WIP: refactoring into Less

engine/drawlist.go

@@ -17,12 +17,49 @@ type drawList struct {
 }
 
 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
 	}
+
+	// Common logic for known interfaces (BoundingBoxer, ZPositioner), to
+	// simplify Draw{Before,After} implementations.
+	switch x := d.list[i].(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
+		}
+
+	case ZPositioner:
+		switch y := d.list[j].(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])
 }
 

engine/prisms.go

@@ -158,6 +158,7 @@ func (p *Prism) DrawAfter(x Drawer) bool {
 
 	case BoundingBoxer:
 		xb := x.BoundingBox()
+		if false {
 			if pb.Max.Z <= xb.Min.Z { // p is behind x
 				return false
 			}
@@ -170,6 +171,7 @@ func (p *Prism) DrawAfter(x Drawer) bool {
 			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
@@ -183,8 +185,8 @@ func (p *Prism) DrawAfter(x Drawer) bool {
 			return true
 		}
 
-	case ZPositioner:
+		//case ZPositioner:
-		return pb.Min.Z > int(x.ZPos()) // p is after x
+		//	return pb.Min.Z > x.ZPos() // p is after x
 	}
 	return false
 }
@@ -202,6 +204,7 @@ func (p *Prism) DrawBefore(x Drawer) bool {
 
 	case BoundingBoxer:
 		xb := x.BoundingBox()
+		if false {
 			if pb.Min.Z >= xb.Max.Z { // p is in front of x
 				return false
 			}
@@ -214,6 +217,7 @@ func (p *Prism) DrawBefore(x Drawer) bool {
 			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
@@ -227,8 +231,8 @@ func (p *Prism) DrawBefore(x Drawer) bool {
 			return true
 		}
 
-	case ZPositioner:
+		//case ZPositioner:
-		return pb.Max.Z < int(x.ZPos()) // p is before x
+		//	return pb.Max.Z < x.ZPos() // p is before x
 	}
 	return false
 }

engine/sprite.go

@@ -41,6 +41,7 @@ func (s *Sprite) Draw(screen *ebiten.Image, opts *ebiten.DrawImageOptions) {
 
 // DrawAfter reports if the sprite should be drawn after x.
 func (s *Sprite) DrawAfter(x Drawer) bool {
+	if false {
 		sb := s.BoundingBox()
 		switch x := x.(type) {
 		case BoundingBoxer:
@@ -58,13 +59,15 @@ func (s *Sprite) DrawAfter(x Drawer) bool {
 				return true
 			}
 		case ZPositioner:
-		return sb.Min.Z > int(x.ZPos()) // s is after
+			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 false {
 		sb := s.BoundingBox()
 		switch x := x.(type) {
 		case BoundingBoxer:
@@ -82,7 +85,8 @@ func (s *Sprite) DrawBefore(x Drawer) bool {
 				return true
 			}
 		case ZPositioner:
-		return sb.Max.Z < int(x.ZPos()) // s is before
+			return sb.Max.Z < x.ZPos() // s is before
+		}
 	}
 	return false
 }