Overhaul the Platformer Physics System

* Player character now experiences acceleration and friction when
  walking around the map!
* Actor position and movement had to be converted from int's
  (render.Point) to float64's to support fine-grained acceleration
  steps.
* Added "physics" package and physics.Vector to be a float64 counterpart
  for render.Point. Vector is used for uix.Actor.Position() for the sake
  of movement math. Vector is flattened back to a render.Point for
  collision purposes, since the levels and hitboxes are pixel-bound.
* Refactor the uix.Actor to no longer extend the doodads.Drawing (so it
  can have a Position that's a Vector instead of a Point). This broke
  some code that expected `.Doodad` to directly reference the
  Drawing.Doodad: now you had to refer to it as `a.Drawing.Doodad` which
  was ugly. Added convenience method .Doodad() for a shortcut.
* Moved functions like GetBoundingRect() from doodads package to
  collision, where it uses its own slimmer Actor interface for just the
  relevant methods it needs.

dev-assets/doodads/azulian/azulian-red.js

@@ -1,5 +1,5 @@
 function main() {
-	log.Info("Azulian '%s' initialized!", Self.Doodad.Title);
+	log.Info("Azulian '%s' initialized!", Self.Doodad().Title);
 
 	var playerSpeed = 4;
 	var gravity = 4;
@@ -28,8 +28,10 @@ function main() {
 		}
 		sampleTick++;
 
-		var Vx = playerSpeed * (direction === "left" ? -1 : 1);
-		Self.SetVelocity(Point(Vx, 0));
+		// TODO: Vector() requires floats, pain in the butt for JS,
+		// the JS API should be friendlier and custom...
+		var Vx = parseFloat(playerSpeed * (direction === "left" ? -1 : 1));
+		Self.SetVelocity(Vector(Vx, 0.0));
 
 		if (!Self.IsAnimating()) {
 			Self.PlayAnimation("walk-"+direction, null);

dev-assets/doodads/buttons/button.js

@@ -1,5 +1,5 @@
 function main() {
-	console.log("%s initialized!", Self.Doodad.Title);
+	console.log("%s initialized!", Self.Doodad().Title);
 
 	var timer = 0;
 
@@ -28,7 +28,7 @@ function main() {
 	});
 
 	// Events.OnLeave(function(e) {
-	// 	console.log("%s has stopped touching %s", e, Self.Doodad.Title)
+	// 	console.log("%s has stopped touching %s", e, Self.Doodad().Title)
 	// 	Self.Canvas.SetBackground(RGBA(0, 0, 1, 0));
 	// })
 }

dev-assets/doodads/buttons/sticky.js

@@ -1,5 +1,5 @@
 function main() {
-	console.log("%s initialized!", Self.Doodad.Title);
+	console.log("%s initialized!", Self.Doodad().Title);
 
 	var pressed = false;
 

dev-assets/doodads/doors/colored-door.js

@@ -1,6 +1,6 @@
 
 function main() {
-	var color = Self.Doodad.Tag("color");
+	var color = Self.Doodad().Tag("color");
 	var keyname = "key-" + color + ".doodad";
 
 	// Layers in the doodad image.

dev-assets/doodads/doors/electric-door.js

@@ -1,5 +1,5 @@
 function main() {
-	console.log("%s initialized!", Self.Doodad.Title);
+	console.log("%s initialized!", Self.Doodad().Title);
 
 	Self.AddAnimation("open", 100, [0, 1, 2, 3]);
 	Self.AddAnimation("close", 100, [3, 2, 1, 0]);
@@ -9,7 +9,7 @@ function main() {
 	Self.SetHitbox(16, 0, 32, 64);
 
 	Message.Subscribe("power", function(powered) {
-		console.log("%s got power=%+v", Self.Doodad.Title, powered);
+		console.log("%s got power=%+v", Self.Doodad().Title, powered);
 
 		if (powered) {
 			if (animating || opened) {

dev-assets/doodads/doors/keys.js

@@ -1,9 +1,9 @@
 function main() {
-	var color = Self.Doodad.Tag("color");
+	var color = Self.Doodad().Tag("color");
 
 	Events.OnCollide(function(e) {
 		if (e.Settled) {
-			e.Actor.AddItem(Self.Doodad.Filename, 0);
+			e.Actor.AddItem(Self.Doodad().Filename, 0);
 			Self.Destroy();
 		}
 	})

dev-assets/doodads/doors/locked-door.js

@@ -2,7 +2,7 @@
 function main() {
 	Self.AddAnimation("open", 0, [1]);
 	var unlocked = false;
-	var color = Self.Doodad.Tag("color");
+	var color = Self.Doodad().Tag("color");
 
 	Self.SetHitbox(16, 0, 32, 64);
 

dev-assets/doodads/mischievous.js

@@ -1,5 +1,5 @@
 function main() {
-	console.log("%s initialized!", Self.Doodad.Title);
+	console.log("%s initialized!", Self.Doodad().Title);
 
 	console.log(Object.keys(console));
 	console.log(Object.keys(log));

dev-assets/doodads/objects/exit-flag.js

@@ -1,6 +1,6 @@
 // Exit Flag.
 function main() {
-	console.log("%s initialized!", Self.Doodad.Title);
+	console.log("%s initialized!", Self.Doodad().Title);
 	Self.SetHitbox(22+16, 16, 75-16, 86);
 
 	Events.OnCollide(function(e) {

dev-assets/doodads/on-off/state-button.js

@@ -4,7 +4,7 @@
 var state = false;
 
 function main() {
-	console.log("%s ID '%s' initialized!", Self.Doodad.Title, Self.ID());
+	console.log("%s ID '%s' initialized!", Self.Doodad().Title, Self.ID());
 	Self.SetHitbox(0, 0, 33, 33);
 
 	// When the button is activated, don't keep toggling state until we're not

dev-assets/doodads/switches/switch.js

@@ -1,5 +1,5 @@
 function main() {
-	console.log("%s initialized!", Self.Doodad.Title);
+	console.log("%s initialized!", Self.Doodad().Title);
 
 	// Switch has two frames:
 	// 0: Off

dev-assets/doodads/trapdoors/down.js

@@ -1,5 +1,5 @@
 function main() {
-	console.log("%s initialized!", Self.Doodad.Title);
+	console.log("%s initialized!", Self.Doodad().Title);
 
 	var timer = 0;
 

dev-assets/doodads/trapdoors/trapdoor.js

@@ -1,6 +1,6 @@
 function main() {
 	// What direction is the trapdoor facing?
-	var direction = Self.Doodad.Tag("direction");
+	var direction = Self.Doodad().Tag("direction");
 	console.log("Trapdoor(%s) initialized", direction);
 
 	var timer = 0;

dev-assets/guidebook/pages/DoodadScripts.md

@@ -16,7 +16,7 @@ function main() {
     //   other doodads.
 
     // Logs go to the game's log file (standard output on Linux/Mac).
-    console.log("%s initialized!", Self.Doodad.Title);
+    console.log("%s initialized!", Self.Doodad().Title);
 
     // If our doodad has 'solid' parts that should prohibit movement,
     // define the hitbox here. Coordinates are relative so 0,0 is the
@@ -59,13 +59,13 @@ Self holds information about the current doodad. The full surface area of
 the Self object is subject to change, but some useful things you can access
 from it include:
 
-* Self.Doodad: a pointer to the doodad's file data.
-  * Self.Doodad.Title: get the title of the doodad file.
-  * Self.Doodad.Author: the name of the author who wrote the doodad.
-  * Self.Doodad.Script: the doodad's JavaScript source code. Note that
+* Self.Doodad(): a pointer to the doodad's file data.
+  * Self.Doodad().Title: get the title of the doodad file.
+  * Self.Doodad().Author: the name of the author who wrote the doodad.
+  * Self.Doodad().Script: the doodad's JavaScript source code. Note that
     modifying this won't have any effect in-game, as the script had already
     been loaded into the interpreter.
-  * Self.Doodad.GameVersion: the version of {{ app_name }} that was used
+  * Self.Doodad().GameVersion: the version of {{ app_name }} that was used
     when the doodad was created.
 
 ### Events

docs/public/Doodad Scripts.md

@@ -14,7 +14,7 @@ Provide a script file with a `main` function:
 
 ```javascript
 function main() {
-  console.log("%s initialized!", Self.Doodad.Title);
+  console.log("%s initialized!", Self.Doodad().Title);
 
   var timer = 0;
   Events.OnCollide( function() {
@@ -84,18 +84,18 @@ The global variable `Self` holds an API for the current doodad. The full
 surface area of this API is subject to change, but some useful examples you
 can do with this are as follows.
 
-### Self.Doodad
+### Self.Doodad()
 
-Self.Doodad is a pointer into the doodad's metadata file. Not
+Self.Doodad() is a pointer into the doodad's metadata file. Not
 all properties in there can be written to or read from the
 JavaScript engine, but some useful attributes are:
 
-* `str Self.Doodad.Title`: the title of the doodad.
-* `str Self.Doodad.Author`: the author name of the doodad.
-* `str Self.Doodad.Script`: your own source code. Note that
+* `str Self.Doodad().Title`: the title of the doodad.
+* `str Self.Doodad().Author`: the author name of the doodad.
+* `str Self.Doodad().Script`: your own source code. Note that
   editing this won't have any effect in-game, as your doodad's
   source has already been loaded into the interpreter.
-* `str Self.Doodad.GameVersion`: the game version that created
+* `str Self.Doodad().GameVersion`: the game version that created
   the doodad.
 
 ### Self.ShowLayer(int index)

pkg/balance/numbers.go

@@ -14,9 +14,9 @@ var (
 	ScrollboxVert = 128
 
 	// Player speeds
-	PlayerMaxVelocity  = 6
-	PlayerAcceleration = 2
-	Gravity            = 6
+	PlayerMaxVelocity  float64 = 6
+	PlayerAcceleration float64 = 0.2
+	Gravity            float64 = 6
 
 	// Default chunk size for canvases.
 	ChunkSize = 128

pkg/collision/bounding_rect.go

@@ -0,0 +1,42 @@
+package collision
+
+import "git.kirsle.net/go/render"
+
+// GetBoundingRect computes the full pairs of points for the bounding box of
+// the actor.
+//
+// The X,Y coordinates are the position in the level of the actor,
+// The W,H are the size of the actor's drawn box.
+func GetBoundingRect(a Actor) render.Rect {
+	var (
+		P = a.Position()
+		S = a.Size()
+	)
+	return render.Rect{
+		X: P.X,
+		Y: P.Y,
+		W: S.W,
+		H: S.H,
+	}
+}
+
+// GetBoundingRectHitbox returns the bounding rect of the Actor taking into
+// account their self-declared collision hitbox.
+//
+// The rect returned has the X,Y coordinate set to the actor's position, plus
+// the X,Y of their hitbox, if any.
+//
+// The W,H of the rect is the W,H of their declared hitbox.
+//
+// If the actor has NOT declared its hitbox, this function returns exactly the
+// same way as GetBoundingRect() does.
+func GetBoundingRectHitbox(a Actor, hitbox render.Rect) render.Rect {
+	rect := GetBoundingRect(a)
+	if !hitbox.IsZero() {
+		rect.X += hitbox.X
+		rect.Y += hitbox.Y
+		rect.W = hitbox.W
+		rect.H = hitbox.H
+	}
+	return rect
+}

pkg/collision/collide_actors.go

@@ -7,6 +7,15 @@ import (
 	"git.kirsle.net/go/render"
 )
 
+// Actor is a subset of the uix.Actor interface with just the methods needed
+// for collision checking purposes.
+type Actor interface {
+	Position() render.Point
+	Size() render.Rect
+	Grounded() bool
+	SetGrounded(bool)
+}
+
 // BoxCollision holds the result of a collision BetweenBoxes.
 type BoxCollision struct {
 	// A and B are the indexes of the boxes sent to BetweenBoxes.

pkg/collision/collide_level.go

@@ -3,7 +3,6 @@ package collision
 import (
 	"sync"
 
-	"git.kirsle.net/apps/doodle/pkg/doodads"
 	"git.kirsle.net/apps/doodle/pkg/level"
 	"git.kirsle.net/go/render"
 )
@@ -53,7 +52,7 @@ CollidesWithGrid checks if a Doodad collides with level geometry.
 
 The `target` is the point the actor wants to move to on this tick.
 */
-func CollidesWithGrid(d doodads.Actor, grid *level.Chunker, target render.Point) (*Collide, bool) {
+func CollidesWithGrid(d Actor, grid *level.Chunker, target render.Point) (*Collide, bool) {
 	var (
 		P = d.Position()
 		S = d.Size()
@@ -72,7 +71,7 @@ func CollidesWithGrid(d doodads.Actor, grid *level.Chunker, target render.Point)
 	)
 
 	// Test all of the bounding boxes for a collision with level geometry.
-	if ok := result.ScanBoundingBox(doodads.GetBoundingRect(d), grid); ok {
+	if ok := result.ScanBoundingBox(GetBoundingRect(d), grid); ok {
 		// We've already collided! Try to wiggle free.
 		if result.Bottom {
 			if !d.Grounded() {

pkg/doodads/actor.go

@@ -10,8 +10,8 @@ type Actor interface {
 	ID() string
 
 	// Position and velocity, not saved to disk.
-	Position() render.Point
-	Velocity() render.Point
+	Position() render.Point // DEPRECATED
+	Velocity() render.Point // DEPRECATED for uix.Actor
 	Size() render.Rect
 	Grounded() bool
 	SetGrounded(bool)
@@ -24,51 +24,3 @@ type Actor interface {
 	MoveBy(render.Point) // Add {X,Y} to current Position.
 	MoveTo(render.Point) // Set current Position to {X,Y}.
 }
-
-// GetBoundingRect computes the full pairs of points for the bounding box of
-// the actor.
-//
-// The X,Y coordinates are the position in the level of the actor,
-// The W,H are the size of the actor's drawn box.
-func GetBoundingRect(d Actor) render.Rect {
-	var (
-		P = d.Position()
-		S = d.Size()
-	)
-	return render.Rect{
-		X: P.X,
-		Y: P.Y,
-		W: S.W,
-		H: S.H,
-	}
-}
-
-// GetBoundingRectHitbox returns the bounding rect of the Actor taking into
-// account their self-declared collision hitbox.
-//
-// The rect returned has the X,Y coordinate set to the actor's position, plus
-// the X,Y of their hitbox, if any.
-//
-// The W,H of the rect is the W,H of their declared hitbox.
-//
-// If the actor has NOT declared its hitbox, this function returns exactly the
-// same way as GetBoundingRect() does.
-func GetBoundingRectHitbox(d Actor, hitbox render.Rect) render.Rect {
-	rect := GetBoundingRect(d)
-	if !hitbox.IsZero() {
-		rect.X += hitbox.X
-		rect.Y += hitbox.Y
-		rect.W = hitbox.W
-		rect.H = hitbox.H
-	}
-	return rect
-}
-
-// GetBoundingRectWithHitbox is like GetBoundingRect but adjusts it for the
-// relative hitbox of the actor.
-// func GetBoundingRectWithHitbox(d Actor, hitbox render.Rect) render.Rect {
-// 	rect := GetBoundingRect(d)
-// 	rect.W = hitbox.W
-// 	rect.H = hitbox.H
-// 	return rect
-// }

pkg/doodads/drawing.go

@@ -20,11 +20,11 @@ type Drawing struct {
 
 // NewDrawing creates a Drawing actor based on a Doodad drawing. If you pass
 // an empty ID string, it will make a random UUIDv4 ID.
-func NewDrawing(id string, doodad *Doodad) Drawing {
+func NewDrawing(id string, doodad *Doodad) *Drawing {
 	if id == "" {
 		id = uuid.Must(uuid.NewRandom()).String()
 	}
-	return Drawing{
+	return &Drawing{
 		id:     id,
 		Doodad: doodad,
 		size:   doodad.Rect(),

pkg/doodads/dummy/dummy.go

@@ -1,11 +1,14 @@
 // Package dummy implements a dummy doodads.Drawing.
 package dummy
 
-import "git.kirsle.net/apps/doodle/pkg/doodads"
+import (
+	"git.kirsle.net/apps/doodle/pkg/doodads"
+	"git.kirsle.net/go/render"
+)
 
 // Drawing is a dummy doodads.Drawing that has no data.
 type Drawing struct {
-	doodads.Drawing
+	Drawing *doodads.Drawing
 }
 
 // NewDrawing creates a new dummy drawing.
@@ -14,3 +17,8 @@ func NewDrawing(id string, doodad *doodads.Doodad) *Drawing {
 		Drawing: doodads.NewDrawing(id, doodad),
 	}
 }
+
+// Size returns the size of the underlying doodads.Drawing.
+func (d *Drawing) Size() render.Rect {
+	return d.Drawing.Size()
+}

pkg/editor_ui.go

@@ -348,7 +348,7 @@ func (u *EditorUI) SetupCanvas(d *Doodle) *uix.Canvas {
 		b.Actor.AddLink(idA)
 
 		// Reset the Link tool.
-		d.Flash("Linked '%s' and '%s' together", a.Doodad.Title, b.Doodad.Title)
+		d.Flash("Linked '%s' and '%s' together", a.Doodad().Title, b.Doodad().Title)
 	}
 
 	// Set up the drop handler for draggable doodads.

pkg/fps.go

@@ -142,7 +142,7 @@ func (d *Doodle) DrawCollisionBox(actor doodads.Actor) {
 	}
 
 	var (
-		rect = doodads.GetBoundingRect(actor)
+		rect = collision.GetBoundingRect(actor)
 		box  = collision.GetCollisionBox(rect)
 	)
 

pkg/physics/math.go

@@ -0,0 +1,15 @@
+package physics
+
+// Lerp performs linear interpolation between two numbers.
+//
+// a and b are the two bounds of the number, and t is a fraction between 0 and
+// 1 that will return a number between a and b. If t=0, returns a; if t=1,
+// returns b.
+func Lerp(a, b, t float64) float64 {
+	return (1.0-t)*a + t*b
+}
+
+// LerpInt runs lerp using integers.
+func LerpInt(a, b int, t float64) float64 {
+	return Lerp(float64(a), float64(b), t)
+}

pkg/physics/math_test.go

@@ -0,0 +1,38 @@
+package physics_test
+
+import (
+	"testing"
+
+	"git.kirsle.net/apps/doodle/pkg/physics"
+)
+
+func TestLerp(t *testing.T) {
+	var tests = []struct {
+		Inputs []float64
+		Expect float64
+	}{
+		{
+			Inputs: []float64{0, 1, 0.75},
+			Expect: 0.75,
+		},
+		{
+			Inputs: []float64{0, 100, 0.5},
+			Expect: 50.0,
+		},
+		{
+			Inputs: []float64{10, 75, 0.3},
+			Expect: 29.5,
+		},
+		{
+			Inputs: []float64{30, 2, 0.75},
+			Expect: 9,
+		},
+	}
+
+	for _, test := range tests {
+		result := physics.Lerp(test.Inputs[0], test.Inputs[1], test.Inputs[2])
+		if result != test.Expect {
+			t.Errorf("Lerp(%+v) expected %f but got %f", test.Inputs, test.Expect, result)
+		}
+	}
+}

pkg/physics/movement.go

@@ -0,0 +1,33 @@
+package physics
+
+// Mover is a moving object.
+type Mover struct {
+	Acceleration float64
+	Friction     float64
+	// Gravity      Vector
+
+	// // Position and previous frame's position.
+	// Position    render.Point
+	// OldPosition render.Point
+	//
+	// // Speed and previous frame's speed.
+	// Speed    render.Point
+	// OldSpeed render.Point
+	MaxSpeed Vector
+	//
+	// // Object is on the ground and its grounded state last frame.
+	// Grounded    bool
+	// WasGrounded bool
+}
+
+// NewMover initializes state for a moving object.
+func NewMover() *Mover {
+	return &Mover{}
+}
+
+// // UpdatePhysics runs calculations on the mover's physics each frame.
+// func (m *Mover) UpdatePhysics() {
+// 	m.OldPosition = m.Position
+// 	m.OldSpeed = m.Speed
+// 	m.WasGrounded = m.Grounded
+// }

pkg/physics/vector.go

@@ -0,0 +1,54 @@
+package physics
+
+import (
+	"fmt"
+	"math"
+
+	"git.kirsle.net/go/render"
+)
+
+// Vector holds floating point values on an X and Y coordinate.
+type Vector struct {
+	X float64
+	Y float64
+}
+
+// NewVector creates a Vector from X and Y values.
+func NewVector(x, y float64) Vector {
+	return Vector{
+		X: x,
+		Y: y,
+	}
+}
+
+// VectorFromPoint converts a render.Point into a vector.
+func VectorFromPoint(p render.Point) Vector {
+	return Vector{
+		X: float64(p.X),
+		Y: float64(p.Y),
+	}
+}
+
+// IsZero returns if the vector is zero.
+func (v Vector) IsZero() bool {
+	return v.X == 0 && v.Y == 0
+}
+
+// Add to the vector.
+func (v *Vector) Add(other Vector) {
+	v.X += other.X
+	v.Y += other.Y
+}
+
+// ToPoint converts the vector into a render.Point with integer coordinates.
+func (v Vector) ToPoint() render.Point {
+	return render.Point{
+		X: int(math.Round(v.X)),
+		Y: int(math.Round(v.Y)),
+	}
+}
+
+// String encoding of the vector.
+func (v Vector) String() string {
+	return fmt.Sprintf("%f,%f", v.X, v.Y)
+}

pkg/physics/vector_test.go

@@ -0,0 +1,53 @@
+package physics_test
+
+import (
+	"testing"
+
+	"git.kirsle.net/apps/doodle/pkg/physics"
+	"git.kirsle.net/go/render"
+)
+
+// Test converting points to vectors and back again.
+func TestVectorPoint(t *testing.T) {
+	var tests = []struct {
+		In  render.Point
+		Mid physics.Vector
+		Add physics.Vector
+		Out render.Point
+	}{
+		{
+			In:  render.NewPoint(102, 102),
+			Mid: physics.NewVector(102.0, 102.0),
+			Out: render.NewPoint(102, 102),
+		},
+		{
+			In:  render.NewPoint(64, 128),
+			Mid: physics.NewVector(64.0, 128.0),
+			Add: physics.NewVector(0.4, 0.6),
+			Out: render.NewPoint(64, 129),
+		},
+	}
+
+	for _, test := range tests {
+		// Convert point to vector.
+		v := physics.VectorFromPoint(test.In)
+		if v != test.Mid {
+			t.Errorf("Unexpected Vector from Point(%s): wanted %s, got %s",
+				test.In, test.Mid, v,
+			)
+			continue
+		}
+
+		// Add other vector.
+		v.Add(test.Add)
+
+		// Verify output point rounded down correctly.
+		out := v.ToPoint()
+		if out != test.Out {
+			t.Errorf("Unexpected output vector from Point(%s) -> V(%s) + V(%s): wanted %s, got %s",
+				test.In, test.Mid, test.Add, test.Out, out,
+			)
+			continue
+		}
+	}
+}

pkg/play_inventory.go

@@ -39,8 +39,8 @@ func (s *PlayScene) setupInventoryHud() {
 
 	// Add the inventory frame to the screen frame.
 	s.screen.Place(s.invenFrame, ui.Place{
-		Left:   40,
-		Bottom: 40,
+		Top:   40,
+		Right: 40,
 	})
 
 	// Hide inventory if empty.

pkg/play_scene.go

@@ -8,6 +8,7 @@ import (
 	"git.kirsle.net/apps/doodle/pkg/doodads"
 	"git.kirsle.net/apps/doodle/pkg/level"
 	"git.kirsle.net/apps/doodle/pkg/log"
+	"git.kirsle.net/apps/doodle/pkg/physics"
 	"git.kirsle.net/apps/doodle/pkg/scripting"
 	"git.kirsle.net/apps/doodle/pkg/uix"
 	"git.kirsle.net/go/render"
@@ -51,6 +52,7 @@ type PlayScene struct {
 
 	// Player character
 	Player            *uix.Actor
+	playerPhysics     *physics.Mover
 	antigravity       bool // Cheat: disable player gravity
 	noclip            bool // Cheat: disable player clipping
 	playerJumpCounter int  // limit jump length
@@ -235,6 +237,14 @@ func (s *PlayScene) setupPlayer() {
 	s.drawing.AddActor(s.Player)
 	s.drawing.FollowActor = s.Player.ID()
 
+	// Set up the movement physics for the player.
+	s.playerPhysics = &physics.Mover{
+		MaxSpeed: physics.NewVector(balance.PlayerMaxVelocity, balance.PlayerMaxVelocity),
+		// Gravity:      physics.NewVector(balance.Gravity, balance.Gravity),
+		Acceleration: 0.025,
+		Friction:     0.1,
+	}
+
 	// Set up the player character's script in the VM.
 	if err := s.scripting.AddLevelScript(s.Player.ID()); err != nil {
 		log.Error("PlayScene.Setup: scripting.InstallActor(player) failed: %s", err)
@@ -412,7 +422,7 @@ func (s *PlayScene) Draw(d *Doodle) error {
 	s.drawing.Present(d.Engine, s.drawing.Point())
 
 	// Draw out bounding boxes.
-	d.DrawCollisionBox(s.Player)
+	d.DrawCollisionBox(s.Player.Drawing)
 
 	// Draw the UI screen and any widgets that attached to it.
 	s.screen.Compute(d.Engine)
@@ -445,36 +455,80 @@ func (s *PlayScene) Draw(d *Doodle) error {
 
 // movePlayer updates the player's X,Y coordinate based on key pressed.
 func (s *PlayScene) movePlayer(ev *event.State) {
-	var playerSpeed = balance.PlayerMaxVelocity
+	var (
+		playerSpeed = float64(balance.PlayerMaxVelocity)
+		velocity    = s.Player.Velocity()
+		direction   float64
+		jumping     bool
+	)
 
-	// If antigravity enabled and the Shift key is pressed down, move the
-	// player by only one pixel per tick.
-	if s.antigravity && ev.Shift {
+	// Antigravity: player can move anywhere with arrow keys.
+	if s.antigravity {
+		velocity.X = 0
+		velocity.Y = 0
+
+		// Shift to slow your roll to 1 pixel per tick.
+		if ev.Shift {
 			playerSpeed = 1
 		}
 
-	var velocity render.Point
-
 		if ev.Left {
 			velocity.X = -playerSpeed
-	}
-	if ev.Right {
+		} else if ev.Right {
 			velocity.X = playerSpeed
 		}
-	if ev.Up && (s.Player.Grounded() || s.playerJumpCounter >= 0 || s.antigravity) {
+		if ev.Up {
 			velocity.Y = -playerSpeed
-
-		if s.Player.Grounded() {
-			s.playerJumpCounter = 12
-		}
-	}
-	if ev.Down && s.antigravity {
+		} else if ev.Down {
 			velocity.Y = playerSpeed
 		}
+	} else {
+		// Moving left or right.
+		if ev.Left {
+			direction = -1
+		} else if ev.Right {
+			direction = 1
+		}
 
+		// Up button to signal they want to jump.
+		if ev.Up && (s.Player.Grounded() || s.playerJumpCounter >= 0) {
+			jumping = true
+
+			if s.Player.Grounded() {
+				// Allow them to sustain the jump this many ticks.
+				s.playerJumpCounter = 32
+			}
+		}
+
+		// Moving left or right? Interpolate their velocity by acceleration.
+		if direction != 0 {
+			// TODO: fast turn-around if they change directions so they don't
+			// slip and slide while their velocity updates.
+			velocity.X = physics.Lerp(
+				velocity.X,
+				direction*s.playerPhysics.MaxSpeed.X,
+				s.playerPhysics.Acceleration,
+			)
+		} else {
+			// Slow them back to zero using friction.
+			velocity.X = physics.Lerp(
+				velocity.X,
+				0,
+				s.playerPhysics.Friction,
+			)
+		}
+
+		// Moving upwards (jumping): give them full acceleration upwards.
+		if jumping {
+			velocity.Y = -playerSpeed
+		}
+
+		// While in the air, count down their jump counter; when zero they
+		// cannot jump again until they touch ground.
 		if !s.Player.Grounded() {
 			s.playerJumpCounter--
 		}
+	}
 
 	s.Player.SetVelocity(velocity)
 

pkg/scripting/vm.go

@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"git.kirsle.net/apps/doodle/pkg/log"
+	"git.kirsle.net/apps/doodle/pkg/physics"
 	"git.kirsle.net/apps/doodle/pkg/shmem"
 	"git.kirsle.net/go/render"
 	"github.com/robertkrimen/otto"
@@ -73,6 +74,7 @@ func (vm *VM) RegisterLevelHooks() error {
 		"Flash":  shmem.Flash,
 		"RGBA":   render.RGBA,
 		"Point":  render.NewPoint,
+		"Vector": physics.NewVector,
 		"Self":   vm.Self, // i.e., the uix.Actor object
 		"Events": vm.Events,
 		"GetTick": func() uint64 {

pkg/uix/actor.go

@@ -6,9 +6,11 @@ import (
 	"sort"
 	"sync"
 
+	"git.kirsle.net/apps/doodle/pkg/collision"
 	"git.kirsle.net/apps/doodle/pkg/doodads"
 	"git.kirsle.net/apps/doodle/pkg/level"
 	"git.kirsle.net/apps/doodle/pkg/log"
+	"git.kirsle.net/apps/doodle/pkg/physics"
 	"git.kirsle.net/go/render"
 	"github.com/google/uuid"
 	"github.com/robertkrimen/otto"
@@ -23,7 +25,8 @@ import (
 //   as defined in the map: its spawn coordinate and configuration.
 // - A uix.Canvas that can present the actor's graphics to the screen.
 type Actor struct {
-	doodads.Drawing
+	id      string
+	Drawing *doodads.Drawing
 	Actor   *level.Actor
 	Canvas  *Canvas
 
@@ -38,6 +41,11 @@ type Actor struct {
 	inventory  map[string]int    // item inventory. doodad name -> quantity, 0 for key item.
 	data       map[string]string // arbitrary key/value store. DEPRECATED ??
 
+	// Movement data.
+	position render.Point
+	velocity physics.Vector
+	grounded bool
+
 	// Animation variables.
 	animations        map[string]*Animation
 	activeAnimation   *Animation
@@ -81,6 +89,17 @@ func NewActor(id string, levelActor *level.Actor, doodad *doodads.Doodad) *Actor
 	return actor
 }
 
+// ID returns the actor's ID. This is the underlying doodle.Drawing.ID().
+func (a *Actor) ID() string {
+	return a.Drawing.ID()
+}
+
+// Doodad offers access to the underlying Doodad object.
+// Shortcut to the `.Drawing.Doodad` property path.
+func (a *Actor) Doodad() *doodads.Doodad {
+	return a.Drawing.Doodad
+}
+
 // SetGravity configures whether the actor is affected by gravity.
 func (a *Actor) SetGravity(v bool) {
 	a.hasGravity = v
@@ -98,6 +117,46 @@ func (a *Actor) IsMobile() bool {
 	return a.isMobile
 }
 
+// Size returns the size of the actor, from the underlying doodads.Drawing.
+func (a *Actor) Size() render.Rect {
+	return a.Drawing.Size()
+}
+
+// Velocity returns the actor's current velocity vector.
+func (a *Actor) Velocity() physics.Vector {
+	return a.velocity
+}
+
+// SetVelocity updates the actor's velocity vector.
+func (a *Actor) SetVelocity(v physics.Vector) {
+	a.velocity = v
+}
+
+// Position returns the actor's position.
+func (a *Actor) Position() render.Point {
+	return a.position
+}
+
+// MoveTo sets the actor's position.
+func (a *Actor) MoveTo(p render.Point) {
+	a.position = p
+}
+
+// MoveBy adjusts the actor's position.
+func (a *Actor) MoveBy(p render.Point) {
+	a.position.Add(p)
+}
+
+// Grounded returns if the actor is touching a floor.
+func (a *Actor) Grounded() bool {
+	return a.grounded
+}
+
+// SetGrounded sets the actor's grounded value.
+func (a *Actor) SetGrounded(v bool) {
+	a.grounded = v
+}
+
 // SetNoclip sets the noclip setting for an actor. If true, the actor can
 // clip through level geometry.
 func (a *Actor) SetNoclip(v bool) {
@@ -187,7 +246,7 @@ func (a *Actor) Inventory() map[string]int {
 
 // GetBoundingRect gets the bounding box of the actor's doodad.
 func (a *Actor) GetBoundingRect() render.Rect {
-	return doodads.GetBoundingRect(a)
+	return collision.GetBoundingRect(a)
 }
 
 // SetHitbox sets the actor's elected hitbox.
@@ -233,26 +292,26 @@ func (a *Actor) GetData(key string) string {
 
 // LayerCount returns the number of layers in this actor's drawing.
 func (a *Actor) LayerCount() int {
-	return len(a.Doodad.Layers)
+	return len(a.Doodad().Layers)
 }
 
 // ShowLayer sets the actor's ActiveLayer to the index given.
 func (a *Actor) ShowLayer(index int) error {
 	if index < 0 {
 		return errors.New("layer index must be 0 or greater")
-	} else if index > len(a.Doodad.Layers) {
+	} else if index > len(a.Doodad().Layers) {
 		return fmt.Errorf("layer %d out of range for doodad's layers", index)
 	}
 
 	a.activeLayer = index
-	a.Canvas.Load(a.Doodad.Palette, a.Doodad.Layers[index].Chunker)
+	a.Canvas.Load(a.Doodad().Palette, a.Doodad().Layers[index].Chunker)
 	return nil
 }
 
 // ShowLayerNamed sets the actor's ActiveLayer to the one named.
 func (a *Actor) ShowLayerNamed(name string) error {
 	// Find the layer.
-	for i, layer := range a.Doodad.Layers {
+	for i, layer := range a.Doodad().Layers {
 		if layer.Name == name {
 			return a.ShowLayer(i)
 		}

pkg/uix/actor_animation.go

@@ -61,7 +61,7 @@ func (a *Actor) AddAnimation(name string, interval int64, layers []interface{})
 		switch v := name.(type) {
 		case string:
 			var found bool
-			for i, layer := range a.Doodad.Layers {
+			for i, layer := range a.Doodad().Layers {
 				if layer.Name == v {
 					indexes = append(indexes, i)
 					found = true
@@ -80,7 +80,7 @@ func (a *Actor) AddAnimation(name string, interval int64, layers []interface{})
 			}
 
 			iv := int(v)
-			if iv < len(a.Doodad.Layers) {
+			if iv < len(a.Doodad().Layers) {
 				indexes = append(indexes, iv)
 			} else {
 				return fmt.Errorf("layer numbered '%d' is out of bounds", iv)

pkg/uix/actor_collision.go

@@ -7,8 +7,8 @@ import (
 
 	"git.kirsle.net/apps/doodle/pkg/balance"
 	"git.kirsle.net/apps/doodle/pkg/collision"
-	"git.kirsle.net/apps/doodle/pkg/doodads"
 	"git.kirsle.net/apps/doodle/pkg/log"
+	"git.kirsle.net/apps/doodle/pkg/physics"
 	"git.kirsle.net/apps/doodle/pkg/scripting"
 	"git.kirsle.net/go/render"
 	"github.com/robertkrimen/otto"
@@ -63,23 +63,36 @@ func (w *Canvas) loopActorCollision() error {
 
 			// Get the actor's velocity to see if it's moving this tick.
 			v := a.Velocity()
-			if a.hasGravity && v.Y >= 0 {
-				v.Y += balance.Gravity
+
+			// Apply gravity to the actor's velocity.
+			if a.hasGravity && !a.Grounded() { //v.Y >= 0 {
+				if !a.Grounded() {
+					v.Y = physics.Lerp(
+						v.Y,             // current speed
+						balance.Gravity, // target max gravity falling downwards
+						balance.PlayerAcceleration,
+					)
+				} else {
+					v.Y = 0
+				}
+				a.SetVelocity(v)
+				// v.Y += balance.Gravity
 			}
 
 			// If not moving, grab the bounding box right now.
-			if v == render.Origin {
-				boxes[i] = doodads.GetBoundingRect(a)
+			if v.IsZero() {
+				boxes[i] = collision.GetBoundingRect(a)
 				return
 			}
 
 			// Create a delta point from their current location to where they
 			// want to move to this tick.
-			delta := a.Position()
+			delta := physics.VectorFromPoint(a.Position())
 			delta.Add(v)
 
 			// Check collision with level geometry.
-			info, ok := collision.CollidesWithGrid(a, w.chunks, delta)
+			chkPoint := delta.ToPoint()
+			info, ok := collision.CollidesWithGrid(a, w.chunks, chkPoint)
 			if ok {
 				// Collision happened with world.
 				if w.OnLevelCollision != nil {
@@ -89,17 +102,17 @@ func (w *Canvas) loopActorCollision() error {
 
 			// Move us back where the collision check put us
 			if !a.noclip {
-				delta = info.MoveTo
+				delta = physics.VectorFromPoint(info.MoveTo)
 			}
 
 			// Move the actor's World Position to the new location.
-			a.MoveTo(delta)
+			a.MoveTo(delta.ToPoint())
 
 			// Keep the actor from leaving the world borders of bounded maps.
 			w.loopContainActorsInsideLevel(a)
 
 			// Store this actor's bounding box after they've moved.
-			boxes[i] = doodads.GetBoundingRect(a)
+			boxes[i] = collision.GetBoundingRect(a)
 		}(i, a)
 		wg.Wait()
 	}
@@ -115,10 +128,12 @@ func (w *Canvas) loopActorCollision() error {
 
 		collidingActors[a.ID()] = b.ID()
 
+		// log.Error("between boxes: %+v  <%s> <%s>", tuple, a.ID(), b.ID())
+
 		// Call the OnCollide handler for A informing them of B's intersection.
 		if w.scripting != nil {
 			var (
-				rect        = doodads.GetBoundingRect(b)
+				rect        = collision.GetBoundingRect(b)
 				lastGoodBox = render.Rect{
 					X: originalPositions[b.ID()].X,
 					Y: originalPositions[b.ID()].Y,
@@ -190,7 +205,7 @@ func (w *Canvas) loopActorCollision() error {
 						// Did A protest?
 						if err == scripting.ErrReturnFalse {
 							// Are they on top?
-							aHitbox := doodads.GetBoundingRectHitbox(a, a.Hitbox())
+							aHitbox := collision.GetBoundingRectHitbox(a.Drawing, a.Hitbox())
 							if render.AbsInt(test.Y+test.H-aHitbox.Y) == 0 {
 								onTop = true
 								onTopY = test.Y
@@ -241,7 +256,7 @@ func (w *Canvas) loopActorCollision() error {
 				log.Error(
 					"ERROR: Actors %s and %s overlap and the script returned false,"+
 						"but I didn't store %s original position earlier??",
-					a.Doodad.Title, b.Doodad.Title, b.Doodad.Title,
+					a.Doodad().Title, b.Doodad().Title, b.Doodad().Title,
 				)
 			}
 

pkg/uix/canvas_actors.go

@@ -58,7 +58,7 @@ func (w *Canvas) InstallScripts() error {
 		vm.Self = actor
 		vm.Set("Self", vm.Self)
 
-		if _, err := vm.Run(actor.Doodad.Script); err != nil {
+		if _, err := vm.Run(actor.Doodad().Script); err != nil {
 			log.Error("Run script for actor %s failed: %s", actor.ID(), err)
 		}
 

pkg/uix/canvas_link_tool.go

@@ -19,7 +19,7 @@ func (w *Canvas) LinkAdd(a *Actor) error {
 		// First click, hold onto this actor.
 		w.linkFirst = a
 		shmem.Flash("Doodad '%s' selected, click the next Doodad to link it to",
-			a.Doodad.Title,
+			a.Doodad().Title,
 		)
 	} else {
 		// Second click, call the OnLinkActors handler with the two actors.