vector: bug fix: isPointCloseToSegment didn't work when two p0 and p1 are the same

Closes #3061

vector/export_test.go

@@ -0,0 +1,32 @@
+// Copyright 2024 The Ebitengine 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 vector
+
+type Point struct {
+	X, Y float32
+}
+
+func IsPointCloseToSegment(p, p0, p1 Point, allow float32) bool {
+	return isPointCloseToSegment(point{
+		x: p.X,
+		y: p.Y,
+	}, point{
+		x: p0.X,
+		y: p0.Y,
+	}, point{
+		x: p1.X,
+		y: p1.Y,
+	}, allow)
+}

vector/path.go

@@ -232,12 +232,17 @@ func lineForTwoPoints(p0, p1 point) (a, b, c float32) {
 }
 
 // isPointCloseToSegment detects the distance between a segment (x0, y0)-(x1, y1) and a point (x, y) is less than allow.
+// If p0 and p1 are the same, isPointCloseToSegment returns true when the distance between p0 and p is less than allow.
 func isPointCloseToSegment(p, p0, p1 point, allow float32) bool {
+	if p0 == p1 {
+		return allow*allow >= (p0.x-p.x)*(p0.x-p.x)+(p0.y-p.y)*(p0.y-p.y)
+	}
+
 	a, b, c := lineForTwoPoints(p0, p1)
 
 	// The distance between a line ax+by+c=0 and (x0, y0) is
 	//     |ax0 + by0 + c| / √(a² + b²)
-	return allow*allow*(a*a+b*b) > (a*p.x+b*p.y+c)*(a*p.x+b*p.y+c)
+	return allow*allow*(a*a+b*b) >= (a*p.x+b*p.y+c)*(a*p.x+b*p.y+c)
 }
 
 // crossingPointForTwoLines returns a crossing point for two lines.

vector/path_test.go

@@ -0,0 +1,88 @@
+// Copyright 2024 The Ebitengine 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 vector_test
+
+import (
+	"testing"
+
+	"github.com/hajimehoshi/ebiten/v2/vector"
+)
+
+func TestIsPointCloseToSegment(t *testing.T) {
+	testCases := []struct {
+		p     vector.Point
+		p0    vector.Point
+		p1    vector.Point
+		allow float32
+		want  bool
+	}{
+		{
+			p:     vector.Point{0.5, 0.5},
+			p0:    vector.Point{0, 0},
+			p1:    vector.Point{1, 0},
+			allow: 1,
+			want:  true,
+		},
+		{
+			p:     vector.Point{0.5, 1.5},
+			p0:    vector.Point{0, 0},
+			p1:    vector.Point{1, 0},
+			allow: 1,
+			want:  false,
+		},
+		{
+			p:     vector.Point{0.5, 0.5},
+			p0:    vector.Point{0, 0},
+			p1:    vector.Point{1, 1},
+			allow: 0,
+			want:  true,
+		},
+		{
+			p:     vector.Point{0, 1},
+			p0:    vector.Point{0, 0},
+			p1:    vector.Point{1, 1},
+			allow: 0.7,
+			want:  false,
+		},
+		{
+			p:     vector.Point{0, 1},
+			p0:    vector.Point{0, 0},
+			p1:    vector.Point{1, 1},
+			allow: 0.8,
+			want:  true,
+		},
+		{
+			// p0 and p1 are the same.
+			p:     vector.Point{0, 1},
+			p0:    vector.Point{0.5, 0.5},
+			p1:    vector.Point{0.5, 0.5},
+			allow: 0.7,
+			want:  false,
+		},
+		{
+			// p0 and p1 are the same.
+			p:     vector.Point{0, 1},
+			p0:    vector.Point{0.5, 0.5},
+			p1:    vector.Point{0.5, 0.5},
+			allow: 0.8,
+			want:  true,
+		},
+	}
+	for _, tc := range testCases {
+		if got := vector.IsPointCloseToSegment(tc.p, tc.p0, tc.p1, tc.allow); got != tc.want {
+			t.Errorf("got: %v, want: %v", got, tc.want)
+		}
+	}
+}