9 return 1.5 * Math.PI;
10 }
11 if (y1 == y2 && x2 > x1) {
12 return 0;
13 }
14 if (y1 == y2 && x2 < x1) {
15 return Math.PI;
16 }
17 if (x2 > x1 && y2 > y1) {
18 return Math.PI / 2 - ang;
19 }
20 else if (x2 < x1 && y2 > y1) {
21 return Math.PI / 2 - ang;
22 }
23 else if (x2 < x1 && y2 < y1) {
24 return 3 * Math.PI / 2 - ang;
25 }
26 else if (x2 > x1 && y2 < y1) {
27 return 3 * Math.PI / 2 - ang;
28 }
29 }
另外再介绍一下我们的这个箭头是如何实现的
1 drawIsosceles(context: CanvasRenderingContext2D) {//画等腰箭头
2 var triangleSide = this.triangleSide;
3 //First the center of the triangle base (where we start to draw the triangle)
4 var centerBaseArrowX = this.basePoint.x ;
5 var centerBaseArrowY = this.basePoint.y;
6
7 //Let's calculate the first point, easy!
8 var ax = centerBaseArrowX + (triangleSide / 2) * Math.cos(this.centerAngle);
9 var ay = centerBaseArrowY + (triangleSide / 2) * Math.sin(this.centerAngle);
10
11 //Now time to get mad: the farest triangle point from the arrow body
12 var bx = centerBaseArrowX + (1/ 2/Math.sqrt(3) ) * triangleSide * (Math.sin(-this.centerAngle));
13 var by = centerBaseArrowY + ( 1/ 2/Math.sqrt(3)) * triangleSide * (Math.cos(-this.centerAngle));
14
15 //Easy , like the a point
16 var cx = centerBaseArrowX - (triangleSide / 2) * Math.cos(this.centerAngle);
17 var cy = centerBaseArrowY - (triangleSide / 2) * Math.sin(this.centerAngle);
18
19 context.beginPath();
20 //We move to the center of the base
21 context.moveTo(centerBaseArrowX, centerBaseArrowY);
22 context.lineTo(ax, ay);
23 context.lineTo(bx, by);
24 context.lineTo(cx, cy);
25 context.lineTo(centerBaseArrowX, centerBaseArrowY);
26 context.fill();
27 }
在canvas上绘制多边形的方法
drawPath(context: CanvasRenderingContext2D) {
for (var ixVertex = 0; ixVertex <= this.nPoints; ++ixVertex) {
var angle = ixVertex * 2 * Math.PI / this.nPoints - this.startAngle;
var point = new Point(this.centerPoint.x + this.radius * Math.cos(angle), this.centerPoint.y + this.radius * Math.sin(angle));
context.lineTo(point.x, point.y);
}
}
在canvas上绘制五角星等多角形的方法
1 drawPath(context:CanvasRenderingContext2D) {
2 for (var ixVertex = 0; ixVertex <= 2 * this.nPoints; ++ixVertex) {
3 var angle = ixVertex * Math.PI / this.nPoints - Math.PI / 2;
4 var radius = ixVertex % 2 == 0 ? this.outerRadius : this.innerRadius;
5 context.lineTo(this.centerPoint.x + radius * Math.cos(angle), this.centerPoint.y + radius * Math.sin(angle));
6 }
7 }