From 27cbaf9403b53e0f80315d0a044ff13e87da1693 Mon Sep 17 00:00:00 2001
From: Josh Deprez <DrJosh9000@users.noreply.github.com>
Date: Mon, 2 Aug 2021 15:16:58 +1000
Subject: [PATCH] actor

---
 engine/actor.go | 66 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100644 engine/actor.go

diff --git a/engine/actor.go b/engine/actor.go
new file mode 100644
index 0000000..e52e9bc
--- /dev/null
+++ b/engine/actor.go
@@ -0,0 +1,66 @@
+package engine
+
+import "math"
+
+// Thorson-style movement:
+// https://maddythorson.medium.com/celeste-and-towerfall-physics-d24bd2ae0fc5
+
+const collide = false // TODO: add collision detection
+
+type Actor struct {
+	X, Y int
+
+	game       *Game
+	xRem, yRem float64
+}
+
+func (a *Actor) MoveX(dx float64, onCollide func()) {
+	a.xRem += dx
+	move := int(math.Round(a.xRem))
+	if move == 0 {
+		return
+	}
+	a.xRem -= float64(move)
+	sign := sign(move)
+	for move != 0 {
+		if collide {
+			if onCollide != nil {
+				onCollide()
+			}
+			return
+		}
+		a.X += sign
+		move -= sign
+	}
+}
+
+func (a *Actor) MoveY(dy float64, onCollide func()) {
+	a.yRem += dy
+	move := int(math.Round(a.yRem))
+	if move == 0 {
+		return
+	}
+	a.yRem -= float64(move)
+	sign := sign(move)
+	for move != 0 {
+		if collide {
+			if onCollide != nil {
+				onCollide()
+			}
+			return
+		}
+		a.Y += sign
+		move -= sign
+	}
+}
+
+func (a *Actor) Build(g *Game) {
+	a.game = g
+}
+
+func sign(m int) int {
+	if m < 0 {
+		return -1
+	}
+	return 1
+}