From c44b03cfddbbee5e6ea15ecabd2204a9b1be1258 Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Sun, 14 Apr 2019 16:49:01 +0900
Subject: [PATCH] Bug fix: Add vector/internal/math

---
 vector/internal/math/math.go      | 56 +++++++++++++++++++++++++++++++
 vector/internal/math/math_test.go | 47 ++++++++++++++++++++++++++
 2 files changed, 103 insertions(+)
 create mode 100644 vector/internal/math/math.go
 create mode 100644 vector/internal/math/math_test.go

diff --git a/vector/internal/math/math.go b/vector/internal/math/math.go
new file mode 100644
index 000000000..9a8e27fa0
--- /dev/null
+++ b/vector/internal/math/math.go
@@ -0,0 +1,56 @@
+// Copyright 2019 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package math
+
+import (
+	"math"
+)
+
+type Point struct {
+	X float32
+	Y float32
+}
+
+type Vec2 struct {
+	X float32
+	Y float32
+}
+
+func (p Vec2) Cross(other Vec2) float32 {
+	return p.X*other.Y - p.Y*other.X
+}
+
+type Segment struct {
+	P0 Point
+	P1 Point
+}
+
+func (s Segment) Translate(offset float32) Segment {
+	a := math.Atan2(float64(s.P1.Y-s.P0.Y), float64(s.P1.X-s.P0.X))
+	si, co := math.Sincos(a + math.Pi/2)
+	dx, dy := float32(co)*offset, float32(si)*offset
+	return Segment{
+		P0: Point{s.P0.X + dx, s.P0.Y + dy},
+		P1: Point{s.P1.X + dx, s.P1.Y + dy},
+	}
+}
+
+func (s Segment) IntersectionAsLines(other Segment) Point {
+	v1 := Vec2{other.P1.X - other.P0.X, other.P1.Y - other.P0.Y}
+	d0 := v1.Cross(Vec2{s.P0.X - other.P0.X, s.P0.Y - other.P0.Y})
+	d1 := -v1.Cross(Vec2{s.P1.X - other.P1.X, s.P1.Y - other.P1.Y})
+	t := d0 / (d0 + d1)
+	return Point{s.P0.X + (s.P1.X-s.P0.X)*t, s.P0.Y + (s.P1.Y-s.P0.Y)*t}
+}
diff --git a/vector/internal/math/math_test.go b/vector/internal/math/math_test.go
new file mode 100644
index 000000000..81eb72379
--- /dev/null
+++ b/vector/internal/math/math_test.go
@@ -0,0 +1,47 @@
+// Copyright 2019 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package math_test
+
+import (
+	"testing"
+
+	. "github.com/hajimehoshi/ebiten/vector/internal/math"
+)
+
+func TestIntersectionAsLine(t *testing.T) {
+	cases := []struct {
+		S0   Segment
+		S1   Segment
+		Want Point
+	}{
+		{
+			S0:   Segment{Point{0.5, 0}, Point{0.5, 0.5}},
+			S1:   Segment{Point{1, 1}, Point{2, 1}},
+			Want: Point{0.5, 1},
+		},
+		{
+			S0:   Segment{Point{0.5, 0}, Point{0.5, 1.5}},
+			S1:   Segment{Point{1, 1}, Point{2, 1}},
+			Want: Point{0.5, 1},
+		},
+	}
+	for _, c := range cases {
+		got := c.S0.IntersectionAsLines(c.S1)
+		want := c.Want
+		if got != want {
+			t.Errorf("got: %v, want: %v", got, want)
+		}
+	}
+}