Anim

engine/anim.go

@@ -0,0 +1,40 @@
+package engine
+
+// Anim is an "instance" of an AnimDef: an animation being displayed,
+// together with the current state.
+type Anim struct {
+	Def          *AnimDef
+	CurrentIndex int
+	CurrentTicks int
+}
+
+func (a *Anim) CurrentFrame() int { return a.Def.Frames[a.CurrentIndex].Frame }
+
+// Update increments the tick count and advances the frame if necessary.
+func (a *Anim) Update() error {
+	a.CurrentTicks++
+	if !a.Def.Loop && a.CurrentIndex == len(a.Def.Frames)-1 {
+		// on the last frame of a one shot so remain on final frame
+		return nil
+	}
+	if a.CurrentTicks >= a.Def.Frames[a.CurrentIndex].DurationTicks {
+		a.CurrentTicks = 0
+		a.CurrentIndex++
+	}
+	if a.Def.Loop && a.CurrentIndex >= len(a.Def.Frames) {
+		a.CurrentIndex = 0
+	}
+	return nil
+}
+
+// AnimDef describes an animation (sequence of frames and timings).
+type AnimDef struct {
+	Frames []AnimFrame `json:"frames"`
+	Loop   bool        `json:"loop"`
+}
+
+// AnimFrame describes a frame in an animation.
+type AnimFrame struct {
+	Frame         int `json:"frame"`    // show this frame
+	DurationTicks int `json:"duration"` // for this long
+}

engine/asset.go

@@ -14,12 +14,23 @@ var (
 	imageCache = make(map[string]*ebiten.Image)
 )
 
+type AnimRef struct {
+	Path string
+
+	animdef *AnimDef
+}
+
+// ImageRef loads images from the AssetFS into *ebiten.Image form.
+// It is your responsibility to import _ "image/..." for whatever
+// format the files are in.
 type ImageRef struct {
 	Path string
 
 	image *ebiten.Image
 }
 
+// Image returns the image. If it hasn't been loaded yet, it loads.
+// Multiple distinct ImageRefs can use the same path.
 func (r *ImageRef) Image() (*ebiten.Image, error) {
 	if r.image != nil {
 		return r.image, nil

engine/tiles.go

@@ -63,26 +63,7 @@ type StaticTile int
 func (s StaticTile) TileIndex() int { return int(s) }
 
 type AnimatedTile struct {
-	Frame         int // index into AnimDef
+	Anim
-	DurationTicks int // time spent showing current frame
-	AnimDef       []TileAnimFrameDef
 }
 
-func (a *AnimatedTile) TileIndex() int { return a.AnimDef[a.Frame].Tile }
+func (a *AnimatedTile) TileIndex() int { return a.CurrentFrame() }
-
-func (a *AnimatedTile) Update() error {
-	a.DurationTicks++
-	if a.DurationTicks >= a.AnimDef[a.Frame].DurationTicks {
-		a.DurationTicks = 0
-		a.Frame++
-	}
-	if a.Frame >= len(a.AnimDef) {
-		a.Frame = 0
-	}
-	return nil
-}
-
-type TileAnimFrameDef struct {
-	Tile          int // show this tile
-	DurationTicks int // show it for this long
-}

main.go

@@ -47,18 +47,28 @@ func main() {
 	}
 
 	tiles[4][5] = &engine.AnimatedTile{
-		AnimDef: []engine.TileAnimFrameDef{
+		Anim: engine.Anim{
-			{Tile: 0, DurationTicks: 16},
+			Def: &engine.AnimDef{
-			{Tile: 1, DurationTicks: 16},
+				Frames: []engine.AnimFrame{
-			{Tile: 2, DurationTicks: 16},
+					{Frame: 0, DurationTicks: 16},
+					{Frame: 1, DurationTicks: 16},
+					{Frame: 2, DurationTicks: 16},
+				},
+				Loop: true,
+			},
 		},
 	}
 	tiles[6][7] = &engine.AnimatedTile{
-		AnimDef: []engine.TileAnimFrameDef{
+		Anim: engine.Anim{
-			{Tile: 3, DurationTicks: 12},
+			Def: &engine.AnimDef{
-			{Tile: 4, DurationTicks: 12},
+				Frames: []engine.AnimFrame{
-			{Tile: 5, DurationTicks: 12},
+					{Frame: 3, DurationTicks: 12},
-			{Tile: 6, DurationTicks: 12},
+					{Frame: 4, DurationTicks: 12},
+					{Frame: 5, DurationTicks: 12},
+					{Frame: 6, DurationTicks: 12},
+				},
+				Loop: true,
+			},
 		},
 	}