draw the grid explicitly thus leading to full cells w/o the grid

src/play.go

@@ -46,22 +46,22 @@ type ScenePlay struct {
 
 	Clear bool
 
-	Grids         []*Grid       // 2 grids: one current, one next
-	History       History       // holds state of past dead cells for evolution traces
-	Index         int           // points to current grid
-	Generations   int64         // Stats
-	TicksElapsed  int           // tick counter for game speed
-	Camera        Camera        // for zoom+move
-	World, Cache  *ebiten.Image // actual image we render to
-	WheelTurned   bool          // when user turns wheel multiple times, zoom faster
-	Dragging      bool          // middle mouse is pressed, move canvas
-	LastCursorPos []float64     // used to check if the user is dragging
-	MarkTaken     bool          // true when mouse1 pressed
-	MarkDone      bool          // true when mouse1 released, copy cells between Mark+Point
-	Mark, Point   image.Point   // area to marks+save
-	RunOneStep    bool          // mutable flags from config
-	TPG           int           // current game speed (ticks per game)
-	Theme         Theme
+	Grids                   []*Grid       // 2 grids: one current, one next
+	History                 History       // holds state of past dead cells for evolution traces
+	Index                   int           // points to current grid
+	Generations             int64         // Stats
+	TicksElapsed            int           // tick counter for game speed
+	Camera                  Camera        // for zoom+move
+	World, Cache, GridImage *ebiten.Image // actual image we render to
+	WheelTurned             bool          // when user turns wheel multiple times, zoom faster
+	Dragging                bool          // middle mouse is pressed, move canvas
+	LastCursorPos           []float64     // used to check if the user is dragging
+	MarkTaken               bool          // true when mouse1 pressed
+	MarkDone                bool          // true when mouse1 released, copy cells between Mark+Point
+	Mark, Point             image.Point   // area to marks+save
+	RunOneStep              bool          // mutable flags from config
+	TPG                     int           // current game speed (ticks per game)
+	Theme                   Theme
 }
 
 func NewPlayScene(game *Game, config *Config) Scene {
@@ -485,6 +485,13 @@ func (scene *ScenePlay) Draw(screen *ebiten.Image) {
 		}
 	}
 
+	if scene.Config.ShowGrid {
+		// draw the pre-drawn grid onto the world
+		op.GeoM.Reset()
+		op.GeoM.Translate(0, 0)
+		scene.World.DrawImage(scene.GridImage, op)
+	}
+
 	scene.DrawMark(scene.World)
 
 	scene.Camera.Render(scene.World, screen)
@@ -589,6 +596,13 @@ func (scene *ScenePlay) InitCache() {
 	}
 
 	for y := 0; y < scene.Config.Height; y++ {
+		// horizontal grid line
+		vector.StrokeLine(scene.GridImage,
+			float32(0), float32(y*scene.Config.Cellsize),
+			float32(scene.Config.Width*scene.Config.Cellsize), float32(y*scene.Config.Cellsize),
+			1, scene.Theme.Color(ColGrid), false,
+		)
+
 		for x := 0; x < scene.Config.Width; x++ {
 			op.GeoM.Reset()
 			op.GeoM.Translate(
@@ -597,6 +611,13 @@ func (scene *ScenePlay) InitCache() {
 			)
 
 			scene.Cache.DrawImage(scene.Theme.Tile(ColDead), op)
+
+			// vertical grid line
+			vector.StrokeLine(scene.GridImage,
+				float32(x*scene.Config.Cellsize), float32(0),
+				float32(x*scene.Config.Cellsize), float32(scene.Config.Height*scene.Config.Cellsize),
+				1, scene.Theme.Color(ColGrid), false,
+			)
 		}
 	}
 }
@@ -615,6 +636,7 @@ func (scene *ScenePlay) InitGrid() {
 	}
 
 	scene.History = NewHistory(scene.Config.Height, scene.Config.Width)
+
 }
 
 func (scene *ScenePlay) Init() {
@@ -642,10 +664,17 @@ func (scene *ScenePlay) Init() {
 		scene.Config.Height*scene.Config.Cellsize,
 	)
 
+	scene.GridImage = ebiten.NewImage(
+		scene.Config.Width*scene.Config.Cellsize,
+		scene.Config.Height*scene.Config.Cellsize,
+	)
+
 	scene.Theme = scene.Config.ThemeManager.GetCurrentTheme()
 	scene.InitCache()
 
 	if scene.Config.DelayedStart && !scene.Config.Empty {
+		// do not fill the grid when the main menu comes up first, the
+		// user decides interactively what to do
 		scene.Config.Empty = true
 		scene.InitGrid()
 		scene.Config.Empty = false

src/theme.go

@@ -155,8 +155,8 @@ func (manager *ThemeManager) SetCurrentTheme(theme string) {
 func FillCell(tile *ebiten.Image, cellsize int, col color.RGBA) {
 	vector.DrawFilledRect(
 		tile,
-		float32(1),
-		float32(1),
+		float32(0),
+		float32(0),
 		float32(cellsize),
 		float32(cellsize),
 		col, false,