added index to modules for easier custom logic

pkg/wfc/module.go

@@ -8,6 +8,7 @@ import (
 // Stalberg. A module is a possible tile that might exist at a slot in the wave
 // function grid. It can be thought of as a single state of a superposition.
 type Module struct {
+	Index       int             // The index of the module in the input tiles
 	Adjacencies [4]ConstraintId // Adjacency constraints for each direction
 	Image       image.Image     // The tile image for the module
 }

pkg/wfc/wave.go

@@ -69,7 +69,7 @@ func NewWithCustomConstraints(tiles []image.Image, width, height int, fn Constra
 
 	// Automatically generate adjacency constraints for each input tile.
 	for i, tile := range tiles {
-		module := Module{Image: tile}
+		module := Module{Index: i, Image: tile}
 		for _, d := range Directions {
 			module.Adjacencies[d] = fn(tile, d)
 		}