UnrealPrototyping/Tools/Terrain/internal/region/region_test.go

package region

import (
	"strings"
	"testing"

	"salty/terrain/internal/template"
	"salty/terrain/internal/world"
)

const legendJSON = `{"classes":[
	{"name":"sea","rgb":[0,0,255],"sea":true,"depth_m":100},
	{"name":"land","rgb":[0,255,0],"uplift_mm_yr":0.5}
]}`

// testMap builds a planet from a picture of its painted rows. '#' is land, '.' is sea; the polar pad of
// synthetic ocean is added above and below.
func testMap(t *testing.T, rows []string, pad int) *template.Map {
	t.Helper()
	l, err := template.Parse([]byte(legendJSON))
	if err != nil {
		t.Fatal(err)
	}
	w := len(rows[0])
	p := world.Planet{CellM: 1, W: w, H: len(rows) + 2*pad, PadY: pad, NoisePeriodM: float64(w)}
	if err := p.Validate(); err != nil {
		t.Fatal(err)
	}
	m := &template.Map{P: p, L: l, Class: make([]uint8, p.W*p.H), Sea: make([]bool, p.W*p.H)}
	for i := range m.Class {
		m.Class[i], m.Sea[i] = 0, true
	}
	for y, row := range rows {
		if len(row) != w {
			t.Fatalf("row %d is %d wide, want %d", y, len(row), w)
		}
		for x, r := range row {
			if r == '#' {
				i := (y+pad)*p.W + x
				m.Class[i], m.Sea[i] = 1, false
			}
		}
	}
	return m
}

// assertBordersAreWater is the invariant the whole solve depends on, and the direct analogue of
// TestBorderIsAlwaysOcean: a grid edge is an outlet, so land on one would freeze at its initial relief while
// the interior eroded out from under it.
func assertBordersAreWater(t *testing.T, part *Partition, m *template.Map) {
	t.Helper()
	for _, r := range part.Regions {
		_, land := part.Cut(m, r)
		for x := 0; x < r.Frame.W; x++ {
			if land[x] {
				t.Errorf("region %d: land on the top edge at column %d", r.ID, x)
			}
			if land[(r.Frame.H-1)*r.Frame.W+x] {
				t.Errorf("region %d: land on the bottom edge at column %d", r.ID, x)
			}
		}
		for y := 0; y < r.Frame.H; y++ {
			if land[y*r.Frame.W] {
				t.Errorf("region %d: land on the left edge at row %d", r.ID, y)
			}
			if land[y*r.Frame.W+r.Frame.W-1] {
				t.Errorf("region %d: land on the right edge at row %d", r.ID, y)
			}
		}
	}
}

// The crater island in the template this was written for straddles x = 0. If the partitioner split it in
// two, half of it would be solved against a shore that does not exist.
func TestSeamStraddlingLandmassIsOneRegion(t *testing.T) {
	m := testMap(t, []string{
		"#.........#",
		"#.........#",
		"...........",
	}, 2)
	part, err := Build(m, 2, 1)
	if err != nil {
		t.Fatal(err)
	}
	if len(part.Regions) != 1 {
		t.Fatalf("got %d regions, want 1: the landmass wraps", len(part.Regions))
	}
	r := part.Regions[0]
	if !r.Seam {
		t.Error("the region does not report that it straddles the seam")
	}
	if r.LandCells != 4 {
		t.Errorf("LandCells = %d, want 4", r.LandCells)
	}
	// Land occupies columns 10 and 0, which are neighbours on an 11-column cylinder; a 2-cell margin on
	// each side makes the frame six columns wide starting at column 8.
	if r.Frame.W != 6 {
		t.Errorf("frame width = %d, want 6", r.Frame.W)
	}
	if r.Frame.X0 != 8 {
		t.Errorf("frame X0 = %d, want 8", r.Frame.X0)
	}
	assertBordersAreWater(t, part, m)
}

// Landmasses close enough to shelter each other are solved together; further apart they are not. The
// alternative that was rejected - overlapping dilated bounding boxes - is transitively closed and one long
// landmass has an enormous box, so on a real template it collapses most of the map into a single region.
func TestClusteringFollowsDistanceNotBoundingBoxes(t *testing.T) {
	near := testMap(t, []string{
		"..............................",
		".####....#....................",
		".####....#....................",
		"..............................",
	}, 3)
	part, err := Build(near, 3, 1)
	if err != nil {
		t.Fatal(err)
	}
	if len(part.Regions) != 1 {
		t.Fatalf("got %d regions, want 1: a four-cell gap closes under a three-cell margin on each side",
			len(part.Regions))
	}

	far := testMap(t, []string{
		"..............................",
		".####.........#...............",
		".####.........#...............",
		"..............................",
	}, 3)
	part, err = Build(far, 3, 1)
	if err != nil {
		t.Fatal(err)
	}
	if len(part.Regions) != 2 {
		t.Fatalf("got %d regions, want 2: a nine-cell gap does not", len(part.Regions))
	}
	assertBordersAreWater(t, part, far)
}

func TestEveryRegionBorderIsWater(t *testing.T) {
	m := testMap(t, []string{
		"..###...........................................................",
		"..###.........####.............####.............##..............",
		"..............####.............####.............##..............",
		"..............####.............####.............................",
		"................................................................",
		"................................................................",
	}, 3)
	part, err := Build(m, 3, 1)
	if err != nil {
		t.Fatal(err)
	}
	if len(part.Regions) < 2 {
		t.Fatalf("got %d regions; the picture has several separate landmasses", len(part.Regions))
	}
	assertBordersAreWater(t, part, m)
}

// A polar cap touches the top row of the painted map. The synthetic ocean pad is what gives it a shore, so
// that fluvial.isOutlet - which treats every top-row cell as an outlet - is answering about water.
func TestAPolarCapGetsAMarginOfOcean(t *testing.T) {
	m := testMap(t, []string{
		"###############...............",
		"########......................",
		"..............................",
		"..............................",
	}, 3)
	part, err := Build(m, 3, 1)
	if err != nil {
		t.Fatal(err)
	}
	if len(part.Regions) != 1 {
		t.Fatalf("got %d regions, want 1", len(part.Regions))
	}
	r := part.Regions[0]
	if r.Frame.Y0 != 0 {
		t.Errorf("frame Y0 = %d, want 0: the cap reaches into the pad", r.Frame.Y0)
	}
	assertBordersAreWater(t, part, m)
}

// Every painted land cell belongs to exactly one region, and a round trip through Cut and Composite
// reproduces it. If two regions owned the same cell, one would silently overwrite the other.
func TestCutAndCompositeCoverEveryLandCellOnce(t *testing.T) {
	m := testMap(t, []string{
		"#..####...................#",
		"#..####...................#",
		"...........................",
		"..........##.....##........",
		"..........##.....##........",
		"...........................",
	}, 3)
	part, err := Build(m, 2, 1)
	if err != nil {
		t.Fatal(err)
	}
	if len(part.Regions) < 2 {
		t.Fatalf("got %d regions; the picture has several separate landmasses", len(part.Regions))
	}

	dst := make([]float32, m.P.W*m.P.H)
	hits := make([]int, len(dst))
	total := 0
	for _, r := range part.Regions {
		_, land := part.Cut(m, r)
		src := make([]float32, r.Frame.Cells())
		for i := range src {
			if land[i] {
				src[i] = float32(r.ID + 1)
			}
		}
		total += part.Composite(dst, m, r, src)
		for y := 0; y < r.Frame.H; y++ {
			for x := 0; x < r.Frame.W; x++ {
				pi := r.Frame.PlanetIdx(x, y)
				if part.Owner[pi] == int32(r.ID) && !m.Sea[pi] {
					hits[pi]++
				}
			}
		}
	}

	painted := 0
	for i := range m.Sea {
		if !m.Sea[i] {
			painted++
		}
	}
	if total != painted {
		t.Errorf("composited %d land cells, but %d are painted", total, painted)
	}
	for i, n := range hits {
		if m.Sea[i] {
			if n != 0 {
				t.Fatalf("water cell %d was written %d times", i, n)
			}
			continue
		}
		if n != 1 {
			t.Fatalf("land cell %d was written %d times, want exactly 1", i, n)
		}
		if dst[i] == 0 {
			t.Fatalf("land cell %d came back zero", i)
		}
	}
}

// A landmass that rings the planet cannot be flattened into a rectangle with water on both sides, and the
// solve needs that. Better a clear refusal than a silently frozen coastline.
func TestALandmassRingingThePlanetIsRefused(t *testing.T) {
	m := testMap(t, []string{
		"##########",
		"..........",
		"..........",
		"..........",
	}, 2)
	_, err := Build(m, 2, 1)
	if err == nil {
		t.Fatal("accepted a landmass that goes all the way round")
	}
	if !strings.Contains(err.Error(), "all the way round") {
		t.Errorf("error %q does not say why", err)
	}
}

// A stray paint pixel should not cost a whole region.
func TestSpecksAreDroppedAndCounted(t *testing.T) {
	m := testMap(t, []string{
		"####......................",
		"####...............#......",
		"####......................",
		"..........................",
	}, 2)
	part, err := Build(m, 2, 4)
	if err != nil {
		t.Fatal(err)
	}
	if len(part.Regions) != 1 {
		t.Fatalf("got %d regions, want 1", len(part.Regions))
	}
	if part.DroppedRegions != 1 || part.DroppedCells != 1 {
		t.Errorf("dropped %d regions / %d cells, want 1 and 1", part.DroppedRegions, part.DroppedCells)
	}
	// And the speck is not owned by anything, so nothing solves it.
	for i := range m.Sea {
		if !m.Sea[i] && part.Owner[i] < 0 {
			return
		}
	}
	t.Error("the speck is still owned by a region")
}

func TestTheMarginMustFitInsideThePad(t *testing.T) {
	m := testMap(t, []string{"####......", ".........."}, 1)
	if _, err := Build(m, 4, 1); err == nil {
		t.Fatal("accepted a margin wider than the polar pad")
	}
}

func TestSpanWrapsTheShortWay(t *testing.T) {
	mark := func(w int, on ...int) []bool {
		c := make([]bool, w)
		for _, x := range on {
			c[x] = true
		}
		return c
	}
	cases := []struct {
		cols       []bool
		w          int
		x0, wanted int
	}{
		{mark(10, 0, 1, 2), 10, 0, 3},
		{mark(10, 8, 9, 0, 1), 10, 8, 4},
		{mark(10, 5), 10, 5, 1},
		{mark(10, 0, 5), 10, 5, 6},
	}
	for _, c := range cases {
		x0, w := span(c.cols, c.w)
		if x0 != c.x0 || w != c.wanted {
			t.Errorf("span = %d+%d, want %d+%d", x0, w, c.x0, c.wanted)
		}
	}
}