Qt 绘制线段

float x1 = lastPoint.x();         //lastPoint 起点

float y1 = lastPoint.y();

float x2 = endPoint.x();           //endPoint 终点

float y2 = endPoint.y();

float l = 10.0;                   //箭头的那长度

float a = 0.5;                       //箭头与线段角度

float x3 = x2 - l * cos( atan2((y2 - y1) , (x2 - x1)) - a);

float y3 = y2 - l * sin( atan2((y2 - y1) , (x2 - x1)) - a);

float x4 = x2 - l * sin( atan2((x2 - x1) , (y2 - y1)) - a);

float y4 = y2 - l * cos( atan2((x2 - x1) , (y2 - y1)) - a);

painter.drawLine(x1,y1,x3,y3);

painter.drawLine(x1,y1,x4,y4);

painter.drawLine(lastPoint,endPoint);