From a680cca30c24feb9f0a53911232d987f760eef3e Mon Sep 17 00:00:00 2001
From: Thomas von Dein <tom@vondein.org>
Date: Tue, 16 Jul 2024 19:33:06 +0200
Subject: [PATCH] always calculate neighbor count

---
 src/grid.go | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
 src/play.go |  2 +-
 2 files changed, 63 insertions(+), 2 deletions(-)

diff --git a/src/grid.go b/src/grid.go
index 1000bf8..b1e6098 100644
--- a/src/grid.go
+++ b/src/grid.go
@@ -25,6 +25,7 @@ type Grid struct {
 	Neighbors     [][]Neighbor
 	Empty         bool
 	Config        *Config
+	Counter       func(x, y int) uint8
 }
 
 // Create new empty grid and allocate Data according to provided dimensions
@@ -58,6 +59,12 @@ func NewGrid(config *Config) *Grid {
 		}
 	}
 
+	if grid.Config.Wrap {
+		grid.Counter = grid.CountNeighborsWrap
+	} else {
+		grid.Counter = grid.CountNeighbors
+	}
+
 	return grid
 }
 
@@ -101,8 +108,62 @@ func (grid *Grid) SetupNeighbors(x, y int) {
 	grid.Neighbors[y+STRIDE*x] = neighbors
 }
 
-// count the living neighbors of a cell
+func (grid *Grid) CountNeighborsWrap(x, y int) uint8 {
+	var sum uint8
+
+	for nbgX := -1; nbgX < 2; nbgX++ {
+		for nbgY := -1; nbgY < 2; nbgY++ {
+			var col, row int
+
+			// In wrap mode we look at all the 8 neighbors surrounding us.
+			// In case we are on an edge we'll look at the neighbor on the
+			//  other side  of the  grid, thus  wrapping lookahead  around
+			// using the mod() function.
+			col = (x + nbgX + grid.Config.Width) % grid.Config.Width
+			row = (y + nbgY + grid.Config.Height) % grid.Config.Height
+
+			sum += grid.Data[row+STRIDE*col]
+		}
+	}
+
+	// don't count ourselfes though
+	sum -= grid.Data[y+STRIDE*x]
+
+	return sum
+}
+
 func (grid *Grid) CountNeighbors(x, y int) uint8 {
+	var sum uint8
+
+	width := grid.Config.Width
+	height := grid.Config.Height
+
+	for nbgX := -1; nbgX < 2; nbgX++ {
+		for nbgY := -1; nbgY < 2; nbgY++ {
+			var col, row int
+
+			xnbgX := x + nbgX
+			ynbgY := y + nbgY
+
+			// In traditional grid mode the edges are deadly
+			if xnbgX < 0 || xnbgX >= width || ynbgY < 0 || ynbgY >= height {
+				continue
+			}
+			col = xnbgX
+			row = ynbgY
+
+			sum += grid.Data[row+STRIDE*col]
+		}
+	}
+
+	// don't count ourselfes though
+	sum -= grid.Data[y+STRIDE*x]
+
+	return sum
+}
+
+// count the living neighbors of a cell
+func (grid *Grid) _CountNeighbors(x, y int) uint8 {
 	var count uint8
 
 	pos := y + STRIDE*x
diff --git a/src/play.go b/src/play.go
index 2a8f3a1..d5d8d8e 100644
--- a/src/play.go
+++ b/src/play.go
@@ -167,7 +167,7 @@ func (scene *ScenePlay) UpdateCells() {
 
 			for x := 0; x < width; x++ {
 				state := scene.Grids[scene.Index].Data[y+STRIDE*x] // 0|1 == dead or alive
-				neighbors := scene.Grids[scene.Index].CountNeighbors(x, y)
+				neighbors := scene.Grids[scene.Index].Counter(x, y)
 
 				// actually apply the current rules
 				nextstate := scene.RuleCheckFunc(state, neighbors)