Refactor runner and installation scripts for improved functionality

- Removed the `--disable-hiprt` flag from the runner command, simplifying the rendering options for users.
- Updated the `jiggablend-runner` script and README to reflect the removal of the HIPRT control flag, enhancing clarity in usage instructions.
- Enhanced the installation script to provide clearer examples for running the jiggablend manager and runner, improving user experience during setup.
- Implemented a more robust GPU backend detection mechanism, allowing for better compatibility with various hardware configurations.

pkg/blendfile/version.go

@@ -0,0 +1,123 @@
+package blendfile
+
+import (
+	"compress/gzip"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+)
+
+// ParseVersionFromReader parses the Blender version from a reader.
+// Returns major and minor version numbers.
+//
+// Blend file header layout (12 bytes):
+//
+//	"BLENDER" (7) + pointer-size (1: '-'=64, '_'=32) + endian (1: 'v'=LE, 'V'=BE)
+//	+ version (3 digits, e.g. "402" = 4.02)
+//
+// Supports uncompressed, gzip-compressed, and zstd-compressed blend files.
+func ParseVersionFromReader(r io.ReadSeeker) (major, minor int, err error) {
+	header := make([]byte, 12)
+	n, err := r.Read(header)
+	if err != nil || n < 12 {
+		return 0, 0, fmt.Errorf("failed to read blend file header: %w", err)
+	}
+
+	if string(header[:7]) != "BLENDER" {
+		r.Seek(0, 0)
+		return parseCompressedVersion(r)
+	}
+
+	return parseVersionDigits(header[9:12])
+}
+
+// ParseVersionFromFile opens a blend file and parses the Blender version.
+func ParseVersionFromFile(blendPath string) (major, minor int, err error) {
+	file, err := os.Open(blendPath)
+	if err != nil {
+		return 0, 0, fmt.Errorf("failed to open blend file: %w", err)
+	}
+	defer file.Close()
+
+	return ParseVersionFromReader(file)
+}
+
+// VersionString returns a formatted version string like "4.2".
+func VersionString(major, minor int) string {
+	return fmt.Sprintf("%d.%d", major, minor)
+}
+
+func parseVersionDigits(versionBytes []byte) (major, minor int, err error) {
+	if len(versionBytes) != 3 {
+		return 0, 0, fmt.Errorf("expected 3 version digits, got %d", len(versionBytes))
+	}
+	fmt.Sscanf(string(versionBytes[0]), "%d", &major)
+	fmt.Sscanf(string(versionBytes[1:3]), "%d", &minor)
+	return major, minor, nil
+}
+
+func parseCompressedVersion(r io.ReadSeeker) (major, minor int, err error) {
+	magic := make([]byte, 4)
+	if _, err := r.Read(magic); err != nil {
+		return 0, 0, err
+	}
+	r.Seek(0, 0)
+
+	// gzip: 0x1f 0x8b
+	if magic[0] == 0x1f && magic[1] == 0x8b {
+		gzReader, err := gzip.NewReader(r)
+		if err != nil {
+			return 0, 0, fmt.Errorf("failed to create gzip reader: %w", err)
+		}
+		defer gzReader.Close()
+
+		header := make([]byte, 12)
+		n, err := gzReader.Read(header)
+		if err != nil || n < 12 {
+			return 0, 0, fmt.Errorf("failed to read compressed blend header: %w", err)
+		}
+		if string(header[:7]) != "BLENDER" {
+			return 0, 0, fmt.Errorf("invalid blend file format")
+		}
+		return parseVersionDigits(header[9:12])
+	}
+
+	// zstd: 0x28 0xB5 0x2F 0xFD
+	if magic[0] == 0x28 && magic[1] == 0xb5 && magic[2] == 0x2f && magic[3] == 0xfd {
+		return parseZstdVersion(r)
+	}
+
+	return 0, 0, fmt.Errorf("unknown blend file format")
+}
+
+func parseZstdVersion(r io.ReadSeeker) (major, minor int, err error) {
+	r.Seek(0, 0)
+
+	cmd := exec.Command("zstd", "-d", "-c")
+	cmd.Stdin = r
+
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		return 0, 0, fmt.Errorf("failed to create zstd stdout pipe: %w", err)
+	}
+
+	if err := cmd.Start(); err != nil {
+		return 0, 0, fmt.Errorf("failed to start zstd decompression: %w", err)
+	}
+
+	header := make([]byte, 12)
+	n, readErr := io.ReadFull(stdout, header)
+
+	cmd.Process.Kill()
+	cmd.Wait()
+
+	if readErr != nil || n < 12 {
+		return 0, 0, fmt.Errorf("failed to read zstd compressed blend header: %v", readErr)
+	}
+	if string(header[:7]) != "BLENDER" {
+		return 0, 0, fmt.Errorf("invalid blend file format in zstd archive")
+	}
+
+	return parseVersionDigits(header[9:12])
+}