Tooling

Tools/Terrain/internal/detail/classes.go

@@ -0,0 +1,50 @@
+package detail
+
+// Classes is what the painted class asks of the detail passes, per cell, already blended.
+//
+// It exists because two classes can have the same uplift rate and the same erodibility - which is everything
+// the geology grid knows about them - and still be completely different ground. A desert and a wet lowland
+// are both "low, slowly rising"; what separates them is at two metres, in how much running water crosses
+// them, how sharp their ledges stay and how much of them is dune.
+//
+// **Four fields rather than a class index and a lookup table**, which is what this was. The index is the
+// right thing to carry - a class is a name, and a name is never interpolated - but the *numbers* it stands
+// for are quantities, and quantities interpolate. Kept as a lookup, a desert meeting a lowland changed from
+// seven metres of dune amplitude to two in the width of one cell, along a line the painter drew with a mouse,
+// and it read exactly as what it was: a boundary in a picture rather than a change in the ground. Blended,
+// the same boundary is a few hundred metres of one becoming the other, which is what the edge of a sand sea
+// looks like from the ground.
+//
+// The blending happens where the fields are built (see planet.blendedClasses), because that is where the
+// class raster and the tile's margin both are; by the time a pass reads one it is just a number per cell.
+//
+// Nil means every cell uses the pipeline's own numbers, which is what happens on a template whose legend
+// overrides nothing.
+type Classes struct {
+	Droplets []float32 // per cell: droplets a cell spawns
+	AmpLo    []float32 // per cell: detail noise amplitude on flat ground
+	AmpHi    []float32 // per cell: and on steep ground
+	Contrast []float32 // per cell: strata hardness contrast
+}
+
+// droplets, amp and contrast read a cell, falling back to the uniform value when there is no table.
+func (c *Classes) droplets(i int, def float64) float64 {
+	if c == nil || c.Droplets == nil {
+		return def
+	}
+	return float64(c.Droplets[i])
+}
+
+func (c *Classes) amp(i int, defLo, defHi float64) (float64, float64) {
+	if c == nil || c.AmpLo == nil {
+		return defLo, defHi
+	}
+	return float64(c.AmpLo[i]), float64(c.AmpHi[i])
+}
+
+func (c *Classes) contrast(i int, def float64) float64 {
+	if c == nil || c.Contrast == nil {
+		return def
+	}
+	return float64(c.Contrast[i])
+}