algorithm - 如何将线段绕其中心旋转 90 度？

Question

因为我数学很烂，this paper on the topic一个字都听不懂, 和 this answer I found对我来说解释得不够清楚，有人可以用伪代码向我展示用于旋转线段的算法，比如在 (50,40) - (50,120) 处围绕其中心点(90 度)绘制的图表？非常感谢。

Answer 1

90 度是一个简单的特例。假设您有一条从 (x1,y1) 到 (x2,y2) 的行:

//find the center
cx = (x1+x2)/2;
cy = (y1+y2)/2;

//move the line to center on the origin
x1-=cx; y1-=cy;
x2-=cx; y2-=cy;

//rotate both points
xtemp = x1; ytemp = y1;
x1=-ytemp; y1=xtemp; 

xtemp = x2; ytemp = y2;
x2=-ytemp; y2=xtemp; 

//move the center point back to where it was
x1+=cx; y1+=cy;
x2+=cx; y2+=cy;