sow-tools/internal/assets/convert.go

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")
}