examples/2048: Implement the rule

examples/2048/2048/board.go

@@ -17,6 +17,7 @@ package twenty48
 import (
 	"fmt"
 	"math/rand"
+	"sort"
 
 	"github.com/hajimehoshi/ebiten"
 	"github.com/hajimehoshi/ebiten/ebitenutil"
@@ -66,20 +67,81 @@ func (b *Board) addRandomTile() bool {
 	return true
 }
 
+func tileAt(tiles map[*Tile]struct{}, x, y int) *Tile {
+	for t := range tiles {
+		if t.x == x && t.y == y {
+			return t
+		}
+	}
+	return nil
+}
+
+func (b *Board) tileAt(x, y int) *Tile {
+	return tileAt(b.tiles, x, y)
+}
+
 func (b *Board) Move(dir Dir) {
+	vx, vy := dir.Vector()
+	tx := []int{}
+	ty := []int{}
+	for i := 0; i < b.size; i++ {
+		tx = append(tx, i)
+		ty = append(ty, i)
+	}
+	if vx > 0 {
+		sort.Sort(sort.Reverse(sort.IntSlice(tx)))
+	}
+	if vy > 0 {
+		sort.Sort(sort.Reverse(sort.IntSlice(ty)))
+	}
+	nextTiles := map[*Tile]struct{}{}
+	merged := map[*Tile]bool{}
+	for _, j := range ty {
+		for _, i := range tx {
+			t := b.tileAt(i, j)
+			if t == nil {
+				continue
+			}
+			ii := i
+			jj := j
+			for {
+				ni := ii + vx
+				nj := jj + vy
+				if ni < 0 || ni >= b.size || nj < 0 || nj >= b.size {
+					break
+				}
+				tt := b.tileAt(ni, nj)
+				if tt == nil {
+					ii = ni
+					jj = nj
+					continue
+				}
+				nt := tileAt(nextTiles, ni, nj)
+				if t.value == tt.value && (nt == nil || !merged[nt]) {
+					ii = ni
+					jj = nj
+				}
+				break
+			}
+			if tt := b.tileAt(ii, jj); tt != t && tt != nil {
+				t.value += tt.value
+				merged[t] = true
+				delete(nextTiles, tt)
+			}
+			t.x = ii
+			t.y = jj
+			nextTiles[t] = struct{}{}
+		}
+	}
+	b.tiles = nextTiles
 	b.addRandomTile()
 }
 
 func (b *Board) Draw(screen *ebiten.Image) error {
-	posToTile := map[int]*Tile{}
-	for t := range b.tiles {
-		i := t.x + t.y*b.size
-		posToTile[i] = t
-	}
 	str := ""
 	for j := 0; j < b.size; j++ {
 		for i := 0; i < b.size; i++ {
-			t := posToTile[i+j*b.size]
+			t := b.tileAt(i, j)
 			if t != nil {
 				str += fmt.Sprintf("[%4d]", t.value)
 			} else {