collision detection woo

engine/actor.go

@@ -1,19 +1,46 @@
 package engine
 
-import "math"
+import (
+	"encoding/gob"
+	"image"
+	"math"
+)
+
+func init() {
+	gob.Register(Actor{})
+}
 
 // Thorson-style movement:
 // https://maddythorson.medium.com/celeste-and-towerfall-physics-d24bd2ae0fc5
 
-const collide = false // TODO: add collision detection
+// Collider components have tangible form.
+type Collider interface {
+	CollidesWith(image.Rectangle) bool
+}
 
 type Actor struct {
-	X, Y int
+	Position image.Point
+	Size     image.Point
 
 	game       *Game
 	xRem, yRem float64
 }
 
+func (a *Actor) collidesAt(p image.Point) bool {
+	// TODO: more efficient test?
+	hit := false
+	a.game.Walk(func(c interface{}) bool {
+		if coll, ok := c.(Collider); ok {
+			if coll.CollidesWith(image.Rectangle{Min: p, Max: p.Add(a.Size)}) {
+				hit = true
+				return false
+			}
+		}
+		return true
+	})
+	return hit
+}
+
 func (a *Actor) MoveX(dx float64, onCollide func()) {
 	a.xRem += dx
 	move := int(math.Round(a.xRem))
@@ -23,13 +50,13 @@ func (a *Actor) MoveX(dx float64, onCollide func()) {
 	a.xRem -= float64(move)
 	sign := sign(move)
 	for move != 0 {
-		if collide {
+		if a.collidesAt(a.Position.Add(image.Pt(sign, 0))) {
 			if onCollide != nil {
 				onCollide()
 			}
 			return
 		}
-		a.X += sign
+		a.Position.X += sign
 		move -= sign
 	}
 }
@@ -43,13 +70,13 @@ func (a *Actor) MoveY(dy float64, onCollide func()) {
 	a.yRem -= float64(move)
 	sign := sign(move)
 	for move != 0 {
-		if collide {
+		if a.collidesAt(a.Position.Add(image.Pt(0, sign))) {
 			if onCollide != nil {
 				onCollide()
 			}
 			return
 		}
-		a.Y += sign
+		a.Position.Y += sign
 		move -= sign
 	}
 }

engine/solid.go

@@ -0,0 +1,16 @@
+package engine
+
+import (
+	"encoding/gob"
+	"image"
+)
+
+func init() {
+	gob.Register(SolidRect{})
+}
+
+type SolidRect struct {
+	Rect image.Rectangle
+}
+
+func (s SolidRect) CollidesWith(r image.Rectangle) bool { return s.Rect.Overlaps(r) }