Transform now responsible for concat

engine/billboard.go

@@ -36,7 +36,7 @@ func (b *Billboard) Draw(screen *ebiten.Image, opts *ebiten.DrawImageOptions) {
 // Scan returns a slice containing Src.
 func (b *Billboard) Scan() []interface{} { return []interface{}{&b.Src} }
 
-func (b *Billboard) Transform() (tf Transform) {
+func (b *Billboard) Transform(pt Transform) (tf Transform) {
 	tf.Opts.GeoM.Translate(cfloat(b.Pos))
-	return tf
+	return tf.Concat(pt)
 }

engine/camera.go

@@ -85,11 +85,11 @@ func (c *Camera) Prepare(game *Game) error {
 func (c *Camera) Scan() []interface{} { return []interface{}{c.Child} }
 
 // Transform returns the camera transform.
-func (c *Camera) Transform() (tf Transform) {
+func (c *Camera) Transform(pt Transform) (tf Transform) {
 	tf.IsoProjection = c.IsoProjection
 	tf.Opts.GeoM.Translate(cfloat(c.Centre.Mul(-1)))
 	tf.Opts.GeoM.Scale(c.Zoom, c.Zoom)
 	tf.Opts.GeoM.Rotate(c.Rotation)
 	tf.Opts.GeoM.Translate(cfloat(c.game.ScreenSize.Div(2)))
-	return tf
+	return tf.Concat(pt)
 }

engine/game.go

@@ -96,8 +96,8 @@ func (g *Game) Draw(screen *ebiten.Image) {
 				continue
 			}
 			// p is not hidden, so compute its cumulative transform.
-			if t, ok := p.(Transformer); ok {
-				st.transform = t.Transform().Concat(st.transform)
+			if tf, ok := p.(Transformer); ok {
+				st.transform = tf.Transform(st.transform)
 			}
 			accum[p] = st
 		}

engine/interface.go

@@ -105,9 +105,17 @@ type Saver interface {
 	Save() error
 }
 
-// Transformer components can transform their child components.
+// Transformer components can provide a transform to apply to themselves and any
+// child components, based on the cumulative parent transform. An
+// example implementation:
+//
+// 	func (f Foo) Transform(pt Transform) Transform {
+// 		var tf Transform
+// 		tf.Opts.GeoM.Translate(-2, 3) // or your own transform
+// 		return tf.Concat(pt)
+// 	}
 type Transformer interface {
-	Transform() Transform
+	Transform(Transform) Transform
 }
 
 // Updater components can update themselves. Update is called repeatedly. Each

engine/iso.go

@@ -17,6 +17,7 @@ var (
 	_ interface {
 		Prepper
 		Scanner
+		Transformer
 	} = &IsoVoxel{}
 
 	_ Drawer = &IsoVoxelSide{}
@@ -61,9 +62,9 @@ func (m *IsoVoxmap) Scan() []interface{} {
 }
 
 // Transform returns a translation by DrawOffset.
-func (m *IsoVoxmap) Transform() (tf Transform) {
+func (m *IsoVoxmap) Transform(pt Transform) (tf Transform) {
 	tf.Opts.GeoM.Translate(cfloat(m.DrawOffset))
-	return tf
+	return tf.Concat(pt)
 }
 
 // IsoVoxel is a voxel in an IsoVoxmap.
@@ -90,6 +91,14 @@ func (v *IsoVoxel) Scan() []interface{} {
 	return []interface{}{&v.back, &v.front}
 }
 
+// Transform returns a translation the isoprojected coordinate of this voxel.
+func (v *IsoVoxel) Transform(pt Transform) (tf Transform) {
+	tf.Opts.GeoM.Translate(cfloat(
+		v.pos.CMul(v.ivm.VoxSize).IsoProject(pt.IsoProjection),
+	))
+	return tf.Concat(pt)
+}
+
 // IsoVoxelSide is a side of a voxel.
 type IsoVoxelSide struct {
 	front bool

engine/parallax.go

@@ -39,8 +39,8 @@ func (p *Parallax) Prepare(game *Game) error {
 func (p *Parallax) Scan() []interface{} { return []interface{}{p.Child} }
 
 // Transform returns a GeoM translation of Factor * camera.Centre.
-func (p *Parallax) Transform() (tf Transform) {
+func (p *Parallax) Transform(pt Transform) (tf Transform) {
 	x, y := cfloat(p.camera.Centre)
 	tf.Opts.GeoM.Translate(x*p.Factor, y*p.Factor)
-	return tf
+	return tf.Concat(pt)
 }

engine/sprite.go

@@ -57,9 +57,9 @@ func (s *Sprite) SetAnim(a *Anim) {
 }
 
 // Transform returns a translation by the FrameOffset.
-func (s *Sprite) Transform() (tf Transform) {
+func (s *Sprite) Transform(pt Transform) (tf Transform) {
 	tf.Opts.GeoM.Translate(cfloat(s.Actor.Pos.XY().Add(s.FrameOffset)))
-	return tf
+	return tf.Concat(pt)
 }
 
 // Update updates the Sprite's anim. anim can change a bit so we don't tell Game

engine/tiles.go

@@ -110,9 +110,9 @@ func (t *Tilemap) Scan() []interface{} {
 }
 
 // Transform returns a translation by t.Offset.
-func (t *Tilemap) Transform() (tf Transform) {
+func (t *Tilemap) Transform(pt Transform) (tf Transform) {
 	tf.Opts.GeoM.Translate(cfloat(t.Offset))
-	return tf
+	return tf.Concat(pt)
 }
 
 // TileAt returns the tile present at the given world coordinate.

engine/walls.go

@@ -80,9 +80,9 @@ func (w *Wall) Prepare(*Game) error {
 }
 
 // Transform returns a GeoM translation by Offset.
-func (w *Wall) Transform() (tf Transform) {
+func (w *Wall) Transform(pt Transform) (tf Transform) {
 	tf.Opts.GeoM.Translate(cfloat(w.Offset))
-	return tf
+	return tf.Concat(pt)
 }
 
 // WallUnit is a unit in a wall. Unlike a tile in a tilemap, WallUnit is
@@ -105,7 +105,9 @@ func (u *WallUnit) Draw(screen *ebiten.Image, opts *ebiten.DrawImageOptions) {
 // Scan returns the Tile.
 func (u *WallUnit) Scan() []interface{} { return []interface{}{u.Tile} }
 
-func (u *WallUnit) Transform() (tf Transform) {
-	tf.Opts.GeoM.Translate(cfloat(cmul(u.pos, u.wall.UnitSize).Add(u.wall.UnitOffset)))
-	return tf
+func (u *WallUnit) Transform(pt Transform) (tf Transform) {
+	tf.Opts.GeoM.Translate(cfloat(
+		cmul(u.pos, u.wall.UnitSize).Add(u.wall.UnitOffset),
+	))
+	return tf.Concat(pt)
 }