After commit c018f5fd29 Fenrir is being switched over to go. If you do not want to be part of the testing process, please switch to master.

internal/console/decode_linux.go

@@ -0,0 +1,78 @@
+// Fenrir console screen reader.
+// Copyright (c) 2026 Storm Dragon
+// SPDX-License-Identifier: GPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by the Free
+// Software Foundation, either version 3 of the License, or (at your option)
+// any later version.
+//
+// This program is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+// more details.
+//
+// You should have received a copy of the GNU General Public License along with
+// this program. If not, see <https://www.gnu.org/licenses/gpl-3.0.html>.
+
+//go:build linux && cgo
+
+package console
+
+import (
+	"encoding/binary"
+	"fmt"
+	"unicode/utf8"
+
+	"git.stormux.org/storm/fenrir/internal/screen"
+)
+
+// decode_snapshot uses the VCSA header and native-endian UTF-32 VCSU cells. Glyph
+// numbers from VCSA are deliberately not treated as Unicode characters.
+func decode_snapshot(tty int, header, text []byte) (screen.Snapshot, error) {
+	if len(header) < 4 {
+		return screen.Snapshot{}, fmt.Errorf("short VCSA header")
+	}
+	snapshot := screen.Snapshot{Terminal: tty, Active: true, Rows: int(header[0]), Cols: int(header[1]), X: int(header[2]), Y: int(header[3])}
+	if snapshot.Rows == 0 || snapshot.Cols == 0 || snapshot.X >= snapshot.Cols || snapshot.Y >= snapshot.Rows {
+		return screen.Snapshot{}, fmt.Errorf("invalid console geometry or cursor")
+	}
+	count := snapshot.Rows * snapshot.Cols
+	if len(text) != count*4 {
+		return screen.Snapshot{}, fmt.Errorf("VCSU size %d does not match %dx%d console", len(text), snapshot.Cols, snapshot.Rows)
+	}
+	snapshot.Cells = make([]rune, count)
+	for index := range snapshot.Cells {
+		value := binary.NativeEndian.Uint32(text[index*4:])
+		switch {
+		case value == 0:
+			snapshot.Cells[index] = ' '
+		case value > utf8.MaxRune || value >= 0xd800 && value <= 0xdfff:
+			snapshot.Cells[index] = utf8.RuneError
+		default:
+			snapshot.Cells[index] = rune(value)
+		}
+	}
+	return snapshot, nil
+}
+
+func decode_attributes(snapshot *screen.Snapshot, data []byte) error {
+	if len(data) != 4+len(snapshot.Cells)*2 {
+		return fmt.Errorf("VCSA size %d does not match %dx%d console", len(data), snapshot.Cols, snapshot.Rows)
+	}
+	snapshot.Attributes = make([]screen.Attribute, len(snapshot.Cells))
+	for index := range snapshot.Attributes {
+		// VCSA stores native-endian glyph/attribute words. Glyph bytes remain
+		// unused: Unicode always comes from VCSU, including non-ASCII fonts.
+		attribute := binary.NativeEndian.Uint16(data[4+index*2:]) >> 8
+		// VGA palette order swaps ANSI red/blue. Intensity is a color, not
+		// proof of bold; VCSA cannot recover the original SGR font styles.
+		ansi := func(value uint16) uint32 { return uint32(value&10 | (value&1)<<2 | (value&4)>>2) }
+		style := uint32(0)
+		if attribute&128 != 0 {
+			style = screen.ConsoleHigh
+		}
+		snapshot.Attributes[index] = screen.Attribute{Foreground: screen.ColorIndexed | ansi(attribute&15), Background: screen.ColorIndexed | ansi((attribute>>4)&7), Style: style}
+	}
+	return nil
+}