Tooling

Tools/Terrain/internal/planet/crater_test.go

@@ -0,0 +1,94 @@
+package planet
+
+import (
+	"math"
+	"testing"
+
+	"salty/terrain/internal/template"
+)
+
+// The profile is the whole of what a crater is, so it is worth pinning down: shore at sea level, a crest, an
+// inner wall, a floor, and nothing anywhere that is not monotonic on its own segment.
+func TestCraterProfileIsRimThenFloor(t *testing.T) {
+	c := template.Crater{RimM: 340, FloorM: 60, RimAt: 0.30, WallAt: 0.62}
+
+	if got := craterProfile(c, 0, 0); got != 0 {
+		t.Errorf("at the shore = %.1f m, want sea level: the island keeps the outline that was painted", got)
+	}
+	if got := craterProfile(c, 0, c.RimAt); math.Abs(got-c.RimM) > 1e-9 {
+		t.Errorf("at rim_at = %.1f m, want the rim %.1f", got, c.RimM)
+	}
+	if got := craterProfile(c, 0, c.WallAt); math.Abs(got-c.FloorM) > 1e-9 {
+		t.Errorf("at wall_at = %.1f m, want the floor %.1f", got, c.FloorM)
+	}
+	if got := craterProfile(c, 0, 1); got != c.FloorM {
+		t.Errorf("at the centre = %.1f m, want the floor %.1f", got, c.FloorM)
+	}
+
+	// Rising to the crest, falling to the floor, and the floor is dry.
+	prev := craterProfile(c, 0, 0)
+	for i := 1; i <= 30; i++ {
+		v := craterProfile(c, 0, c.RimAt*float64(i)/30)
+		if v < prev-1e-9 {
+			t.Fatalf("the outer flank dips at t = %.3f", c.RimAt*float64(i)/30)
+		}
+		prev = v
+	}
+	prev = craterProfile(c, 0, c.RimAt)
+	for i := 1; i <= 30; i++ {
+		v := craterProfile(c, 0, c.RimAt+(c.WallAt-c.RimAt)*float64(i)/30)
+		if v > prev+1e-9 {
+			t.Fatalf("the inner wall rises at t = %.3f", c.RimAt+(c.WallAt-c.RimAt)*float64(i)/30)
+		}
+		prev = v
+	}
+	if c.FloorM <= 0 {
+		t.Error("this crater's floor is not above sea level, which is what was asked for")
+	}
+}
+
+// A blob is normalised by its own widest point, so the same numbers describe a small crater and a large one.
+func TestCraterComponentsMeasureEachBlobsOwnRadius(t *testing.T) {
+	const w, h = 40, 12
+	mask := make([]bool, w*h)
+	dist := make([]float64, w*h)
+	set := func(x0, y0, wid, hei int, d float64) {
+		for y := y0; y < y0+hei; y++ {
+			for x := x0; x < x0+wid; x++ {
+				mask[y*w+x] = true
+				dist[y*w+x] = d
+			}
+		}
+	}
+	set(2, 2, 6, 6, 3)    // a blob whose widest point is 3
+	set(20, 4, 4, 4, 1.5) // and a smaller one at 1.5
+	wrap := func(x int) int { return ((x % w) + w) % w }
+
+	comp, maxDist, n := craterComponents(mask, dist, w, h, wrap)
+	if n != 2 {
+		t.Fatalf("found %d blobs, want 2", n)
+	}
+	a := maxDist[comp[3*w+3]]
+	b := maxDist[comp[5*w+21]]
+	if a != 3 || b != 1.5 {
+		t.Errorf("radii %.1f and %.1f, want 3 and 1.5", a, b)
+	}
+}
+
+// A crater on the seam is one crater, not two half craters with two different radii.
+func TestACraterOnTheSeamIsOneBlob(t *testing.T) {
+	const w, h = 40, 12
+	mask := make([]bool, w*h)
+	dist := make([]float64, w*h)
+	for y := 4; y < 8; y++ {
+		for _, x := range []int{38, 39, 0, 1} {
+			mask[y*w+x] = true
+			dist[y*w+x] = 2
+		}
+	}
+	wrap := func(x int) int { return ((x % w) + w) % w }
+	_, _, n := craterComponents(mask, dist, w, h, wrap)
+	if n != 1 {
+		t.Fatalf("found %d blobs across the seam, want 1", n)
+	}
+}