feat: add line clear animation

README.md

@@ -64,7 +64,7 @@ go build tetris.go
 
 ## Roadmap
 
-- [ ] Line clear animations
+- [x] Line clear animations
 - [ ] Hard drop and ghost piece
 - [ ] Level/speed progression and pause
 - [ ] High score persistence

game/grid.go

@@ -1,6 +1,8 @@
 package game
 
 import (
+	"slices"
+
 	"tetris/engine/graphics"
 )
 
@@ -44,6 +46,16 @@ func (g *Grid) ClearFullRows() byte {
 	return completed
 }
 
+func (g *Grid) FullRows() []byte {
+	rows := []byte{}
+	for y := byte(0); y < byte(g.Height()); y++ {
+		if g.IsRowFull(y) {
+			rows = append(rows, y)
+		}
+	}
+	return rows
+}
+
 func (g *Grid) IsRowFull(y byte) bool {
 	for x := range byte(g.Width()) {
 		if g.At(x, y) == BLOCK_EMPTY {
@@ -53,6 +65,17 @@ func (g *Grid) IsRowFull(y byte) bool {
 	return true
 }
 
+func (g *Grid) MoveRowsDown(rows ...byte) {
+	completed := byte(0)
+	for y := int(g.Height() - 1); y >= 0; y-- {
+		if slices.Contains(rows, byte(y)) {
+			completed++
+		} else if completed > 0 {
+			g.MoveRowDown(byte(y), completed)
+		}
+	}
+}
+
 func (g *Grid) MoveRowDown(y, num_rows byte) {
 	w := uint16(g.Width())
 	src := uint16(y) * w

game/line_clear_animation.go

@@ -0,0 +1,57 @@
+package game
+
+// LineClearAnimation clears completed lines cell-by-cell to create
+// a visual wipe effect from the center outward.
+//
+// Once the lines are cleared, the remaining lines are moved down.
+type LineClearAnimation struct {
+	// lines to clear.
+	lines []byte
+	// next index to clear to the left
+	leftIndex int8
+	// next index to clear to the right
+	rightIndex int8
+}
+
+func (lca *LineClearAnimation) Reset() {
+	lca.lines = []byte{}
+}
+
+func (lca LineClearAnimation) NumLines() int {
+	return len(lca.lines)
+}
+
+func (lca *LineClearAnimation) SetLines(rows []byte) {
+	lca.lines = rows
+
+	lca.leftIndex = (GRID_WIDTH - 1) / 2
+	if (GRID_WIDTH-1)%2 != 0 {
+		lca.rightIndex = lca.leftIndex + 1
+	} else {
+		lca.rightIndex = lca.leftIndex
+	}
+}
+
+func (lca *LineClearAnimation) Update(grid *Grid) {
+	if lca.Completed() {
+		return
+	}
+
+	if lca.leftIndex < 0 || lca.rightIndex > GRID_WIDTH {
+		grid.MoveRowsDown(lca.lines...)
+		lca.Reset()
+		return
+	}
+
+	for _, lineIndex := range lca.lines {
+		grid.Set(byte(lca.leftIndex), lineIndex, BLOCK_EMPTY)
+		grid.Set(byte(lca.rightIndex), lineIndex, BLOCK_EMPTY)
+	}
+
+	lca.leftIndex--
+	lca.rightIndex++
+}
+
+func (lca LineClearAnimation) Completed() bool {
+	return lca.NumLines() == 0
+}

game/state/handlers/gameplay.go

@@ -21,16 +21,19 @@ type GamePlay struct {
 	score              game.Score
 	dropTimer          core.IntervalTimer
 	moveTimer          core.IntervalTimer
+	lineClearTimer     core.IntervalTimer
 	grid               game.Grid
 	nextShape          game.Shape
 	shapeQueue         *game.ShapeQueue
 	r                  draw.Renderer
+	lineClearAnimation game.LineClearAnimation
 }
 
 func NewGamePlay() *GamePlay {
 	return &GamePlay{
 		dropTimer:      core.NewIntervalTimer(0.3),
 		moveTimer:      core.NewIntervalTimer(0.1),
+		lineClearTimer: core.NewIntervalTimer(0.05),
 		r: draw.Renderer{
 			Theme: &draw.Theme{
 				FrameBG:        color.RGBA{R: 30, G: 30, B: 46, A: 255},
@@ -50,6 +53,7 @@ func (gp *GamePlay) Enter() {
 	gp.shapeQueue = game.NewShapeQueue()
 	gp.nextShape = gp.shapeQueue.Next()
 	gp.SpawnShape()
+	gp.lineClearAnimation.Reset()
 }
 
 func (GamePlay) Exit() {
@@ -81,6 +85,13 @@ func (gp *GamePlay) Update(fsm state.Transitioner, delta float32) {
 		gp.dropTimer.SetInterval(0.3)
 	}
 
+	if !gp.lineClearAnimation.Completed() {
+		if gp.lineClearTimer.UpdateReset(delta) {
+			gp.lineClearAnimation.Update(&gp.grid)
+		}
+		return
+	}
+
 	if rl.IsKeyPressed(rl.KeyUp) {
 		rotated := gp.shape.RotateCW()
 		if !game.CheckShapeCollision(gp.shape_pos, &rotated, &gp.grid) {
@@ -107,16 +118,17 @@ func (gp *GamePlay) Update(fsm state.Transitioner, delta float32) {
 		// Update position if it does not collide
 		if game.CheckShapeCollision(new_pos, &gp.shape, &gp.grid) {
 			gp.LockShape()
-			num_rows := gp.grid.ClearFullRows()
-			if num_rows > 0 {
-				audio.Play(assets.SFX_ROW_CLEARED)
-				gp.score.Lines(num_rows)
-			}
 			gp.SpawnShape()
-
+			lines := gp.grid.FullRows()
+			if len(lines) > 0 {
+				gp.lineClearAnimation.SetLines(lines)
+				gp.score.Lines(byte(len(lines)))
+				audio.Play(assets.SFX_ROW_CLEARED)
+			} else {
 				if game.CheckShapeCollision(gp.shape_pos, &gp.shape, &gp.grid) {
 					fsm.Switch("gameover")
 				}
+			}
 		} else {
 			gp.shape_pos = new_pos
 		}