assets builder tools (#39)

Reviewed-on: #39
Reviewed-by: xtul <mpiasecki720@protonmail.com>

internal/assets/convert.go

@@ -0,0 +1,116 @@
+package assets
+
+import (
+	"flag"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+var textureExts = map[string]bool{".dds": true, ".png": true, ".tga": true}
+
+// runConvert converts textures in place, flipping vertically exactly once per
+// conversion. --to defaults to dds. Files already in the target format are
+// skipped.
+func runConvert(args []string, stdout, stderr io.Writer) int {
+	fs := flag.NewFlagSet("convert", flag.ContinueOnError)
+	fs.SetOutput(stderr)
+	to := fs.String("to", "dds", "target format: dds|png|tga")
+	backend := fs.String("backend", "magick", "ImageMagick-compatible binary")
+	nonRecursive := fs.Bool("non-recursive", false, "do not descend into subdirectories")
+	if err := fs.Parse(args); err != nil {
+		return exitUsage
+	}
+	target := strings.ToLower(*to)
+	if target != "dds" && target != "png" && target != "tga" {
+		fmt.Fprintln(stderr, "assets convert: --to must be dds, png, or tga")
+		return exitUsage
+	}
+	dirs := fs.Args()
+	if len(dirs) == 0 {
+		fmt.Fprintln(stderr, "assets convert: usage: convert [--to dds|png|tga] <dir>...")
+		return exitUsage
+	}
+
+	magick := look(*backend)
+	if magick == "" {
+		fmt.Fprintf(stderr, "assets convert: backend %q not found — install ImageMagick (magick)\n", *backend)
+		return exitTool
+	}
+
+	files, err := walk(dirs, textureExts, !*nonRecursive)
+	if err != nil {
+		fmt.Fprintln(stderr, "assets convert:", err)
+		return exitUsage
+	}
+
+	targetExt := "." + target
+	failed := false
+	for _, src := range files {
+		srcExt := strings.ToLower(filepath.Ext(src))
+		if srcExt == targetExt {
+			continue // already in the target format
+		}
+		dst := strings.TrimSuffix(src, filepath.Ext(src)) + targetExt
+		var convErr error
+		if target == "dds" {
+			convErr = pngToDDS(magick, src, dst)
+		} else {
+			convErr = ddsToPNG(magick, src, dst) // works for any decodable source
+		}
+		if convErr != nil {
+			fmt.Fprintf(stderr, "assets convert: %s: %v\n", src, convErr)
+			failed = true
+			continue
+		}
+		if dst != src {
+			if err := os.Remove(src); err != nil {
+				fmt.Fprintf(stderr, "assets convert: %s: %v\n", src, err)
+				failed = true
+			}
+		}
+	}
+	if failed {
+		return exitFail
+	}
+	return exitOK
+}
+
+// ddsToPNG decodes src to dst (PNG/TGA by dst's extension), flipping vertically
+// once. The single flip is the defining NWN behavior.
+func ddsToPNG(magickBin, src, dst string) error {
+	if out, err := runner("", nil, magickBin, src, "-flip", dst); err != nil {
+		return fmt.Errorf("magick: %v: %s", err, strings.TrimSpace(string(out)))
+	}
+	return nil
+}
+
+// pngToDDS encodes src to a DDS at dst, flipping vertically once and choosing
+// DXT1 for opaque images, DXT5 for images with alpha.
+func pngToDDS(magickBin, src, dst string) error {
+	compression := "dxt1"
+	if hasAlpha(magickBin, src) {
+		compression = "dxt5"
+	}
+	// ponytail: mipmaps rely on magick's default full chain (NWN wants a
+	// pyramid, which magick writes by default). Add `-define dds:mipmaps=N`
+	// here if a specific count is ever required.
+	out, err := runner("", nil, magickBin, src, "-flip",
+		"-define", "dds:compression="+compression, dst)
+	if err != nil {
+		return fmt.Errorf("magick: %v: %s", err, strings.TrimSpace(string(out)))
+	}
+	return nil
+}
+
+// hasAlpha reports whether src has any non-opaque pixel, via `magick identify`.
+// On any probe error it assumes alpha (DXT5), the safe/lossless-alpha default.
+func hasAlpha(magickBin, src string) bool {
+	out, err := runner("", nil, magickBin, "identify", "-format", "%[opaque]", src)
+	if err != nil {
+		return true
+	}
+	return !strings.EqualFold(strings.TrimSpace(string(out)), "true")
+}