Added: Initial world generation tool

Tools/Terrain/internal/fluvial/repose_test.go

@@ -0,0 +1,50 @@
+package fluvial
+
+import (
+	"math"
+	"testing"
+)
+
+// TestClampToReposeCutsACone is the smallest possible check on the constraint: a cone far steeper than the
+// repose angle must come back at or under it.
+func TestClampToReposeCutsACone(t *testing.T) {
+	const (
+		w, h  = 81, 81
+		cellM = 10.0
+		talus = 0.4 // about 22 degrees
+	)
+	base := make([]bool, w*h)
+	field := make([]float32, w*h)
+	for y := 0; y < h; y++ {
+		for x := 0; x < w; x++ {
+			d := math.Hypot(float64(x-w/2), float64(y-h/2)) * cellM
+			field[y*w+x] = float32(math.Max(0, 800-2.0*d)) // slope 2.0, five times repose
+		}
+	}
+	g := NewGrid(w, h, cellM, base)
+	g.SetElevationRange(-100, 2000)
+	removed := g.ClampToRepose(field, talus)
+
+	worst := 0.0
+	for y := 0; y < h; y++ {
+		for x := 0; x < w; x++ {
+			for k := 0; k < 8; k++ {
+				nx, ny := x+dx8[k], y+dy8[k]
+				if nx < 0 || ny < 0 || nx >= w || ny >= h {
+					continue
+				}
+				d := cellM
+				if dx8[k] != 0 && dy8[k] != 0 {
+					d = cellM * math.Sqrt2
+				}
+				if s := float64(field[y*w+x]-field[ny*w+nx]) / d; s > worst {
+					worst = s
+				}
+			}
+		}
+	}
+	t.Logf("removed %.2f m mean; steepest slope now %.3f (repose %.3f)", removed, worst, talus)
+	if worst > talus*1.02 {
+		t.Errorf("steepest slope %.3f exceeds repose %.3f", worst, talus)
+	}
+}