GeoMDef

engine/misc.go

@@ -1,5 +1,11 @@
 package engine
 
+import (
+	"unsafe"
+
+	"github.com/hajimehoshi/ebiten/v2"
+)
+
 // ID implements Identifier directly (as a string value).
 type ID string
 
@@ -11,3 +17,16 @@ type ZPos float64
 
 // Z returns z as a float64.
 func (z ZPos) Z() float64 { return float64(z) }
+
+// GeoMDef is a serialisable form of GeoM.
+type GeoMDef [6]float64 // Assumption: this has identical memory layout to GeoM
+
+// ToGeoMDef translates a GeoM to a GeoMDef using unsafe.Pointer.
+func ToGeoMDef(m *ebiten.GeoM) *GeoMDef {
+	return (*GeoMDef)(unsafe.Pointer(m))
+}
+
+// GeoM translates a GeoMDef to a GeoM using unsafe.Pointer.
+func (d *GeoMDef) GeoM() *ebiten.GeoM {
+	return (*ebiten.GeoM)(unsafe.Pointer(d))
+}

engine/scene.go

@@ -32,7 +32,7 @@ type Scene struct {
 	Components []interface{}
 	Hidden     bool
 	ID
-	Transform ebiten.GeoM
+	Transform GeoMDef
 	ZPos
 }
 
@@ -41,7 +41,8 @@ func (s *Scene) Draw(screen *ebiten.Image, geom ebiten.GeoM) {
 	if s.Hidden {
 		return
 	}
-	geom.Concat(s.Transform)
+	geom.Concat(*s.Transform.GeoM())
+
 	for _, i := range s.Components {
 		if d, ok := i.(Drawer); ok {
 			d.Draw(screen, geom)

engine/tiles.go

@@ -20,7 +20,7 @@ type Tilemap struct {
 	Map       [][]Tile
 	Src       ImageRef // must be a horizontal tile set
 	TileSize  int
-	Transform ebiten.GeoM
+	Transform GeoMDef
 	ZPos
 }
 
@@ -29,7 +29,7 @@ func (t *Tilemap) Draw(screen *ebiten.Image, geom ebiten.GeoM) {
 	if t.Hidden {
 		return
 	}
-	geom.Concat(t.Transform)
+	geom.Concat(*t.Transform.GeoM())
 	for j, row := range t.Map {
 		for i, tile := range row {
 			var op ebiten.DrawImageOptions