box.go

func CreateMesh() *model3d.Mesh {
	box := model3d.NewMesh()

	stepSize := 0.05
	addQuad := func(p model3d.Coord3D, normalAxis int) {
		ax1 := model3d.Coord3D{X: stepSize}
		ax2 := model3d.Coord3D{Y: stepSize}
		if normalAxis == 0 {
			ax1 = model3d.Coord3D{Z: stepSize}
		} else if normalAxis == 1 {
			ax2 = model3d.Coord3D{Z: stepSize}
		}
		box.Add(&model3d.Triangle{p, p.Add(ax1), p.Add(ax2)})
		box.Add(&model3d.Triangle{p.Add(ax1), p.Add(ax2), p.Add(ax1).Add(ax2)})
	}

	// All but top two faces.
	for x := -20; x < 20; x += 5 {
		for z := -50; z < 50; z += 5 {
			fx := float64(x) / 100
			fz := float64(z) / 100
			for _, fy := range []float64{-0.2, 0.2} {
				addQuad(model3d.Coord3D{X: fx, Y: fy, Z: fz}, 1)
				addQuad(model3d.Coord3D{X: fy, Y: fx, Z: fz}, 0)
			}
		}
	}

	// Top two faces.
	for x := -20; x < 20; x += 5 {
		for y := -20; y < 20; y += 5 {
			fx := float64(x) / 100
			fy := float64(y) / 100
			addQuad(model3d.Coord3D{X: fx, Y: fy, Z: -0.5}, 2)
			addQuad(model3d.Coord3D{X: fx, Y: fy, Z: 0.5}, 2)
		}
	}

	// I got really lazy here, so now let's make the
	// mesh manifold and oriented.
	box = box.Repair(1e-8)
	box, _ = box.RepairNormals(1e-8)

	// Don't let the box face the camera head on,
	// allowing us to see more detail.
	rotate := model3d.NewMatrix3Rotation(model3d.Coord3D{Z: 1}, 0.4)
	rotate[8] = 2
	return box.MapCoords(rotate.MulColumn).FlipDelaunay()
}