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-rw-r--r--modules/avatar/identicon/polygon.go68
1 files changed, 68 insertions, 0 deletions
diff --git a/modules/avatar/identicon/polygon.go b/modules/avatar/identicon/polygon.go
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+++ b/modules/avatar/identicon/polygon.go
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+// Copyright 2021 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+// 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, 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
+}