better and easier to understand asset loading

assets/loader-sprites.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"image"
 	_ "image/png"
+	"io/fs"
 	"log"
 	"log/slog"
 	"path"
@@ -17,6 +18,11 @@ import (
 // Maps image name to image data
 type AssetRegistry map[string]*ebiten.Image
 
+// A helper to pass the registry easier around
+type assetData struct {
+	Registry AssetRegistry
+}
+
 type AnimationGeo struct {
 	X      int `json:"x"`
 	Y      int `json:"y"`
@@ -52,13 +58,15 @@ type AnimationRegistry map[string]AnimationSet
 //go:embed sprites/*.png fonts/*.ttf levels/*.ldtk shaders/*.kg sprites/*.json
 var assetfs embed.FS
 
+// Called at build time, creates the global asset and animation registries
 var Assets, Animations = LoadImages()
 
+// load pngs and json files
 func LoadImages() (AssetRegistry, AnimationRegistry) {
 	dir := "sprites"
-	images := AssetRegistry{}
+	imagedata := &assetData{}
+	imagedata.Registry = AssetRegistry{}
 	rawanimations := []AnimationJSON{}
-	animations := AnimationRegistry{}
 
 	// we use embed.FS to iterate over all files in ./assets/
 	entries, err := assetfs.ReadDir(dir)
@@ -69,14 +77,32 @@ func LoadImages() (AssetRegistry, AnimationRegistry) {
 	for _, imagefile := range entries {
 		path := path.Join(dir, imagefile.Name())
 
-		switch {
-		case strings.HasSuffix(path, ".png"):
 		fd, err := assetfs.Open(path)
 		if err != nil {
-				log.Fatalf("failed to open image file %s: %s", imagefile.Name(), err)
+			log.Fatalf("failed to open file %s: %s", imagefile.Name(), err)
 		}
 		defer fd.Close()
 
+		switch {
+		case strings.HasSuffix(path, ".png"):
+			name, image := ReadImage(imagefile, fd)
+			imagedata.Registry[name] = image
+
+		case strings.HasSuffix(path, ".json"):
+			animationjson := ReadJson(imagefile, fd)
+			rawanimations = append(rawanimations, animationjson)
+		}
+
+		slog.Debug("loaded asset", "path", path)
+	}
+
+	// preprocess animation sprites
+	animations := ProcessAnimations(rawanimations, imagedata)
+
+	return imagedata.Registry, animations
+}
+
+func ReadImage(imagefile fs.DirEntry, fd fs.File) (string, *ebiten.Image) {
 	name := strings.TrimSuffix(imagefile.Name(), ".png")
 
 	img, _, err := image.Decode(fd)
@@ -84,38 +110,42 @@ func LoadImages() (AssetRegistry, AnimationRegistry) {
 		log.Fatalf("failed to decode image %s: %s", imagefile.Name(), err)
 	}
 
-			images[name] = ebiten.NewImageFromImage(img)
+	image := ebiten.NewImageFromImage(img)
 
-			slog.Debug("loaded asset", "path", path)
-		case strings.HasSuffix(path, ".json"):
-			fd, err := assetfs.Open(path)
-			if err != nil {
-				log.Fatalf("failed to open json file %s: %s", imagefile.Name(), err)
+	return name, image
 }
-			defer fd.Close()
 
+func ReadJson(imagefile fs.DirEntry, fd fs.File) AnimationJSON {
 	buf := new(bytes.Buffer)
 	buf.ReadFrom(fd)
 
 	animationjson := AnimationJSON{}
 
-			err = json.Unmarshal(buf.Bytes(), &animationjson)
+	err := json.Unmarshal(buf.Bytes(), &animationjson)
 	if err != nil {
 		log.Fatalf("failed to parse JSON: %s", err)
 	}
 
-			rawanimations = append(rawanimations, animationjson)
-		}
+	return animationjson
 }
 
-	// preprocess animation sprites
+// turn a  raw JSON from  Asesprite into  something we can  use better
+// internally we  also load all the  sprites of an animation  by using
+// image.SubImage() on the spriteset matching the animation name.
+// so, if the animation JSON is called "player-idle.json", then we
+// expect to receive the spriteset in a file "player-idle.png", which
+// has of course already been loaded at this stage. These spritesets
+// must contain a row of sprites. We get the measurements from the JSON.
+func ProcessAnimations(rawanimations []AnimationJSON, imagedata *assetData) AnimationRegistry {
+	animations := AnimationRegistry{}
+
 	for _, animation := range rawanimations {
 		animationset := AnimationSet{}
 
 		animationset.File = strings.TrimSuffix(animation.Meta.Name, ".png")
 
 		for _, frame := range animation.Frames {
-			sprite := images[animationset.File].SubImage(
+			sprite := imagedata.Registry[animationset.File].SubImage(
 				image.Rect(
 					frame.Position.X,
 					frame.Position.Y,
@@ -132,5 +162,5 @@ func LoadImages() (AssetRegistry, AnimationRegistry) {
 		animations[animationset.File] = animationset
 	}
 
-	return images, animations
+	return animations
 }