fix: join terrain columns if possible

If two columns with same x position "touch" themselves and there is no hole between them they can be joined to one.

Joining of columns should reduce entities count.

terrain/column.go

@@ -70,3 +70,9 @@ func (t *Column) BottomLine() (int, int) {
 func (t *Column) MakeHole(cx, cy, r int) {
 	t.terrain.MakeHole(cx, cy, r)
 }
+
+// SetCanvas changes canvas of this column
+func (t *Column) SetCanvas(canvas *tl.Canvas) {
+	t.canvas = canvas
+	t.Entity.SetCanvas(canvas)
+}

terrain/cutter.go

@@ -67,7 +67,7 @@ func (c *Cutter) Draw(s *tl.Screen) {
 	// process all pending cuts
 	for _, cut := range c.cuts {
 
-		// for each x which is should be cut we will create new columns updated by current cut
+		// for each x which should be cut we will create new columns updated by current cut
 		newcols := []*Column{}
 		for _, column := range c.terrain.columns[cut.X] {
 

terrain/joiner.go

@@ -0,0 +1,67 @@
+package terrain
+
+import (
+	tl "github.com/JoelOtter/termloop"
+	"github.com/zladovan/gorched/debug"
+)
+
+// Joiner is responsible for joining terrain columns.
+// If two columns with same x position "touch" themselves and there is no hole between them they can be joined to one.
+// Joiner is by default not enabled. You need to activate it by calling Enable. Then it will be enabled for 1 second.
+type Joiner struct {
+	// terrain is reference to the terrain which columns will be joined
+	terrain *Terrain
+	// ttl is number of seconds till joiner will be not active
+	ttl float64
+
+}
+
+// Draw will perform joining logic if this joiner is enabled
+func (j *Joiner) Draw(s *tl.Screen) {
+	// early exit if not enabled
+	if j.ttl <= 0 {
+		return
+	}
+	j.ttl -= s.TimeDelta()
+
+	for x, columns := range j.terrain.columns {
+		// nothing to join
+		if len(columns) <= 1 {
+			continue
+		}
+
+		joined := []*Column{columns[0]}
+		for _, column := range columns[1:] {
+			last := joined[len(joined)-1]
+			_, ly := last.Position()
+			_, lh := last.Size()
+			_, y := column.Position()
+
+			// no need to join
+			if ly + lh < y {
+				joined = append(joined, column)
+				continue
+			}
+
+			// joining
+			// canvas of last column is added to the canvas of current colum
+			debug.Logf("Joining terrain columns x=%d y1=%d y2=%d", x, ly, lh)
+			column.SetCanvas(&tl.Canvas{append((*last.canvas)[0], (*column.canvas)[0]...)})
+
+			// replace and remove last column
+			joined[len(joined) - 1] = column
+			s.Level().RemoveEntity(last)
+		}
+
+		// replace original columns with joined
+		j.terrain.columns[x] = joined
+	}
+}
+
+// Tick does nothing now
+func (j *Joiner) Tick(e tl.Event) {}
+
+// Enable this joiner for one second
+func (j *Joiner) Enable() {
+	j.ttl = 1
+}

terrain/terrain.go

@@ -21,6 +21,8 @@ type Terrain struct {
 	columns [][]*Column
 	// cutter provides terrain destruction logic
 	cutter *Cutter
+	// joiner provides terrain columns joining logic
+	joiner *Joiner
 }
 
 // NewTerrain creates new Terrain for given terrain line and height.
@@ -30,6 +32,7 @@ func NewTerrain(line []int, height int, lowColor bool) *Terrain {
 	terrain := &Terrain{height: height}
 	terrain.columns = make([][]*Column, len(line))
 	terrain.cutter = &Cutter{terrain: terrain}
+	terrain.joiner = &Joiner{terrain: terrain}
 
 	// create column for each point in terrain line
 	for x, baseY := range line {
@@ -75,7 +78,7 @@ func (t *Terrain) PositionOn(x int) gmath.Vector2i {
 
 // Entities returns all entities (columns) which is terrain made of
 func (t *Terrain) Entities() []tl.Drawable {
-	entities := []tl.Drawable{t.cutter}
+	entities := []tl.Drawable{t.cutter, t.joiner}
 	for _, cs := range t.columns {
 		for _, c := range cs {
 			entities = append(entities, c)
@@ -101,6 +104,7 @@ func (t *Terrain) CutAround(x, y, w int) {
 func (t *Terrain) MakeHole(cx, cy, r int) {
 	debug.Logf("Hole in the terrain centerx=%d, centery=%d", cx, cy)
 	t.cutter.CutHole(cx, cy, r)
+	t.joiner.Enable()
 }
 
 // Line returns terrain line array where index is x coordinate and value is top y coordinate.