线段上的水平和垂直翻转

Question

I have a set (c++ vector) of points (x,y) that defines a line. How do I implement a function that returns the samle line, flipped horizontal and vertical relative to its own size?

Answer 1

I assume that you mean you're not flipping with respect to some fixed origin; you're flipping with respect to the centroid of the line.

Here's some pseudocode:

Get the min and max y and x in the vector
Height = yMax - yMin
Width = xMax - xMin
yCentroid = yMin + (Height / 2)
xCentroid = xMin + (Width / 2)

for each point...
  xNew = xMax - (xOld - xMin)
  yNew = yMax - (yOld - yMin)

For example, if we had a simple 3-point line from (-5, 3) to (7, 4) to (11, -1), this would give us a flipped line from (11, 0) to (-1, -1) to (-5, 4). This is shown in the blue example below.

It also works for several points, as shown in the green example below.