WIP: opts -> transform

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() (opts ebiten.DrawImageOptions) {
-	opts.GeoM.Translate(cfloat(b.Pos))
-	return opts
+func (b *Billboard) Transform() (tf Transform) {
+	tf.Opts.GeoM.Translate(cfloat(b.Pos))
+	return tf
 }

engine/camera.go

@@ -3,8 +3,6 @@ package engine
 import (
 	"encoding/gob"
 	"image"
-
-	"github.com/hajimehoshi/ebiten/v2"
 )
 
 // Ensure Camera satisfies interfaces.
@@ -30,6 +28,7 @@ type Camera struct {
 	Centre        image.Point // world coordinates
 	Rotation      float64     // radians
 	Zoom          float64     // unitless
+	IsoProjection image.Point
 
 	game *Game
 }
@@ -86,10 +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() (opts ebiten.DrawImageOptions) {
-	opts.GeoM.Translate(cfloat(c.Centre.Mul(-1)))
-	opts.GeoM.Scale(c.Zoom, c.Zoom)
-	opts.GeoM.Rotate(c.Rotation)
-	opts.GeoM.Translate(cfloat(c.game.ScreenSize.Div(2)))
-	return opts
+func (c *Camera) 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
 }

engine/game.go

@@ -61,7 +61,7 @@ func (g *Game) Draw(screen *ebiten.Image) {
 	// accum memoises the results for each component.
 	type state struct {
 		hidden    bool
-		opts   ebiten.DrawImageOptions
+		transform Transform
 	}
 	accum := map[interface{}]state{
 		g: {hidden: false},
@@ -97,7 +97,7 @@ func (g *Game) Draw(screen *ebiten.Image) {
 			}
 			// p is not hidden, so compute its cumulative transform.
 			if t, ok := p.(Transformer); ok {
-				st.opts = concatOpts(t.Transform(), st.opts)
+				st.transform = t.Transform().Concat(st.transform)
 			}
 			accum[p] = st
 		}
@@ -106,7 +106,7 @@ func (g *Game) Draw(screen *ebiten.Image) {
 		if st.hidden {
 			continue
 		}
-		d.Draw(screen, &st.opts)
+		d.Draw(screen, &st.transform.Opts)
 	}
 }
 
@@ -439,15 +439,3 @@ func (d drawList) Less(i, j int) bool {
 
 func (d drawList) Len() int      { return len(d) }
 func (d drawList) Swap(i, j int) { d[i], d[j] = d[j], d[i] }
-
-func concatOpts(a, b ebiten.DrawImageOptions) ebiten.DrawImageOptions {
-	a.ColorM.Concat(b.ColorM)
-	a.GeoM.Concat(b.GeoM)
-	if b.CompositeMode != 0 {
-		a.CompositeMode = b.CompositeMode
-	}
-	if b.Filter != 0 {
-		a.Filter = b.Filter
-	}
-	return a
-}

engine/interface.go

@@ -107,7 +107,7 @@ type Saver interface {
 
 // Transformer components can transform their child components.
 type Transformer interface {
-	Transform() ebiten.DrawImageOptions
+	Transform() Transform
 }
 
 // Updater components can update themselves. Update is called repeatedly. Each

engine/iso.go

@@ -11,12 +11,12 @@ var (
 	_ interface {
 		Prepper
 		Scanner
+		Transformer
 	} = &IsoVoxmap{}
 
 	_ interface {
 		Prepper
 		Scanner
-		Transformer
 	} = &IsoVoxel{}
 
 	_ Drawer = &IsoVoxelSide{}
@@ -36,7 +36,6 @@ type IsoVoxmap struct {
 	Map           map[Point3]*IsoVoxel
 	DrawOrderBias image.Point // so boxes overdraw correctly
 	DrawOffset    image.Point
-	Projection    image.Point // IsoProjection parameter
 	Sheet         Sheet
 	VoxSize       Point3 // size of each voxel
 }
@@ -61,6 +60,12 @@ func (m *IsoVoxmap) Scan() []interface{} {
 	return c
 }
 
+// Transform returns a translation by DrawOffset.
+func (m *IsoVoxmap) Transform() (tf Transform) {
+	tf.Opts.GeoM.Translate(cfloat(m.DrawOffset))
+	return tf
+}
+
 // IsoVoxel is a voxel in an IsoVoxmap.
 type IsoVoxel struct {
 	CellBack  int // cell to draw for back side
@@ -85,16 +90,6 @@ func (v *IsoVoxel) Scan() []interface{} {
 	return []interface{}{&v.back, &v.front}
 }
 
-// Transform returns a translation of first by DrawOffset, then by
-// pos.CMul(VoxSize) iso-projected (the top-left of the back of the voxel).
-func (v *IsoVoxel) Transform() (opts ebiten.DrawImageOptions) {
-	opts.GeoM.Translate(cfloat(v.ivm.DrawOffset))
-	p3 := v.pos.CMul(v.ivm.VoxSize)
-	p2 := p3.IsoProject(v.ivm.Projection)
-	opts.GeoM.Translate(cfloat(p2))
-	return opts
-}
-
 // IsoVoxelSide is a side of a voxel.
 type IsoVoxelSide struct {
 	front bool
@@ -103,6 +98,12 @@ type IsoVoxelSide struct {
 
 // Draw draws this side.
 func (v *IsoVoxelSide) Draw(screen *ebiten.Image, opts *ebiten.DrawImageOptions) {
+
+	// TODO: apply IsoProjection to opts.GeoM
+	//	p3 := v.pos.CMul(v.ivm.VoxSize)
+	//	p2 := p3.IsoProject(v.ivm.Projection)
+	//	tf.Opts.GeoM.Translate(cfloat(p2))
+
 	cell := v.vox.CellBack
 	if v.front {
 		cell = v.vox.CellFront

engine/parallax.go

@@ -3,8 +3,6 @@ package engine
 import (
 	"encoding/gob"
 	"fmt"
-
-	"github.com/hajimehoshi/ebiten/v2"
 )
 
 var _ interface {
@@ -41,8 +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() (opts ebiten.DrawImageOptions) {
+func (p *Parallax) Transform() (tf Transform) {
 	x, y := cfloat(p.camera.Centre)
-	opts.GeoM.Translate(x*p.Factor, y*p.Factor)
-	return opts
+	tf.Opts.GeoM.Translate(x*p.Factor, y*p.Factor)
+	return tf
 }

engine/sprite.go

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

engine/tiles.go

@@ -109,9 +109,10 @@ func (t *Tilemap) Scan() []interface{} {
 	return c
 }
 
-func (t *Tilemap) Transform() (opts ebiten.DrawImageOptions) {
-	opts.GeoM.Translate(cfloat(t.Offset))
-	return opts
+// Transform returns a translation by t.Offset.
+func (t *Tilemap) Transform() (tf Transform) {
+	tf.Opts.GeoM.Translate(cfloat(t.Offset))
+	return tf
 }
 
 // TileAt returns the tile present at the given world coordinate.

engine/transform.go

@@ -0,0 +1,36 @@
+package engine
+
+import (
+	"image"
+
+	"github.com/hajimehoshi/ebiten/v2"
+)
+
+// Transform is a bucket of things that affect drawing.
+type Transform struct {
+	// IsoProjection is used by isometric 3D components to project their
+	// coordinates into 2D. There's usually only one component in the tree that
+	// sets this field, but it would apply to all descendants.
+	IsoProjection image.Point
+
+	// Opts contains the 2D geometry matrix, the colour matrix, filter mode, and
+	// composition mode.
+	Opts ebiten.DrawImageOptions
+}
+
+// Concat returns the combined transform (a transform equivalent to applying t
+// and then u).
+func (t Transform) Concat(u Transform) Transform {
+	if u.IsoProjection != (image.Point{}) {
+		t.IsoProjection = u.IsoProjection
+	}
+	t.Opts.ColorM.Concat(u.Opts.ColorM)
+	t.Opts.GeoM.Concat(u.Opts.GeoM)
+	if u.Opts.CompositeMode != 0 {
+		t.Opts.CompositeMode = u.Opts.CompositeMode
+	}
+	if u.Opts.Filter != 0 {
+		t.Opts.Filter = u.Opts.Filter
+	}
+	return t
+}

engine/walls.go

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

main.go

@@ -57,6 +57,8 @@ func main() {
 				&engine.Camera{
 					ID:    "game_camera",
 					Child: lev1,
+					// Each step in Z becomes -½ step in X plus ½ step in Y:
+					IsoProjection: image.Pt(-2, 2),
 				},
 				&engine.DebugToast{ID: "toast", Pos: image.Pt(0, 15)},
 				engine.PerfDisplay{},
@@ -129,7 +131,6 @@ func level1() *engine.Scene {
 				ID:            "voxmap",
 				DrawOrderBias: image.Pt(1, -1), // left before right, bottom before top
 				DrawOffset:    image.Pt(-8, 0),
-				Projection:    image.Pt(-2, 2), // each step in Z becomes -1/2 step in X plus 1/2 step in Y.
 				VoxSize:       engine.Pt3(16, 16, 16),
 				Sheet: engine.Sheet{
 					CellSize: image.Pt(24, 24),