canvas 后期笔记

canvas 公式

   

 ## 角度旋转
    dx = mouse.x - object.x;
    dy = mouse.y - object.y;
    object.rotation = Math.atan2(dy,dx)*180/Math.PI
 
    ## 平滑运动
       value = center + Math.sin(angle)*range;
       angle += speed;
 
    ## 正圆运动
       x_position = centerX + Math.sin(angle)*radius;
       y_position = centerY + Math.cos(angle)*radius;
       angle += speed;
 
    ## 椭圆运动
       x_position = centerX + Math.cos(angle)*radiusX;
       y_position = centerY + Math.sin(angle)*radiusY;
       angle += speed;
 
    ##两点间距离
    dx = x2 - x1;
    dy = y2 - y1;
    dist = Math.sqrt(dx*dx + dy*dy);