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- // Copyright 2021 The Gitea Authors. All rights reserved.
- // Use of this source code is governed by a MIT-style
- // license that can be found in the LICENSE file.
-
- // Copied and modified from https://github.com/issue9/identicon/ (MIT License)
-
- package identicon
-
- var (
- // cos(0),cos(90),cos(180),cos(270)
- cos = []int{1, 0, -1, 0}
-
- // sin(0),sin(90),sin(180),sin(270)
- sin = []int{0, 1, 0, -1}
- )
-
- // rotate the points by center point (x,y)
- // angle: [0,1,2,3] means [0,90,180,270] degree
- func rotate(points []int, x, y int, angle int) {
- // the angle is only used internally, and it has been guaranteed to be 0/1/2/3, so we do not check it again
- for i := 0; i < len(points); i += 2 {
- px, py := points[i]-x, points[i+1]-y
- points[i] = px*cos[angle] - py*sin[angle] + x
- points[i+1] = px*sin[angle] + py*cos[angle] + y
- }
- }
-
- // check whether the point is inside the polygon (defined by the points)
- // the first and the last point must be the same
- func pointInPolygon(x, y int, polygonPoints []int) bool {
- if len(polygonPoints) < 8 { // a valid polygon must have more than 2 points
- return false
- }
-
- // reference: nonzero winding rule, https://en.wikipedia.org/wiki/Nonzero-rule
- // split the plane into two by the check point horizontally:
- // y>0,includes (x>0 && y==0)
- // y<0,includes (x<0 && y==0)
- //
- // then scan every point in the polygon.
- //
- // if current point and previous point are in different planes (eg: curY>0 && prevY<0),
- // check the clock-direction from previous point to current point (use check point as origin).
- // if the direction is clockwise, then r++, otherwise then r--
- // finally, if 2==abs(r), then the check point is inside the polygon
-
- r := 0
- prevX, prevY := polygonPoints[0], polygonPoints[1]
- prev := (prevY > y) || ((prevX > x) && (prevY == y))
- for i := 2; i < len(polygonPoints); i += 2 {
- currX, currY := polygonPoints[i], polygonPoints[i+1]
- curr := (currY > y) || ((currX > x) && (currY == y))
-
- if curr == prev {
- prevX, prevY = currX, currY
- continue
- }
-
- if mul := (prevX-x)*(currY-y) - (currX-x)*(prevY-y); mul >= 0 {
- r++
- } else { // mul < 0
- r--
- }
- prevX, prevY = currX, currY
- prev = curr
- }
-
- return r == 2 || r == -2
- }
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