abolish transform

engine/actor.go

@@ -16,13 +16,15 @@ func init() {
 
 // Actor handles basic movement.
 type Actor struct {
-	CollisionDomain  string // id of component to look for colliders inside of
-	Pos, Size        Int3
-	xRem, yRem, zRem float64
+	CollisionDomain string // id of component to look for colliders inside of
+	Pos, Size       Int3   // in voxels; multiply by game.VoxelScale for regular Euclidean space
 
+	rem  Float3
 	game *Game
 }
 
+// CollidesAt runs a collision test of the actor, supposing the actor is at a
+// given position (not necessarily a.Pos).
 func (a *Actor) CollidesAt(p Int3) bool {
 	bounds := Box{Min: p, Max: p.Add(a.Size)}
 	for c := range a.game.Query(a.CollisionDomain, ColliderType) {
@@ -33,13 +35,17 @@ func (a *Actor) CollidesAt(p Int3) bool {
 	return false
 }
 
+// MoveX moves the actor x units in world space. It takes Game.VoxelScale into
+// account (so MoveX(x) moves the actor x/VoxelScale.X voxel units). onCollide
+// is called if a collision occurs, and the actor wil be in the colliding
+// position during the call.
 func (a *Actor) MoveX(x float64, onCollide func()) {
-	a.xRem += x
-	move := int(a.xRem + 0.5) // Note: math.Round can lead to vibration
+	a.rem.X += x / a.game.VoxelScale.X
+	move := int(a.rem.X + 0.5) // Note: math.Round can lead to vibration
 	if move == 0 {
 		return
 	}
-	a.xRem -= float64(move)
+	a.rem.X -= float64(move)
 	sign := sign(move)
 	for move != 0 {
 		a.Pos.X += sign
@@ -51,18 +57,19 @@ func (a *Actor) MoveX(x float64, onCollide func()) {
 			onCollide()
 		}
 		a.Pos.X -= sign
-		a.xRem = 0
+		a.rem.X = 0
 		return
 	}
 }
 
+// MoveY is like MoveX but in the Y dimension. See MoveX for more information.
 func (a *Actor) MoveY(y float64, onCollide func()) {
-	a.yRem += y
-	move := int(a.yRem + 0.5)
+	a.rem.Y += y / a.game.VoxelScale.Y
+	move := int(a.rem.Y + 0.5)
 	if move == 0 {
 		return
 	}
-	a.yRem -= float64(move)
+	a.rem.Y -= float64(move)
 	sign := sign(move)
 	for move != 0 {
 		a.Pos.Y += sign
@@ -74,18 +81,19 @@ func (a *Actor) MoveY(y float64, onCollide func()) {
 			onCollide()
 		}
 		a.Pos.Y -= sign
-		a.yRem = 0
+		a.rem.Y = 0
 		return
 	}
 }
 
+// MoveZ is like MoveX but in the Y dimension. See MoveX for more information.
 func (a *Actor) MoveZ(z float64, onCollide func()) {
-	a.zRem += z
-	move := int(a.zRem + 0.5)
+	a.rem.Z += z / a.game.VoxelScale.Z
+	move := int(a.rem.Z + 0.5)
 	if move == 0 {
 		return
 	}
-	a.zRem -= float64(move)
+	a.rem.Z -= float64(move)
 	sign := sign(move)
 	for move != 0 {
 		a.Pos.Z += sign
@@ -97,11 +105,12 @@ func (a *Actor) MoveZ(z float64, onCollide func()) {
 			onCollide()
 		}
 		a.Pos.Z -= sign
-		a.zRem = 0
+		a.rem.Z = 0
 		return
 	}
 }
 
+// Prepare stores a reference to the game.
 func (a *Actor) Prepare(g *Game) error {
 	a.game = g
 	return nil

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

engine/camera.go

@@ -3,6 +3,8 @@ package engine
 import (
 	"encoding/gob"
 	"image"
+
+	"github.com/hajimehoshi/ebiten/v2"
 )
 
 // Ensure Camera satisfies interfaces.
@@ -87,11 +89,10 @@ 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(pt Transform) (tf Transform) {
-	tf.Projection = c.Projection
-	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.Concat(pt)
+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
 }

engine/game.go

@@ -41,6 +41,7 @@ type Game struct {
 	Hidden
 	ScreenSize image.Point
 	Root       interface{} // typically a *Scene or SceneRef though
+	Projection IntProjection
 	VoxelScale Float3
 
 	dbmu     sync.RWMutex
@@ -61,8 +62,8 @@ func (g *Game) Draw(screen *ebiten.Image) {
 	// parents as well.
 	// accum memoises the results for each component.
 	type state struct {
-		hidden    bool
-		transform Transform
+		hidden bool
+		opts   ebiten.DrawImageOptions
 	}
 	accum := map[interface{}]state{
 		g: {hidden: false},
@@ -96,9 +97,9 @@ func (g *Game) Draw(screen *ebiten.Image) {
 				accum[p] = state{hidden: true}
 				continue
 			}
-			// p is not hidden, so compute its cumulative transform.
+			// p is not hidden, so compute its cumulative opts.
 			if tf, ok := p.(Transformer); ok {
-				st.transform = tf.Transform(st.transform)
+				st.opts = ConcatOpts(tf.Transform(), st.opts)
 			}
 			accum[p] = st
 		}
@@ -107,7 +108,7 @@ func (g *Game) Draw(screen *ebiten.Image) {
 		if st.hidden {
 			continue
 		}
-		d.Draw(screen, &st.transform.Opts)
+		d.Draw(screen, &st.opts)
 	}
 }
 
@@ -265,6 +266,10 @@ func postorderWalk(component, parent interface{}, visit func(component, parent i
 // builds the component databases and then calls Prepare on every Preparer.
 // LoadAndPrepare must be called before any calls to Component or Query.
 func (g *Game) LoadAndPrepare(assets fs.FS) error {
+	if g.VoxelScale == (Float3{}) {
+		g.VoxelScale = Float3{1, 1, 1}
+	}
+
 	// Load all the Loaders.
 	startLoad := time.Now()
 	if err := PreorderWalk(g, func(c, _ interface{}) error {
@@ -440,3 +445,17 @@ 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] }
+
+// ConcatOpts returns the combined options (as though a was applied and then
+// b).
+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

@@ -105,17 +105,11 @@ type Saver interface {
 	Save() error
 }
 
-// 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)
-// 	}
+// Transformer components can provide draw options to apply to themselves and
+// any child components. The opts passed to Draw of a component c will be the
+// cumulative opts of all parents of c plus the value returned from c.Transform.
 type Transformer interface {
-	Transform(Transform) Transform
+	Transform() ebiten.DrawImageOptions
 }
 
 // Updater components can update themselves. Update is called repeatedly. Each

engine/parallax.go

@@ -3,6 +3,8 @@ package engine
 import (
 	"encoding/gob"
 	"fmt"
+
+	"github.com/hajimehoshi/ebiten/v2"
 )
 
 var _ interface {
@@ -39,8 +41,8 @@ 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(pt Transform) (tf Transform) {
+func (p *Parallax) Transform() (opts ebiten.DrawImageOptions) {
 	x, y := cfloat(p.camera.Centre)
-	tf.Opts.GeoM.Translate(x*p.Factor, y*p.Factor)
-	return tf.Concat(pt)
+	opts.GeoM.Translate(x*p.Factor, y*p.Factor)
+	return opts
 }

engine/prisms.go

@@ -57,9 +57,9 @@ func (m *PrismMap) Prepare(*Game) error {
 	return nil
 }
 
-func (m *PrismMap) Transform(pt Transform) (tf Transform) {
-	tf.Opts.GeoM.Translate(cfloat(m.DrawOffset))
-	return tf.Concat(pt)
+func (m *PrismMap) Transform() (opts ebiten.DrawImageOptions) {
+	opts.GeoM.Translate(cfloat(m.DrawOffset))
+	return opts
 }
 
 type Prism struct {
@@ -78,9 +78,9 @@ func (p *Prism) DrawOrder() (int, int) {
 		dot(p.pos.XY(), p.pm.DrawOrderBias)
 }
 
-func (p *Prism) Transform(pt Transform) (tf Transform) {
-	tf.Opts.GeoM.Translate(cfloat(
+func (p *Prism) Transform() (opts ebiten.DrawImageOptions) {
+	opts.GeoM.Translate(cfloat(
 		p.pm.PosToDraw.Apply(p.pos),
 	))
-	return tf.Concat(pt)
+	return opts
 }

engine/projection.go

@@ -2,10 +2,12 @@ package engine
 
 import "image"
 
+// IntProjection holds an integer projection definition.
+// It is designed for projecting Z onto X and Y with integer fractions as would
+// be used in e.g. a diametric projection (IntProjection{X:0, Y:-2}).
 type IntProjection image.Point
 
 // Project performs an integer parallel projection of a 3D coordinate into 2D.
-//
 // If π.X = 0, the x returned is p.X; similarly for π.Y and y.
 // Otherwise, x projects to x + z/π.X and y projects to y + z/π.Y.
 func (π IntProjection) Project(p Int3) image.Point {

engine/sprite.go

@@ -56,12 +56,15 @@ func (s *Sprite) SetAnim(a *Anim) {
 	s.anim = a
 }
 
-// Transform returns a translation by the DrawOffset and the iso-projected Pos.
-func (s *Sprite) Transform(pt Transform) (tf Transform) {
-	tf.Opts.GeoM.Translate(cfloat(
-		pt.Projection.Project(s.Actor.Pos).Add(s.DrawOffset),
+// Transform returns a translation by the DrawOffset and Actor.Pos projected
+func (s *Sprite) Transform() (opts ebiten.DrawImageOptions) {
+	opts.GeoM.Translate(cfloat(
+		// Reaching into Actor for a reference to Game so I don't have to
+		// implement Prepare in this file, but writing this long comment
+		// providing exposition...
+		s.Actor.game.Projection.Project(s.Actor.Pos).Add(s.DrawOffset),
 	))
-	return tf.Concat(pt)
+	return opts
 }
 
 // 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(pt Transform) (tf Transform) {
-	tf.Opts.GeoM.Translate(cfloat(t.Offset))
-	return tf.Concat(pt)
+func (t *Tilemap) Transform() (opts ebiten.DrawImageOptions) {
+	opts.GeoM.Translate(cfloat(t.Offset))
+	return opts
 }
 
 // TileAt returns the tile present at the given world coordinate.

engine/transform.go

@@ -1,32 +0,0 @@
-package engine
-
-import "github.com/hajimehoshi/ebiten/v2"
-
-// Transform is a bucket of things that affect drawing.
-type Transform struct {
-	// Projection 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.
-	Projection IntProjection
-
-	// 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.Projection != (IntProjection{}) {
-		t.Projection = u.Projection
-	}
-	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(pt Transform) (tf Transform) {
-	tf.Opts.GeoM.Translate(cfloat(w.Offset))
-	return tf.Concat(pt)
+func (w *Wall) Transform() (opts ebiten.DrawImageOptions) {
+	opts.GeoM.Translate(cfloat(w.Offset))
+	return opts
 }
 
 // WallUnit is a unit in a wall. Unlike a tile in a tilemap, WallUnit is
@@ -105,9 +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(pt Transform) (tf Transform) {
-	tf.Opts.GeoM.Translate(cfloat(
+func (u *WallUnit) Transform() (opts ebiten.DrawImageOptions) {
+	opts.GeoM.Translate(cfloat(
 		cmul(u.pos, u.wall.UnitSize).Add(u.wall.UnitOffset),
 	))
-	return tf.Concat(pt)
+	return opts
 }

main.go

@@ -5,6 +5,7 @@ import (
 	"image/color"
 	_ "image/png"
 	"log"
+	"math"
 	"os"
 	"runtime"
 	"runtime/pprof"
@@ -51,6 +52,13 @@ func main() {
 
 	g := &engine.Game{
 		ScreenSize: image.Pt(320, 240),
+		Projection: engine.IntProjection{X: 0, Y: 1},
+		VoxelScale: engine.Float3{
+			// Each voxel counts for this much Eucliden space:
+			X: 1,
+			Y: 1,
+			Z: math.Sqrt(3),
+		},
 		Root: &engine.Scene{
 			ID: "root",
 			Components: []interface{}{