tidyups and exporting ZPositioner

engine/interface.go

@@ -127,3 +127,11 @@ type Transformer interface {
 type Updater interface {
 	Update() error
 }
+
+// ZPositioner components opt into a simpler method of determining draw order
+// than DrawAfter/DrawBefore. Drawer implementations should handle the
+// ZPositioner case as though the component were a flat infinite plane given by
+// z = ZPos().
+type ZPositioner interface {
+	ZPos() int
+}

engine/misc.go

@@ -40,33 +40,30 @@ func (h *Hidden) Hide() { *h = true }
 // Show sets h to false.
 func (h *Hidden) Show() { *h = false }
 
-// ZPosition implements DrawAfter and DrawPosition as a simple Z coordinate.
+// ZPosition implements DrawAfter and DrawBefore using only Z information.
 type ZPosition int
 
 // DrawAfter reports if z >= x.Max.Z.
 func (z ZPosition) DrawAfter(x Drawer) bool {
-	switch d := x.(type) {
+	switch x := x.(type) {
 	case BoundingBoxer:
-		return int(z) >= d.BoundingBox().Max.Z
+		return int(z) >= x.BoundingBox().Max.Z
-	case zpositioner:
+	case ZPositioner:
-		return z.zposition() > d.zposition()
+		return z.ZPos() > x.ZPos()
 	}
 	return false
 }
 
 // DrawBefore reports if z < x.Min.Z.
 func (z ZPosition) DrawBefore(x Drawer) bool {
-	switch d := x.(type) {
+	switch x := x.(type) {
 	case BoundingBoxer:
-		return int(z) < d.BoundingBox().Min.Z
+		return int(z) < x.BoundingBox().Min.Z
-	case zpositioner:
+	case ZPositioner:
-		return z.zposition() < d.zposition()
+		return z.ZPos() < x.ZPos()
 	}
 	return false
 }
 
-func (z ZPosition) zposition() int { return int(z) }
+// ZPos returns itself.
-
+func (z ZPosition) ZPos() int { return int(z) }
-type zpositioner interface {
-	zposition() int
-}

engine/prisms.go

@@ -148,15 +148,15 @@ func (p *Prism) Draw(screen *ebiten.Image, opts *ebiten.DrawImageOptions) {
 // DrawAfter reports if the prism should be drawn after x.
 func (p *Prism) DrawAfter(x Drawer) bool {
 	pb := p.BoundingBox()
-	switch d := x.(type) {
+	switch x := x.(type) {
 	case *Prism:
 		// Fast path for other prisms
-		if p.pos.Z == d.pos.Z {
+		if p.pos.Z == x.pos.Z {
-			return p.pos.Y < d.pos.Y
+			return p.pos.Y < x.pos.Y
 		}
-		return p.pos.Z > d.pos.Z
+		return p.pos.Z > x.pos.Z
 	case BoundingBoxer:
-		xb := d.BoundingBox()
+		xb := x.BoundingBox()
 		if pb.Max.Z <= xb.Min.Z { // p is behind x
 			return false
 		}
@@ -183,8 +183,8 @@ func (p *Prism) DrawAfter(x Drawer) bool {
 			return true
 		}
 
-	case zpositioner:
+	case ZPositioner:
-		return pb.Min.Z > int(d.zposition()) // p is after x
+		return pb.Min.Z > int(x.ZPos()) // p is after x
 	}
 	return false
 }
@@ -192,15 +192,15 @@ func (p *Prism) DrawAfter(x Drawer) bool {
 // DrawBefore reports if the prism should be drawn before x.
 func (p *Prism) DrawBefore(x Drawer) bool {
 	pb := p.BoundingBox()
-	switch d := x.(type) {
+	switch x := x.(type) {
 	case *Prism:
 		// Fast path for other prisms
-		if p.pos.Z == d.pos.Z {
+		if p.pos.Z == x.pos.Z {
-			return p.pos.Y > d.pos.Y
+			return p.pos.Y > x.pos.Y
 		}
-		return p.pos.Z < d.pos.Z
+		return p.pos.Z < x.pos.Z
 	case BoundingBoxer:
-		xb := d.BoundingBox()
+		xb := x.BoundingBox()
 		if pb.Min.Z >= xb.Max.Z { // p is in front of x
 			return false
 		}
@@ -225,8 +225,8 @@ 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:
+	case ZPositioner:
-		return pb.Max.Z < int(d.zposition()) // p is before x
+		return pb.Max.Z < int(x.ZPos()) // p is before x
 	}
 	return false
 }

engine/sprite.go

@@ -42,9 +42,9 @@ 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 {
 	sb := s.BoundingBox()
-	switch d := x.(type) {
+	switch x := x.(type) {
 	case BoundingBoxer:
-		xb := d.BoundingBox()
+		xb := x.BoundingBox()
 		if sb.Max.Z <= xb.Min.Z { // s is behind x
 			return false
 		}
@@ -57,8 +57,8 @@ func (s *Sprite) DrawAfter(x Drawer) bool {
 		if sb.Max.Y <= xb.Min.Y { // s is above x
 			return true
 		}
-	case zpositioner:
+	case ZPositioner:
-		return sb.Min.Z > int(d.zposition()) // s is after
+		return sb.Min.Z > int(x.ZPos()) // s is after
 	}
 	return false
 }
@@ -66,9 +66,9 @@ func (s *Sprite) DrawAfter(x Drawer) bool {
 // DrawBefore reports if the sprite should be drawn before x.
 func (s *Sprite) DrawBefore(x Drawer) bool {
 	sb := s.BoundingBox()
-	switch d := x.(type) {
+	switch x := x.(type) {
 	case BoundingBoxer:
-		xb := d.BoundingBox()
+		xb := x.BoundingBox()
 		if sb.Min.Z >= xb.Max.Z { // s is in front of x
 			return false
 		}
@@ -81,8 +81,8 @@ func (s *Sprite) DrawBefore(x Drawer) bool {
 		if sb.Min.Y >= xb.Max.Y { // s is below x
 			return true
 		}
-	case zpositioner:
+	case ZPositioner:
-		return sb.Max.Z < int(d.zposition()) // s is before
+		return sb.Max.Z < int(x.ZPos()) // s is before
 	}
 	return false
 }