From ab32a830e6e7430ddc2f092df8fc57e7fa69d286 Mon Sep 17 00:00:00 2001
From: surdeus <surdeus@gmail.com>
Date: Tue, 30 May 2023 13:12:11 +0300
Subject: [PATCH] Implemented checking whether point is in triangle.

---
 src/cmd/math/main.go |  9 ++++++---
 src/gx/line.go       |  9 +++++++++
 src/gx/math.go       | 13 +++++++++++++
 src/gx/rect.go       |  4 ++++
 src/gx/triangle.go   | 32 ++++++++++++++------------------
 5 files changed, 46 insertions(+), 21 deletions(-)

diff --git a/src/cmd/math/main.go b/src/cmd/math/main.go
index d70acc1..bcaac25 100644
--- a/src/cmd/math/main.go
+++ b/src/cmd/math/main.go
@@ -34,7 +34,8 @@ func main() {
 	}.Line()
 	fmt.Println(l1.Crosses(l2))
 	fmt.Println(l1.ContainsPoint(gx.Point{1, 4}))
-	/*t := gx.Triangle{
+	
+	t := gx.Triangle{
 		gx.Point{0, 0},
 		gx.Point{0, 100},
 		gx.Point{100, 0},
@@ -42,6 +43,8 @@ func main() {
 	
 	points := []gx.Point{
 		gx.Point{},
+		gx.Point{100, 0},
+		gx.Point{0, 100},
 		gx.Point{.1, .1},
 		gx.Point{-1, -1},
 		gx.Point{1, 1},
@@ -51,8 +54,8 @@ func main() {
 	}
 	
 	for _, p := range points {
-		fmt.Println(p, t.PointIsIn(p))
-	}*/
+		fmt.Println(t, p, t.ContainsPoint(p))
+	}
 }
 
 
diff --git a/src/gx/line.go b/src/gx/line.go
index e5285a6..8269c5c 100644
--- a/src/gx/line.go
+++ b/src/gx/line.go
@@ -62,6 +62,15 @@ func (l1 Line) crossesLine(l2 Line) (Point, bool) {
 	return Point{x, y}, true
 }
 
+func (l LineSegment) ContainsPoint(p Point) bool {
+	line := l.Line()
+	if !line.ContainsPoint(p) {
+		return false
+	}
+	
+	return false
+}
+
 // Get square of length of line segment.
 func (ls LineSegment) LenSqr() Float {
 	return Sqr(ls[0].X - ls[1].X) +
diff --git a/src/gx/math.go b/src/gx/math.go
index 97f73fa..0b4dec3 100644
--- a/src/gx/math.go
+++ b/src/gx/math.go
@@ -18,6 +18,18 @@ func Sqr(v Float) Float {
 	return v * v
 }
 
+func Sgn(v Float) Float {
+	if v > 0 {
+		return 1
+	}
+	
+	if v < 0 {
+		return -1
+	}
+	
+	return 0
+}
+
 func RadiansToDegrees(v Float) Float {
 	return v
 }
@@ -26,3 +38,4 @@ func DeegresToRadians(v Float) Float {
 	return v
 }
 
+
diff --git a/src/gx/rect.go b/src/gx/rect.go
index 8ade214..0252bcc 100644
--- a/src/gx/rect.go
+++ b/src/gx/rect.go
@@ -57,6 +57,10 @@ func (r Rectangle) Triangles() Triangles {
 	return img
 }*/
 
+func (r Rectangle) ContainsPoint(p Point) bool {
+	return false
+}
+
 func NewImage(w, h int) (*Image) {
 	return ebiten.NewImage(w, h)
 }
diff --git a/src/gx/triangle.go b/src/gx/triangle.go
index 4a1e133..e1e5bac 100644
--- a/src/gx/triangle.go
+++ b/src/gx/triangle.go
@@ -39,27 +39,23 @@ func (t Triangle) SideLengthSquares() ([3]Float) {
 }
 
 // Check whether the point is in the triangle.
-func (t Triangle) PointIsIn(p Point) bool {
-	sls := t.SideLengthSquares()
+func (t Triangle) ContainsPoint(p Point) bool {
+	d1 := Triangle{p, t[0], t[1]}.Sgn()
+	d2 := Triangle{p, t[1], t[2]}.Sgn()
+	d3 := Triangle{p, t[2], t[0]}.Sgn()
 	
-	sl0 := LineSegment{p, t[0]}.LenSqr()
-	sl1 := LineSegment{p, t[1]}.LenSqr()
-	sl2 := LineSegment{p, t[2]}.LenSqr()
+	neg := (d1 < 0) || (d2 < 0) || (d3 < 0)
+	pos := (d1 > 0) || (d2 > 0) || (d3 > 0)
 	
-	if sl0 > sls[0] || sl0 > sls[2] {
-		return false
-	}
-	
-	if sl1 > sls[0] || sl1 > sls[1] {
-		return false
-	}
-	
-	if sl2 > sls[1] || sl2 > sls[2] {
-		return false
-	}
-	
-	return true
+	return !(neg && pos)
 }
+
+func (t Triangle) Sgn() Float {
+	return (t[0].X - t[2].X) * (t[1].Y - t[2].Y)  -
+		(t[1].X - t[2].X) * (t[0].Y - t[2].Y)
+}
+
+//func (t Triangle)
 /*
 func (r *DrawableRectangle) Draw(
 	e *Engine,