Qt 绘制线段

1. float x1 = lastPoint.x();         //lastPoint 起点
3. float y1 = lastPoint.y();
5. float x2 = endPoint.x();           //endPoint 终点
7. float y2 = endPoint.y();
9. float l = 10.0;                   //箭头的那长度
11. float a = 0.5;                       //箭头与线段角度
13. float x3 = x2 - l * cos(atan2((y2 - y1) , (x2 - x1)) - a);
15. float y3 = y2 - l * sin(atan2((y2 - y1) , (x2 - x1)) - a);
17. float x4 = x2 - l * sin(atan2((x2 - x1) , (y2 - y1)) - a);
19. float y4 = y2 - l * cos(atan2((x2 - x1) , (y2 - y1)) - a);
21. painter.drawLine(x1,y1,x3,y3);
23. painter.drawLine(x1,y1,x4,y4);
25. painter.drawLine(lastPoint,endPoint);