remove sort method

engine/drawlist.go

@@ -8,8 +8,6 @@ import (
 	"github.com/hajimehoshi/ebiten/v2"
 )
 
-const commonDrawerComparisons = true
-
 var _ Drawer = tombstone{}
 
 type tombstone struct{}
@@ -26,63 +24,55 @@ type drawList struct {
 	rev  map[Drawer]int
 }
 
-func (d drawList) Less(i, j int) bool {
-	// Deal with tombstones first, in case anything else thinks it
-	// needs to go last.
-	if d.list[i] == (tombstone{}) {
-		return false
-	}
-	if d.list[j] == (tombstone{}) {
-		return true
-	}
-
-	if commonDrawerComparisons {
-		// Common logic for known interfaces (BoundingBoxer, ZPositioner), to
-		// simplify Draw{Before,After} implementations.
-		switch x := d.list[i].(type) {
+// edge reports if there is a draw ordering constraint between u and v (where
+// u draws before v).
+func edge(u, v Drawer) bool {
+	// Common logic for known interfaces (BoundingBoxer, ZPositioner), to
+	// simplify DrawOrderer implementations.
+	switch x := u.(type) {
+	case BoundingBoxer:
+		xb := x.BoundingBox()
+		switch y := v.(type) {
 		case BoundingBoxer:
-			xb := x.BoundingBox()
-			switch y := d.list[j].(type) {
-			case BoundingBoxer:
-				yb := y.BoundingBox()
-				if xb.Min.Z >= yb.Max.Z { // x is in front of y
-					return false
-				}
-				if xb.Max.Z <= yb.Min.Z { // x is behind y
-					return true
-				}
-				if xb.Max.Y <= yb.Min.Y { // x is above y
-					return false
-				}
-				if xb.Min.Y >= yb.Max.Y { // x is below y
-					return true
-				}
-			case ZPositioner:
-				return xb.Max.Z < y.ZPos() // x is before y
+			yb := y.BoundingBox()
+			if xb.Min.Z >= yb.Max.Z { // x is in front of y
+				return false
+			}
+			if xb.Max.Z <= yb.Min.Z { // x is behind y
+				return true
+			}
+			if xb.Max.Y <= yb.Min.Y { // x is above y
+				return false
+			}
+			if xb.Min.Y >= yb.Max.Y { // x is below y
+				return true
 			}
-
 		case ZPositioner:
-			switch y := d.list[j].(type) {
-			case BoundingBoxer:
-				return x.ZPos() < y.BoundingBox().Min.Z
-			case ZPositioner:
-				return x.ZPos() < y.ZPos()
-			}
+			return xb.Max.Z < y.ZPos() // x is before y
+		}
+
+	case ZPositioner:
+		switch y := v.(type) {
+		case BoundingBoxer:
+			return x.ZPos() < y.BoundingBox().Min.Z
+		case ZPositioner:
+			return x.ZPos() < y.ZPos()
 		}
 	}
 
-	// Fallback case: ask the components themselves
-	return d.list[i].DrawBefore(d.list[j]) || d.list[j].DrawAfter(d.list[i])
+	// Fallback case: ask the components themselves if they have an opinion
+	if do, ok := u.(DrawOrderer); ok && do.DrawBefore(v) {
+		return true
+	}
+	if do, ok := v.(DrawOrderer); ok && do.DrawAfter(u) {
+		return true
+	}
+
+	// No relation
+	return false
 }
 
-func (d drawList) Len() int { return len(d.list) }
-
-func (d drawList) Swap(i, j int) {
-	d.rev[d.list[i]], d.rev[d.list[j]] = j, i
-	d.list[i], d.list[j] = d.list[j], d.list[i]
-}
-
-// Slow topological sort. Uses a projection π to flatten bounding boxes for
+// Topological sort. Uses a projection π to flatten bounding boxes for
 // overlap tests, in order to reduce edge count.
 func (d *drawList) topsort(π geom.Projector) {
 	// Produce edge lists and count indegrees - O(|V|^2)
@@ -113,7 +103,7 @@ func (d *drawList) topsort(π geom.Projector) {
 			}
 
 			// If the edge goes u->v, add it.
-			if d.Less(i, j) {
+			if edge(u, v) {
 				edges[i] = append(edges[i], j)
 				indegree[j]++
 			}

engine/game.go

@@ -8,7 +8,6 @@ import (
 	"io/fs"
 	"log"
 	"reflect"
-	"sort"
 	"sync"
 	"time"
 
@@ -17,7 +16,7 @@ import (
 	"github.com/hajimehoshi/ebiten/v2/ebitenutil"
 )
 
-const topologicalDrawSort = true
+const showDrawListSize = true
 
 var _ interface {
 	Disabler
@@ -114,7 +113,7 @@ func (g *Game) Draw(screen *ebiten.Image) {
 		d.Draw(screen, &st.opts)
 	}
 
-	if true {
+	if showDrawListSize {
 		// Infodump about draw list
 		ebitenutil.DebugPrintAt(screen, fmt.Sprintf("len(drawList.list) = %d", len(g.drawList.list)), 0, 30)
 		ebitenutil.DebugPrintAt(screen, fmt.Sprintf("len(drawList.rev) = %d", len(g.drawList.list)), 0, 45)
@@ -185,19 +184,7 @@ func (g *Game) Update() error {
 	}
 
 	// Sort the draw list (on every frame - this isn't as bad as it sounds)
-	if topologicalDrawSort {
-		g.drawList.topsort(g.Projection)
-	} else {
-		sort.Stable(g.drawList)
-
-		// Truncate tombstones from the end.
-		for i := g.drawList.Len() - 1; i >= 0; i-- {
-			if g.drawList.list[i] != (tombstone{}) {
-				break
-			}
-			g.drawList.list = g.drawList.list[:i]
-		}
-	}
+	g.drawList.topsort(g.Projection)
 	return nil
 }
 

engine/interface.go

@@ -72,6 +72,11 @@ type Disabler interface {
 // passed to Game.Register or returned from Scan).
 type Drawer interface {
 	Draw(*ebiten.Image, *ebiten.DrawImageOptions)
+}
+
+// DrawOrderer components have more specific ideas about draw ordering than
+// merely "my Z is bigger than yours".
+type DrawOrderer interface {
 	DrawAfter(Drawer) bool
 	DrawBefore(Drawer) bool
 }

engine/misc.go

@@ -40,30 +40,8 @@ func (h *Hides) Hide() { *h = true }
 // Show sets h to false.
 func (h *Hides) Show() { *h = false }
 
-// ZPosition implements DrawAfter and DrawBefore using only Z information.
+// ZPosition implements ZPositioner directly (as an int).
 type ZPosition int
 
-// DrawAfter reports if z >= x.Max.Z.
-func (z ZPosition) DrawAfter(x Drawer) bool {
-	switch x := x.(type) {
-	case BoundingBoxer:
-		return int(z) >= x.BoundingBox().Max.Z
-	case ZPositioner:
-		return z.ZPos() > x.ZPos()
-	}
-	return false
-}
-
-// DrawBefore reports if z < x.Min.Z.
-func (z ZPosition) DrawBefore(x Drawer) bool {
-	switch x := x.(type) {
-	case BoundingBoxer:
-		return int(z) < x.BoundingBox().Min.Z
-	case ZPositioner:
-		return z.ZPos() < x.ZPos()
-	}
-	return false
-}
-
 // ZPos returns itself.
 func (z ZPosition) ZPos() int { return int(z) }

engine/prisms.go

@@ -158,20 +158,6 @@ func (p *Prism) DrawAfter(x Drawer) bool {
 
 	case BoundingBoxer:
 		xb := x.BoundingBox()
-		if !commonDrawerComparisons {
-			if pb.Max.Z <= xb.Min.Z { // p is behind x
-				return false
-			}
-			if pb.Min.Z >= xb.Max.Z { // p is in front of x
-				return true
-			}
-			if pb.Min.Y >= xb.Max.Y { // p is below x
-				return false
-			}
-			if pb.Max.Y <= xb.Min.Y { // p is above x
-				return true
-			}
-		}
 		// The prism special
 		split := p.m.topext[geom.North].X
 		threshold := p.m.topext[geom.East].Y
@@ -184,9 +170,6 @@ func (p *Prism) DrawAfter(x Drawer) bool {
 		if pb.Min.Z+threshold >= xb.Max.Z { // x is behind the front half of p
 			return true
 		}
-
-	case ZPositioner:
-		return pb.Min.Z > x.ZPos() // p is after x
 	}
 	return false
 }
@@ -204,20 +187,6 @@ func (p *Prism) DrawBefore(x Drawer) bool {
 
 	case BoundingBoxer:
 		xb := x.BoundingBox()
-		if !commonDrawerComparisons {
-			if pb.Min.Z >= xb.Max.Z { // p is in front of x
-				return false
-			}
-			if pb.Max.Z <= xb.Min.Z { // p is behind x
-				return true
-			}
-			if pb.Max.Y <= xb.Min.Y { // p is above x
-				return false
-			}
-			if pb.Min.Y >= xb.Max.Y { // p is below x
-				return true
-			}
-		}
 		// The prism special
 		split := p.m.topext[geom.North].X
 		threshold := p.m.topext[geom.East].Y
@@ -230,9 +199,6 @@ func (p *Prism) DrawBefore(x Drawer) bool {
 		if pb.Min.Z+threshold <= xb.Min.Z { // x is in front of the front half of p
 			return true
 		}
-
-	case ZPositioner:
-		return pb.Max.Z < x.ZPos() // p is before x
 	}
 	return false
 }

engine/sprite.go

@@ -40,58 +40,6 @@ func (s *Sprite) Draw(screen *ebiten.Image, opts *ebiten.DrawImageOptions) {
 	screen.DrawImage(s.Sheet.SubImage(s.anim.Cell()), opts)
 }
 
-// DrawAfter reports if the sprite should be drawn after x.
-func (s *Sprite) DrawAfter(x Drawer) bool {
-	if !commonDrawerComparisons {
-		sb := s.BoundingBox()
-		switch x := x.(type) {
-		case BoundingBoxer:
-			xb := x.BoundingBox()
-			if sb.Max.Z <= xb.Min.Z { // s is behind x
-				return false
-			}
-			if sb.Min.Z >= xb.Max.Z { // s is in front of x
-				return true
-			}
-			if sb.Min.Y >= xb.Max.Y { // s is below x
-				return false
-			}
-			if sb.Max.Y <= xb.Min.Y { // s is above x
-				return true
-			}
-		case ZPositioner:
-			return sb.Min.Z > x.ZPos() // s is after
-		}
-	}
-	return false
-}
-
-// DrawBefore reports if the sprite should be drawn before x.
-func (s *Sprite) DrawBefore(x Drawer) bool {
-	if !commonDrawerComparisons {
-		sb := s.BoundingBox()
-		switch x := x.(type) {
-		case BoundingBoxer:
-			xb := x.BoundingBox()
-			if sb.Min.Z >= xb.Max.Z { // s is in front of x
-				return false
-			}
-			if sb.Max.Z <= xb.Min.Z { // s is behind x
-				return true
-			}
-			if sb.Max.Y <= xb.Min.Y { // s is above x
-				return false
-			}
-			if sb.Min.Y >= xb.Max.Y { // s is below x
-				return true
-			}
-		case ZPositioner:
-			return sb.Max.Z < x.ZPos() // s is before
-		}
-	}
-	return false
-}
-
 // Scan returns the Actor and the Sheet.
 func (s *Sprite) Scan() []interface{} {
 	return []interface{}{

game/aw.go

@@ -11,6 +11,8 @@ import (
 	"github.com/hajimehoshi/ebiten/v2/inpututil"
 )
 
+const awakemanProducesBubbles = true
+
 var _ interface {
 	engine.Identifier
 	engine.Disabler
@@ -109,7 +111,7 @@ func (aw *Awakeman) realUpdate() error {
 		bubblePeriod   = 6
 	)
 
-	if true {
+	if awakemanProducesBubbles {
 		// Add a bubble?
 		aw.bubbleTimer--
 		if aw.bubbleTimer <= 0 {