UnrealPrototyping/Tools/Terrain/internal/plates/paint_test.go

package plates

import (
	"math"
	"testing"
)

// A painted layer and its legend, built by hand: two plates split at a quarter and three quarters of the way
// round, driven into each other along X with no spin.
func paintedStripes(w, h int) ([]uint8, *PaintLegend) {
	lg := &PaintLegend{
		WarnDistance: 60,
		Plates: []PaintPlate{
			{Name: "west", RGB: [3]int{200, 60, 60}, SpeedCmYr: 2, HeadingDeg: 90},  // due east
			{Name: "east", RGB: [3]int{60, 60, 200}, SpeedCmYr: 2, HeadingDeg: 270}, // due west
		},
	}
	px := make([]uint8, w*h*3)
	for y := range h {
		for x := range w {
			id := 0
			if x >= w/4 && x < 3*w/4 {
				id = 1
			}
			o := (y*w + x) * 3
			c := lg.Plates[id].RGB
			px[o], px[o+1], px[o+2] = uint8(c[0]), uint8(c[1]), uint8(c[2])
		}
	}
	return px, lg
}

func TestAPaintedLayerBecomesAPlanet(t *testing.T) {
	p := testPlanet(t)
	px, lg := paintedStripes(400, 200)

	m, match, err := FromPainting(p, Default(), lg, px, 400, 200, allLandAt)
	if err != nil {
		t.Fatalf("from painting: %v", err)
	}
	if match.Far != 0 {
		t.Errorf("%d of %d sampled cells did not match a plate colour", match.Far, match.Cells)
	}
	if len(m.Plates) != 2 {
		t.Fatalf("%d plates from a two-colour legend", len(m.Plates))
	}
	if len(m.Boundaries) != 2 {
		t.Fatalf("%d boundaries; two stripes on a cylinder make two contacts", len(m.Boundaries))
	}

	// The same invariant the generated path has: with a pure translation one margin closes and the other
	// opens, by the same amount. Two plates at 2 cm/yr closing head-on give 4 cm/yr.
	means := sortedMeans(m.Boundaries)
	if means[0] >= 0 || means[1] <= 0 {
		t.Fatalf("closing rates %.4g and %.4g; one of each is the only arrangement possible", means[0], means[1])
	}
	if got := math.Abs(means[1]); math.Abs(got-0.04) > 1e-3 {
		t.Errorf("painted plates at 2 cm/yr each close at %.4g m/yr, want 0.04", got)
	}
	// Both painted as land, so both are continental and the closing margin is a collision.
	if got, want := kinds(m.Boundaries), []string{"collision", "rift"}; !sameStrings(got, want) {
		t.Errorf("got %v, want %v", got, want)
	}
}

func allLandAt(xM, yM float64) bool { return true }

func TestAHeadingIsACompassBearing(t *testing.T) {
	p := testPlanet(t)
	px, lg := paintedStripes(400, 200)
	// 0 points at the top of the image, which is -Y; 90 to the right, which is +X.
	lg.Plates[0].HeadingDeg = 0
	lg.Plates[1].HeadingDeg = 90

	m, _, err := FromPainting(p, Default(), lg, px, 400, 200, allLandAt)
	if err != nil {
		t.Fatalf("from painting: %v", err)
	}
	north, east := m.Plates[0], m.Plates[1]
	if math.Abs(north.TransXM) > 1e-9 || north.TransYM >= 0 {
		t.Errorf("heading 0 gives (%.4g, %.4g); it should point at the top of the map",
			north.TransXM, north.TransYM)
	}
	if math.Abs(east.TransYM) > 1e-9 || east.TransXM <= 0 {
		t.Errorf("heading 90 gives (%.4g, %.4g); it should point to the right of the map",
			east.TransXM, east.TransYM)
	}
	if got := math.Hypot(east.TransXM, east.TransYM); math.Abs(got-0.02) > 1e-9 {
		t.Errorf("2 cm/yr came out as %.4g m/yr", got)
	}
}

func TestThePaintingCanOverruleTheLandMask(t *testing.T) {
	p := testPlanet(t)
	px, lg := paintedStripes(400, 200)

	// Every cell is land, so both plates are continental and the closing margin is a collision.
	m, _, err := FromPainting(p, Default(), lg, px, 400, 200, allLandAt)
	if err != nil {
		t.Fatalf("from painting: %v", err)
	}
	if !m.Plates[0].Continental || !m.Plates[1].Continental {
		t.Fatal("a planet of land has an oceanic plate on it")
	}

	// The legend says otherwise about one of them, and a legend that bothers to say so wins.
	oceanic := false
	lg.Plates[1].Continental = &oceanic
	m, _, err = FromPainting(p, Default(), lg, px, 400, 200, allLandAt)
	if err != nil {
		t.Fatalf("from painting: %v", err)
	}
	if m.Plates[1].Continental {
		t.Error("the legend called plate 1 oceanic and the land mask overruled it")
	}
	// And the consequence is the point of the override: the same margin is now a subduction zone.
	if got, want := kinds(m.Boundaries), []string{"ridge", "subduction"}; !sameStrings(got, want) {
		t.Errorf("got %v, want %v", got, want)
	}
}

func TestACentroidIsMeasuredTheShortWayRound(t *testing.T) {
	p := testPlanet(t)
	const w, h = 400, 200
	lg := &PaintLegend{
		WarnDistance: 60,
		Plates: []PaintPlate{
			{Name: "seam", RGB: [3]int{200, 60, 60}, SpeedCmYr: 2, HeadingDeg: 90},
			{Name: "rest", RGB: [3]int{60, 60, 200}, SpeedCmYr: 2, HeadingDeg: 270},
		},
	}
	// Plate 0 is painted across the meridian: the left eighth and the right eighth of the image. Its centre
	// is the seam, and an arithmetic mean of those columns would put it on the far side of the planet - and
	// with it the pole it spins about.
	px := make([]uint8, w*h*3)
	for y := range h {
		for x := range w {
			id := 1
			if x < w/8 || x >= 7*w/8 {
				id = 0
			}
			o := (y*w + x) * 3
			c := lg.Plates[id].RGB
			px[o], px[o+1], px[o+2] = uint8(c[0]), uint8(c[1]), uint8(c[2])
		}
	}

	m, _, err := FromPainting(p, Default(), lg, px, w, h, allLandAt)
	if err != nil {
		t.Fatalf("from painting: %v", err)
	}
	circ := p.CircumferenceM()
	got := m.Plates[0].SiteXM
	// Near the meridian, measured the short way round: either just above 0 or just below the circumference.
	if d := math.Abs(wrapDelta(got, circ)); d > circ/16 {
		t.Errorf("the seam-straddling plate's centre is at %.0f m of %.0f; it should be near the meridian, "+
			"and the arithmetic mean would have put it near %.0f", got, circ, circ/2)
	}
}

func TestAProposalReadsBackAsTheSamePlanet(t *testing.T) {
	p := testPlanet(t)
	cfg := Default()
	cfg.Count = 6
	land := func(xM, yM float64) bool { return yM > 4000 && yM < 14000 }

	made, err := Build(p, 3630, cfg, land)
	if err != nil {
		t.Fatalf("build: %v", err)
	}

	// The round trip is what makes Propose worth having: what it writes has to be a layer that comes back as
	// the planet it was written from, or an author's first edit starts from something that was never true.
	px, w, h, lg := made.Propose(1600)
	read, match, err := FromPainting(p, cfg, lg, px, w, h, land)
	if err != nil {
		t.Fatalf("read back: %v", err)
	}
	if match.Far != 0 {
		t.Errorf("%d of %d cells of its own proposal did not match its own legend", match.Far, match.Cells)
	}
	if len(read.Plates) != len(made.Plates) {
		t.Fatalf("%d plates written, %d read back", len(made.Plates), len(read.Plates))
	}

	// The motions survive the trip through the legend's cm/yr and degrees. Rounded when written - a tenth of
	// a cm/yr and a whole degree - so the tolerance is the rounding, not a fudge.
	for i := range made.Plates {
		a, b := made.Plates[i], read.Plates[i]
		if d := math.Hypot(a.TransXM-b.TransXM, a.TransYM-b.TransYM); d > 0.0006 {
			t.Errorf("plate %d drifts %.5g m/yr differently after the round trip", i, d)
		}
		if a.Continental != b.Continental {
			t.Errorf("plate %d was %v continental and reads back %v", i, a.Continental, b.Continental)
		}
	}

	// And the tectonics: the same margins doing the same things. Not vertex-for-vertex - the proposal is a
	// raster at 1600 px and the model was traced at the tectonic grid - but the same boundaries by count and
	// by what each one is.
	if len(read.Boundaries) != len(made.Boundaries) {
		t.Errorf("%d boundaries written, %d read back", len(made.Boundaries), len(read.Boundaries))
	}
	if got, want := kinds(read.Boundaries), kinds(made.Boundaries); !sameStrings(got, want) {
		t.Errorf("margins read back as %v, were %v", got, want)
	}
}

func TestALegendThatCannotBeAPlanetIsRefused(t *testing.T) {
	one := &PaintLegend{Plates: []PaintPlate{{Name: "only", RGB: [3]int{1, 2, 3}}}}
	if err := one.validate("test"); err == nil {
		t.Error("a planet in one plate was accepted; it has no boundaries")
	}
	dup := &PaintLegend{Plates: []PaintPlate{
		{Name: "a", RGB: [3]int{1, 2, 3}},
		{Name: "b", RGB: [3]int{1, 2, 3}},
	}}
	if err := dup.validate("test"); err == nil {
		t.Error("two plates sharing a colour were accepted; a colour is one plate")
	}
}