common: Use Z=0 for Inferno.ConvexHull2D()

+ Test

Author: markus-wa

common/inferno.go

@@ -60,7 +60,7 @@ func (inf Inferno) ConvexHull2D() *s2.Loop {
 			Vector: r3.Vector{
 				X: f.Vector.X,
 				Y: f.Vector.Y,
-				Z: 1,
+				Z: 0,
 			},
 		})
 	}

common/inferno_test.go

@@ -4,6 +4,7 @@ import (
 	"testing"
 
 	r3 "github.com/golang/geo/r3"
+	s2 "github.com/golang/geo/s2"
 	assert "github.com/stretchr/testify/assert"
 )
 
@@ -37,3 +38,43 @@ func TestInfernoActive(t *testing.T) {
 
 	assert.Equal(t, activeFires, inf.Active().Fires, "Active inferno should contain active fires")
 }
+
+func TestInfernoConvexHull2D(t *testing.T) {
+	// Construct a  Inferno that looks roughly like this.
+	// D should be inside the 2D Convex Hull but a corner of the 3D Convex Hull
+	//
+	//         C
+	//       /   \
+	//     /   D   \
+	//   /           \
+	// A - - - - - - - B
+	//
+	inf := Inferno{
+		Fires: []*Fire{
+			&Fire{
+				Vector: r3.Vector{X: 1, Y: 2, Z: 3},
+			},
+			&Fire{
+				Vector: r3.Vector{X: 4, Y: 7, Z: 6},
+			},
+			&Fire{
+				Vector: r3.Vector{X: 7, Y: 2, Z: 9},
+			},
+			&Fire{
+				Vector: r3.Vector{X: 4, Y: 4, Z: 12}, // This fire is inside the 2D hull
+			},
+		},
+	}
+
+	expectedHull := s2.LoopFromPoints([]s2.Point{
+		s2.Point{Vector: r3.Vector{X: 4, Y: 7, Z: 0}},
+		s2.Point{Vector: r3.Vector{X: 1, Y: 2, Z: 0}},
+		s2.Point{Vector: r3.Vector{X: 7, Y: 2, Z: 0}},
+	})
+
+	assert.ElementsMatch(t, expectedHull.Vertices(), inf.ConvexHull2D().Vertices(), "ConvexHull2D should be as expected")
+	assert.True(t, inf.ConvexHull2D().BoundaryEqual(expectedHull), "Boundary of expected and actual should be equal")
+
+	// 3D-hull should be different
+	assert.NotEqual(t, expectedHull.NumVertices(), inf.ConvexHull3D().NumVertices(), "3D hull should contain the vertex 'D'")
+}