01.float x1 = lastPoint.x(); //lastPoint 起点
02.
03.float y1 = lastPoint.y();
04.
05.float x2 = endPoint.x(); //endPoint 终点
06.
07.float y2 = endPoint.y();
08.
09.float l = 10.0; //箭头的那长度
10.
11.float a = 0.5; //箭头与线段角度
12.
13.float x3 = x2 - l * cos(atan2((y2 - y1) , (x2 - x1)) - a);
14.
15.float y3 = y2 - l * sin(atan2((y2 - y1) , (x2 - x1)) - a);
16.
17.float x4 = x2 - l * sin(atan2((x2 - x1) , (y2 - y1)) - a);
18.
19.float y4 = y2 - l * cos(atan2((x2 - x1) , (y2 - y1)) - a);
20.
21.painter.drawLine(x1,y1,x3,y3);
22.
23.painter.drawLine(x1,y1,x4,y4);
24.
25.painter.drawLine(lastPoint,endPoint);