线性变换

transform/rotate.py

@@ -0,0 +1,42 @@
+import math
+from trans import linear_trans
+
+def rotate_point(p1:list[float],p2:list[float],dgr:float) -> list[float]:
+    '''
+    Rotate p1 with p2 for dgr.
+    dgr measured in radians.
+    '''
+    arr = [
+        [math.cos(dgr),-math.sin(dgr)],
+        [math.sin(dgr), math.cos(dgr)]
+    ]
+    vec = [p1[0]-p2[0],p1[1]-p2[1]]
+    rvec = linear_trans(arr,vec)
+    return  [p2[0]+rvec[0], p2[1]+rvec[1]]
+
+def rotate_line(line,p,dgr):
+    '''
+    Rotate y=kx+b with p for dgr.
+    dgr measured in radians.
+    @param line:
+        tuple[k, b] => y = kx + b
+    
+    '''
+    k,b = line
+    arr = [
+        [math.cos(dgr),-math.sin(dgr)],
+        [math.sin(dgr), math.cos(dgr)]
+    ]
+    vec  = [1, k]
+    rvec = linear_trans(arr,vec)
+    rk = rvec[1]/rvec[0] # (a,b) => (1,b/a)
+    
+    p1 = [0,b]
+    rp1 = rotate_point(p1,p,dgr)
+    
+    return [rk,rp1[1]-rk*rp1[0]]
+    
+    
+
+if __name__ == "__main__":
+    print(rotate_line((3,4),(2,1),math.pi/4))