projection.go, delete crap

engine/box.go

@@ -38,21 +38,21 @@ func (b Box) Size() Point3 {
 
 // Back returns an image.Rectangle representing the back of the box, using
 // the given projection π.
-func (b Box) Back(π image.Point) image.Rectangle {
+func (b Box) Back(π IntProjection) image.Rectangle {
 	b.Max.Z = b.Min.Z
 	return image.Rectangle{
-		Min: b.Min.IsoProject(π),
-		Max: b.Max.IsoProject(π),
+		Min: π.Project(b.Min),
+		Max: π.Project(b.Max),
 	}
 }
 
 // Front returns an image.Rectangle representing the front of the box, using
 // the given projection π.
-func (b Box) Front(π image.Point) image.Rectangle {
+func (b Box) Front(π IntProjection) image.Rectangle {
 	b.Min.Z = b.Max.Z
 	return image.Rectangle{
-		Min: b.Min.IsoProject(π),
-		Max: b.Max.IsoProject(π),
+		Min: π.Project(b.Min),
+		Max: π.Project(b.Max),
 	}
 }
 

engine/camera.go

@@ -28,7 +28,7 @@ type Camera struct {
 	Centre     image.Point // world coordinates
 	Rotation   float64     // radians
 	Zoom       float64     // unitless
-	IsoProjection image.Point
+	Projection IntProjection
 
 	game *Game
 }
@@ -39,7 +39,7 @@ func (c *Camera) PointAt(centre Point3, zoom float64) {
 	// Special sauce: if Child has a BoundingRect, make some adjustments
 	bnd, ok := c.Child.(Bounder)
 	if !ok {
-		c.Centre = centre.IsoProject(c.IsoProjection)
+		c.Centre = c.Projection.Project(centre)
 		c.Zoom = zoom
 		return
 	}
@@ -61,7 +61,7 @@ func (c *Camera) PointAt(centre Point3, zoom float64) {
 	// Camera frame currently Rectangle{ centre ± (screen/(2*zoom)) }.
 	sw2, sh2 := cfloat(c.game.ScreenSize.Div(2))
 	swz, shz := int(sw2/zoom), int(sh2/zoom)
-	cent := centre.IsoProject(c.IsoProjection)
+	cent := c.Projection.Project(centre)
 	if cent.X-swz < br.Min.X {
 		cent.X = br.Min.X + swz
 	}
@@ -88,7 +88,7 @@ func (c *Camera) Scan() []interface{} { return []interface{}{c.Child} }
 
 // Transform returns the camera transform.
 func (c *Camera) Transform(pt Transform) (tf Transform) {
-	tf.IsoProjection = c.IsoProjection
+	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)

engine/projection.go

@@ -1,24 +1,29 @@
 package engine
 
-var (
-	// Oblique projections
-	CabinetProjection  = ParallelProjection{0.5, 0.5}
-	CavalierProjection = ParallelProjection{1, 1}
+import "image"
 
-	// Axonometric projections
-	ElevationProjection = ParallelProjection{0, 0}
-	DimetricProjection  = ParallelProjection{0, 0.5}
-	HexPrismProjection  = ParallelProjection{0, 0.577350269189626} // 1 ÷ √3
-	IsometricProjection = ParallelProjection{0, 0.707106781186548} // 1 ÷ √2
-	TrimetricProjection = ParallelProjection{0, 1}
-)
+type IntProjection image.Point
 
-type ParallelProjection struct {
-	ZX, ZY float64
-}
-
-func (π ParallelProjection) Project(p Point3) (px, py float64) {
-	px = float64(p.X) + π.ZX*float64(p.Z)
-	py = float64(p.Y) + π.ZY*float64(p.Z)
-	return px, py
+// 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 Point3) image.Point {
+	/*
+		I'm using the π character because I'm a maths wanker.
+
+		Dividing is used because there's little reason for an isometric
+		projection in a game to exaggerate the Z position.
+
+		Integers are used to preserve that "pixel perfect" calculation in case
+		you are making the next Celeste.
+	*/
+	q := p.XY()
+	if π.X != 0 {
+		q.X += p.Z / π.X
+	}
+	if π.Y != 0 {
+		q.Y += p.Z / π.Y
+	}
+	return q
 }

engine/sprite.go

@@ -59,7 +59,7 @@ func (s *Sprite) SetAnim(a *Anim) {
 // 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(
-		s.Actor.Pos.IsoProject(pt.IsoProjection).Add(s.DrawOffset),
+		pt.Projection.Project(s.Actor.Pos).Add(s.DrawOffset),
 	))
 	return tf.Concat(pt)
 }

engine/transform.go

@@ -1,17 +1,13 @@
 package engine
 
-import (
-	"image"
-
-	"github.com/hajimehoshi/ebiten/v2"
-)
+import "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
+	// 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.
-	IsoProjection image.Point
+	Projection IntProjection
 
 	// Opts contains the 2D geometry matrix, the colour matrix, filter mode, and
 	// composition mode.
@@ -21,8 +17,8 @@ type Transform struct {
 // 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
+	if u.Projection != (IntProjection{}) {
+		t.Projection = u.Projection
 	}
 	t.Opts.ColorM.Concat(u.Opts.ColorM)
 	t.Opts.GeoM.Concat(u.Opts.GeoM)

main.go

@@ -57,12 +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),
-					// Each step in Z becomes ½ step in Y:
-					//IsoProjection: image.Pt(0, 2),
 					// Each step in Z becomes a step in Y:
-					//IsoProjection: image.Pt(0, 1),
+					Projection: engine.IntProjection{X: 0, Y: 1},
 				},
 				&engine.DebugToast{ID: "toast", Pos: image.Pt(0, 15)},
 				engine.PerfDisplay{},