如何使用触摸旋转图像

Question

谁能告诉我如何根据用户给出的触摸旋转视图....

我的意思是我想做出类似旧电话的外观（按下并旋转拨号...）...

我非常了解如何旋转，但根据这种情况无法旋转.....

Answer 1

你需要一个只有表盘图像的视图。

This view has a center C(x,y)
First, the view will be touched at coordinate T0(x,y)

if the x and y is within the circle do the tracking:
    Then the finger will move to coordinate Tn(x,y) 
    Find the angle made up by Tn(x,y) C(x,y) T0(x,y)  //(See below for a reference)
    and do the rotation using that angle as you already know ;)
else
   do nothing since the touch is not in the dial 

参考：How to calculate an angle from three points

Answer 2

计算开始触摸与表盘中心 (atan2f(y - yc, x - xc)) 之间的角度，并将其用作确定每个后续触摸事件所需的旋转的基础角度。