feat: graphical framebuffer support for VGA driver

When GRUB is configured with multiboot2, it may provide a graphical
(RGB) framebuffer instead of legacy VGA text mode. This happens on
UTM/QEMU on macOS and other configurations where the bootloader
switches to a pixel-based display.

- Parse multiboot2 framebuffer tag in kernel_main to detect display mode
- Identity-map the framebuffer address (often at 0xFD000000+) after
  paging is enabled, with write-through caching
- Add framebuffer.h describing the boot-time display info
- Embed 8x16 VGA bitmap font (font8x16.h) for pixel-mode rendering
- Rewrite VGA driver to support both text mode and pixel mode:
  - Text mode: unchanged behavior writing to 0xB8000
  - Pixel mode: renders characters using the bitmap font to the
    GRUB-provided framebuffer, with proper VGA color palette mapping
  - Auto-detects mode from fb_info at init time
- Multiboot2 header now requests text mode via framebuffer tag, but
  gracefully falls back to pixel rendering if GRUB provides RGB
- Reverted grub.cfg gfxpayload=text (caused display issues on UTM)

Tested: boots in both text mode and graphical framebuffer mode.

CMakeLists.txt

@@ -38,7 +38,7 @@ add_custom_command(
 add_custom_target(initrd DEPENDS ${INITRD_FILE})
 
 # Create grub.cfg for ISO - includes module2 for the initrd
-file(WRITE ${CMAKE_BINARY_DIR}/isodir/boot/grub/grub.cfg "set timeout=0\nset default=0\nsearch --set=root --file /boot/kernel.bin\nmenuentry \"ClaudeOS\" {\n  set gfxpayload=text\n  multiboot2 /boot/kernel.bin\n  module2 /boot/initrd.cpio\n}")
+file(WRITE ${CMAKE_BINARY_DIR}/isodir/boot/grub/grub.cfg "set timeout=0\nset default=0\nsearch --set=root --file /boot/kernel.bin\nmenuentry \"ClaudeOS\" {\n  multiboot2 /boot/kernel.bin\n  module2 /boot/initrd.cpio\n}")
 
 
 # ISO Generation

src/font8x16.h

@@ -0,0 +1,215 @@
+/**
+ * @file font8x16.h
+ * @brief Embedded 8x16 VGA bitmap font for graphical framebuffer rendering.
+ *
+ * Each character is 16 bytes: one byte per scanline, MSB is leftmost pixel.
+ * Covers ASCII 32 (space) through 126 (~). Characters outside this range
+ * render as a filled block.
+ *
+ * This is the standard VGA 8x16 font data, in the public domain.
+ */
+
+#ifndef FONT8X16_H
+#define FONT8X16_H
+
+#include <stdint.h>
+
+#define FONT_WIDTH  8
+#define FONT_HEIGHT 16
+#define FONT_FIRST  32
+#define FONT_LAST   126
+
+static const uint8_t font8x16_data[][16] = {
+    /* 32: space */
+    {0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00},
+    /* 33: ! */
+    {0x00,0x00,0x18,0x3C,0x3C,0x3C,0x18,0x18,0x18,0x00,0x18,0x18,0x00,0x00,0x00,0x00},
+    /* 34: " */
+    {0x00,0x66,0x66,0x66,0x24,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00},
+    /* 35: # */
+    {0x00,0x00,0x00,0x6C,0x6C,0xFE,0x6C,0x6C,0x6C,0xFE,0x6C,0x6C,0x00,0x00,0x00,0x00},
+    /* 36: $ */
+    {0x18,0x18,0x7C,0xC6,0xC2,0xC0,0x7C,0x06,0x06,0x86,0xC6,0x7C,0x18,0x18,0x00,0x00},
+    /* 37: % */
+    {0x00,0x00,0x00,0x00,0xC2,0xC6,0x0C,0x18,0x30,0x60,0xC6,0x86,0x00,0x00,0x00,0x00},
+    /* 38: & */
+    {0x00,0x00,0x38,0x6C,0x6C,0x38,0x76,0xDC,0xCC,0xCC,0xCC,0x76,0x00,0x00,0x00,0x00},
+    /* 39: ' */
+    {0x00,0x30,0x30,0x30,0x60,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00},
+    /* 40: ( */
+    {0x00,0x00,0x0C,0x18,0x30,0x30,0x30,0x30,0x30,0x30,0x18,0x0C,0x00,0x00,0x00,0x00},
+    /* 41: ) */
+    {0x00,0x00,0x30,0x18,0x0C,0x0C,0x0C,0x0C,0x0C,0x0C,0x18,0x30,0x00,0x00,0x00,0x00},
+    /* 42: * */
+    {0x00,0x00,0x00,0x00,0x00,0x66,0x3C,0xFF,0x3C,0x66,0x00,0x00,0x00,0x00,0x00,0x00},
+    /* 43: + */
+    {0x00,0x00,0x00,0x00,0x00,0x18,0x18,0x7E,0x18,0x18,0x00,0x00,0x00,0x00,0x00,0x00},
+    /* 44: , */
+    {0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x18,0x18,0x18,0x30,0x00,0x00,0x00},
+    /* 45: - */
+    {0x00,0x00,0x00,0x00,0x00,0x00,0x00,0xFE,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00},
+    /* 46: . */
+    {0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x18,0x18,0x00,0x00,0x00,0x00},
+    /* 47: / */
+    {0x00,0x00,0x00,0x00,0x02,0x06,0x0C,0x18,0x30,0x60,0xC0,0x80,0x00,0x00,0x00,0x00},
+    /* 48: 0 */
+    {0x00,0x00,0x3C,0x66,0xC3,0xC3,0xDB,0xDB,0xC3,0xC3,0x66,0x3C,0x00,0x00,0x00,0x00},
+    /* 49: 1 */
+    {0x00,0x00,0x18,0x38,0x78,0x18,0x18,0x18,0x18,0x18,0x18,0x7E,0x00,0x00,0x00,0x00},
+    /* 50: 2 */
+    {0x00,0x00,0x7C,0xC6,0x06,0x0C,0x18,0x30,0x60,0xC0,0xC6,0xFE,0x00,0x00,0x00,0x00},
+    /* 51: 3 */
+    {0x00,0x00,0x7C,0xC6,0x06,0x06,0x3C,0x06,0x06,0x06,0xC6,0x7C,0x00,0x00,0x00,0x00},
+    /* 52: 4 */
+    {0x00,0x00,0x0C,0x1C,0x3C,0x6C,0xCC,0xFE,0x0C,0x0C,0x0C,0x1E,0x00,0x00,0x00,0x00},
+    /* 53: 5 */
+    {0x00,0x00,0xFE,0xC0,0xC0,0xC0,0xFC,0x06,0x06,0x06,0xC6,0x7C,0x00,0x00,0x00,0x00},
+    /* 54: 6 */
+    {0x00,0x00,0x38,0x60,0xC0,0xC0,0xFC,0xC6,0xC6,0xC6,0xC6,0x7C,0x00,0x00,0x00,0x00},
+    /* 55: 7 */
+    {0x00,0x00,0xFE,0xC6,0x06,0x06,0x0C,0x18,0x30,0x30,0x30,0x30,0x00,0x00,0x00,0x00},
+    /* 56: 8 */
+    {0x00,0x00,0x7C,0xC6,0xC6,0xC6,0x7C,0xC6,0xC6,0xC6,0xC6,0x7C,0x00,0x00,0x00,0x00},
+    /* 57: 9 */
+    {0x00,0x00,0x7C,0xC6,0xC6,0xC6,0x7E,0x06,0x06,0x06,0x0C,0x78,0x00,0x00,0x00,0x00},
+    /* 58: : */
+    {0x00,0x00,0x00,0x00,0x18,0x18,0x00,0x00,0x00,0x18,0x18,0x00,0x00,0x00,0x00,0x00},
+    /* 59: ; */
+    {0x00,0x00,0x00,0x00,0x18,0x18,0x00,0x00,0x00,0x18,0x18,0x30,0x00,0x00,0x00,0x00},
+    /* 60: < */
+    {0x00,0x00,0x00,0x06,0x0C,0x18,0x30,0x60,0x30,0x18,0x0C,0x06,0x00,0x00,0x00,0x00},
+    /* 61: = */
+    {0x00,0x00,0x00,0x00,0x00,0x7E,0x00,0x00,0x7E,0x00,0x00,0x00,0x00,0x00,0x00,0x00},
+    /* 62: > */
+    {0x00,0x00,0x00,0x60,0x30,0x18,0x0C,0x06,0x0C,0x18,0x30,0x60,0x00,0x00,0x00,0x00},
+    /* 63: ? */
+    {0x00,0x00,0x7C,0xC6,0xC6,0x0C,0x18,0x18,0x18,0x00,0x18,0x18,0x00,0x00,0x00,0x00},
+    /* 64: @ */
+    {0x00,0x00,0x00,0x7C,0xC6,0xC6,0xDE,0xDE,0xDE,0xDC,0xC0,0x7C,0x00,0x00,0x00,0x00},
+    /* 65: A */
+    {0x00,0x00,0x10,0x38,0x6C,0xC6,0xC6,0xFE,0xC6,0xC6,0xC6,0xC6,0x00,0x00,0x00,0x00},
+    /* 66: B */
+    {0x00,0x00,0xFC,0x66,0x66,0x66,0x7C,0x66,0x66,0x66,0x66,0xFC,0x00,0x00,0x00,0x00},
+    /* 67: C */
+    {0x00,0x00,0x3C,0x66,0xC2,0xC0,0xC0,0xC0,0xC0,0xC2,0x66,0x3C,0x00,0x00,0x00,0x00},
+    /* 68: D */
+    {0x00,0x00,0xF8,0x6C,0x66,0x66,0x66,0x66,0x66,0x66,0x6C,0xF8,0x00,0x00,0x00,0x00},
+    /* 69: E */
+    {0x00,0x00,0xFE,0x66,0x62,0x68,0x78,0x68,0x60,0x62,0x66,0xFE,0x00,0x00,0x00,0x00},
+    /* 70: F */
+    {0x00,0x00,0xFE,0x66,0x62,0x68,0x78,0x68,0x60,0x60,0x60,0xF0,0x00,0x00,0x00,0x00},
+    /* 71: G */
+    {0x00,0x00,0x3C,0x66,0xC2,0xC0,0xC0,0xDE,0xC6,0xC6,0x66,0x3A,0x00,0x00,0x00,0x00},
+    /* 72: H */
+    {0x00,0x00,0xC6,0xC6,0xC6,0xC6,0xFE,0xC6,0xC6,0xC6,0xC6,0xC6,0x00,0x00,0x00,0x00},
+    /* 73: I */
+    {0x00,0x00,0x3C,0x18,0x18,0x18,0x18,0x18,0x18,0x18,0x18,0x3C,0x00,0x00,0x00,0x00},
+    /* 74: J */
+    {0x00,0x00,0x1E,0x0C,0x0C,0x0C,0x0C,0x0C,0xCC,0xCC,0xCC,0x78,0x00,0x00,0x00,0x00},
+    /* 75: K */
+    {0x00,0x00,0xE6,0x66,0x66,0x6C,0x78,0x78,0x6C,0x66,0x66,0xE6,0x00,0x00,0x00,0x00},
+    /* 76: L */
+    {0x00,0x00,0xF0,0x60,0x60,0x60,0x60,0x60,0x60,0x62,0x66,0xFE,0x00,0x00,0x00,0x00},
+    /* 77: M */
+    {0x00,0x00,0xC6,0xEE,0xFE,0xFE,0xD6,0xC6,0xC6,0xC6,0xC6,0xC6,0x00,0x00,0x00,0x00},
+    /* 78: N */
+    {0x00,0x00,0xC6,0xE6,0xF6,0xFE,0xDE,0xCE,0xC6,0xC6,0xC6,0xC6,0x00,0x00,0x00,0x00},
+    /* 79: O */
+    {0x00,0x00,0x7C,0xC6,0xC6,0xC6,0xC6,0xC6,0xC6,0xC6,0xC6,0x7C,0x00,0x00,0x00,0x00},
+    /* 80: P */
+    {0x00,0x00,0xFC,0x66,0x66,0x66,0x7C,0x60,0x60,0x60,0x60,0xF0,0x00,0x00,0x00,0x00},
+    /* 81: Q */
+    {0x00,0x00,0x7C,0xC6,0xC6,0xC6,0xC6,0xC6,0xC6,0xD6,0xDE,0x7C,0x0C,0x0E,0x00,0x00},
+    /* 82: R */
+    {0x00,0x00,0xFC,0x66,0x66,0x66,0x7C,0x6C,0x66,0x66,0x66,0xE6,0x00,0x00,0x00,0x00},
+    /* 83: S */
+    {0x00,0x00,0x7C,0xC6,0xC6,0x60,0x38,0x0C,0x06,0xC6,0xC6,0x7C,0x00,0x00,0x00,0x00},
+    /* 84: T */
+    {0x00,0x00,0xFF,0xDB,0x99,0x18,0x18,0x18,0x18,0x18,0x18,0x3C,0x00,0x00,0x00,0x00},
+    /* 85: U */
+    {0x00,0x00,0xC6,0xC6,0xC6,0xC6,0xC6,0xC6,0xC6,0xC6,0xC6,0x7C,0x00,0x00,0x00,0x00},
+    /* 86: V */
+    {0x00,0x00,0xC6,0xC6,0xC6,0xC6,0xC6,0xC6,0xC6,0x6C,0x38,0x10,0x00,0x00,0x00,0x00},
+    /* 87: W */
+    {0x00,0x00,0xC6,0xC6,0xC6,0xC6,0xD6,0xD6,0xD6,0xFE,0xEE,0x6C,0x00,0x00,0x00,0x00},
+    /* 88: X */
+    {0x00,0x00,0xC6,0xC6,0x6C,0x7C,0x38,0x38,0x7C,0x6C,0xC6,0xC6,0x00,0x00,0x00,0x00},
+    /* 89: Y */
+    {0x00,0x00,0xC3,0xC3,0x66,0x3C,0x18,0x18,0x18,0x18,0x18,0x3C,0x00,0x00,0x00,0x00},
+    /* 90: Z */
+    {0x00,0x00,0xFE,0xC6,0x86,0x0C,0x18,0x30,0x60,0xC2,0xC6,0xFE,0x00,0x00,0x00,0x00},
+    /* 91: [ */
+    {0x00,0x00,0x3C,0x30,0x30,0x30,0x30,0x30,0x30,0x30,0x30,0x3C,0x00,0x00,0x00,0x00},
+    /* 92: \ */
+    {0x00,0x00,0x00,0x80,0xC0,0xE0,0x70,0x38,0x1C,0x0E,0x06,0x02,0x00,0x00,0x00,0x00},
+    /* 93: ] */
+    {0x00,0x00,0x3C,0x0C,0x0C,0x0C,0x0C,0x0C,0x0C,0x0C,0x0C,0x3C,0x00,0x00,0x00,0x00},
+    /* 94: ^ */
+    {0x10,0x38,0x6C,0xC6,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00},
+    /* 95: _ */
+    {0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0xFF,0x00,0x00},
+    /* 96: ` */
+    {0x30,0x30,0x18,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00},
+    /* 97: a */
+    {0x00,0x00,0x00,0x00,0x00,0x78,0x0C,0x7C,0xCC,0xCC,0xCC,0x76,0x00,0x00,0x00,0x00},
+    /* 98: b */
+    {0x00,0x00,0xE0,0x60,0x60,0x78,0x6C,0x66,0x66,0x66,0x66,0x7C,0x00,0x00,0x00,0x00},
+    /* 99: c */
+    {0x00,0x00,0x00,0x00,0x00,0x7C,0xC6,0xC0,0xC0,0xC0,0xC6,0x7C,0x00,0x00,0x00,0x00},
+    /* 100: d */
+    {0x00,0x00,0x1C,0x0C,0x0C,0x3C,0x6C,0xCC,0xCC,0xCC,0xCC,0x76,0x00,0x00,0x00,0x00},
+    /* 101: e */
+    {0x00,0x00,0x00,0x00,0x00,0x7C,0xC6,0xFE,0xC0,0xC0,0xC6,0x7C,0x00,0x00,0x00,0x00},
+    /* 102: f */
+    {0x00,0x00,0x1C,0x36,0x32,0x30,0x78,0x30,0x30,0x30,0x30,0x78,0x00,0x00,0x00,0x00},
+    /* 103: g */
+    {0x00,0x00,0x00,0x00,0x00,0x76,0xCC,0xCC,0xCC,0xCC,0x7C,0x0C,0xCC,0x78,0x00,0x00},
+    /* 104: h */
+    {0x00,0x00,0xE0,0x60,0x60,0x6C,0x76,0x66,0x66,0x66,0x66,0xE6,0x00,0x00,0x00,0x00},
+    /* 105: i */
+    {0x00,0x00,0x18,0x18,0x00,0x38,0x18,0x18,0x18,0x18,0x18,0x3C,0x00,0x00,0x00,0x00},
+    /* 106: j */
+    {0x00,0x00,0x06,0x06,0x00,0x0E,0x06,0x06,0x06,0x06,0x06,0x06,0x66,0x3C,0x00,0x00},
+    /* 107: k */
+    {0x00,0x00,0xE0,0x60,0x60,0x66,0x6C,0x78,0x78,0x6C,0x66,0xE6,0x00,0x00,0x00,0x00},
+    /* 108: l */
+    {0x00,0x00,0x38,0x18,0x18,0x18,0x18,0x18,0x18,0x18,0x18,0x3C,0x00,0x00,0x00,0x00},
+    /* 109: m */
+    {0x00,0x00,0x00,0x00,0x00,0xE6,0xFF,0xDB,0xDB,0xDB,0xDB,0xDB,0x00,0x00,0x00,0x00},
+    /* 110: n */
+    {0x00,0x00,0x00,0x00,0x00,0xDC,0x66,0x66,0x66,0x66,0x66,0x66,0x00,0x00,0x00,0x00},
+    /* 111: o */
+    {0x00,0x00,0x00,0x00,0x00,0x7C,0xC6,0xC6,0xC6,0xC6,0xC6,0x7C,0x00,0x00,0x00,0x00},
+    /* 112: p */
+    {0x00,0x00,0x00,0x00,0x00,0xDC,0x66,0x66,0x66,0x66,0x7C,0x60,0x60,0xF0,0x00,0x00},
+    /* 113: q */
+    {0x00,0x00,0x00,0x00,0x00,0x76,0xCC,0xCC,0xCC,0xCC,0x7C,0x0C,0x0C,0x1E,0x00,0x00},
+    /* 114: r */
+    {0x00,0x00,0x00,0x00,0x00,0xDC,0x76,0x66,0x60,0x60,0x60,0xF0,0x00,0x00,0x00,0x00},
+    /* 115: s */
+    {0x00,0x00,0x00,0x00,0x00,0x7C,0xC6,0x60,0x38,0x0C,0xC6,0x7C,0x00,0x00,0x00,0x00},
+    /* 116: t */
+    {0x00,0x00,0x10,0x30,0x30,0xFC,0x30,0x30,0x30,0x30,0x36,0x1C,0x00,0x00,0x00,0x00},
+    /* 117: u */
+    {0x00,0x00,0x00,0x00,0x00,0xCC,0xCC,0xCC,0xCC,0xCC,0xCC,0x76,0x00,0x00,0x00,0x00},
+    /* 118: v */
+    {0x00,0x00,0x00,0x00,0x00,0xC3,0xC3,0xC3,0xC3,0x66,0x3C,0x18,0x00,0x00,0x00,0x00},
+    /* 119: w */
+    {0x00,0x00,0x00,0x00,0x00,0xC6,0xC6,0xC6,0xD6,0xD6,0xFE,0x6C,0x00,0x00,0x00,0x00},
+    /* 120: x */
+    {0x00,0x00,0x00,0x00,0x00,0xC6,0x6C,0x38,0x38,0x38,0x6C,0xC6,0x00,0x00,0x00,0x00},
+    /* 121: y */
+    {0x00,0x00,0x00,0x00,0x00,0xC6,0xC6,0xC6,0xC6,0xC6,0x7E,0x06,0x0C,0xF8,0x00,0x00},
+    /* 122: z */
+    {0x00,0x00,0x00,0x00,0x00,0xFE,0xCC,0x18,0x30,0x60,0xC6,0xFE,0x00,0x00,0x00,0x00},
+    /* 123: { */
+    {0x00,0x00,0x0E,0x18,0x18,0x18,0x70,0x18,0x18,0x18,0x18,0x0E,0x00,0x00,0x00,0x00},
+    /* 124: | */
+    {0x00,0x00,0x18,0x18,0x18,0x18,0x00,0x18,0x18,0x18,0x18,0x18,0x00,0x00,0x00,0x00},
+    /* 125: } */
+    {0x00,0x00,0x70,0x18,0x18,0x18,0x0E,0x18,0x18,0x18,0x18,0x70,0x00,0x00,0x00,0x00},
+    /* 126: ~ */
+    {0x00,0x00,0x76,0xDC,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00},
+};
+
+#endif /* FONT8X16_H */

src/framebuffer.h

@@ -0,0 +1,44 @@
+/**
+ * @file framebuffer.h
+ * @brief Framebuffer information from the bootloader.
+ *
+ * Stores the display mode and framebuffer address provided by GRUB
+ * via the multiboot2 framebuffer tag. The VGA driver uses this to
+ * decide between text-mode writes (0xB8000) and pixel rendering.
+ */
+
+#ifndef FRAMEBUFFER_H
+#define FRAMEBUFFER_H
+
+#include <stdint.h>
+
+/** Framebuffer types (matches multiboot2 definitions). */
+#define FB_TYPE_INDEXED  0
+#define FB_TYPE_RGB      1
+#define FB_TYPE_EGA_TEXT 2
+
+/**
+ * Framebuffer information structure.
+ * Populated during boot from the multiboot2 framebuffer tag.
+ */
+typedef struct {
+    uint32_t addr;         /**< Physical address of the framebuffer. */
+    uint32_t pitch;        /**< Bytes per scanline. */
+    uint32_t width;        /**< Width in pixels (or columns for text). */
+    uint32_t height;       /**< Height in pixels (or rows for text). */
+    uint8_t  bpp;          /**< Bits per pixel. */
+    uint8_t  type;         /**< FB_TYPE_RGB, FB_TYPE_EGA_TEXT, etc. */
+
+    /* RGB field positions (only valid when type == FB_TYPE_RGB). */
+    uint8_t  red_pos;
+    uint8_t  red_size;
+    uint8_t  green_pos;
+    uint8_t  green_size;
+    uint8_t  blue_pos;
+    uint8_t  blue_size;
+} framebuffer_info_t;
+
+/** Global framebuffer info, filled by kernel_main. */
+extern framebuffer_info_t fb_info;
+
+#endif /* FRAMEBUFFER_H */

src/kernel.c

@@ -1,6 +1,7 @@
 #include <multiboot2.h>
 #include <stdint.h>
 #include <stddef.h>
+#include <string.h>
 #include "gdt.h"
 #include "idt.h"
 #include "pic.h"
@@ -17,6 +18,10 @@
 #include "vfs.h"
 #include "initrd_fs.h"
 #include "keyboard.h"
+#include "framebuffer.h"
+
+/* Global framebuffer info, parsed from multiboot2 tags. */
+framebuffer_info_t fb_info;
 
 void offset_print(const char *str)
 {
@@ -60,8 +65,9 @@ void kernel_main(uint32_t magic, uint32_t addr) {
     init_pmm(addr);
     offset_print("PMM initialized\n");
 
-    /* Scan Multiboot2 tags for the initrd module */
+    /* Scan Multiboot2 tags for the initrd module and framebuffer info */
     uint32_t initrd_start = 0, initrd_end = 0;
+    memset(&fb_info, 0, sizeof(fb_info));
     {
         struct multiboot_tag *tag;
         for (tag = (struct multiboot_tag *)(addr + 8);
@@ -75,7 +81,36 @@ void kernel_main(uint32_t magic, uint32_t addr) {
                 print_hex(initrd_start);
                 offset_print(" to ");
                 print_hex(initrd_end);
-                break; /* Use first module */
+            }
+            if (tag->type == MULTIBOOT_TAG_TYPE_FRAMEBUFFER) {
+                struct multiboot_tag_framebuffer *fbt =
+                    (struct multiboot_tag_framebuffer *)tag;
+                fb_info.addr   = (uint32_t)fbt->common.framebuffer_addr;
+                fb_info.pitch  = fbt->common.framebuffer_pitch;
+                fb_info.width  = fbt->common.framebuffer_width;
+                fb_info.height = fbt->common.framebuffer_height;
+                fb_info.bpp    = fbt->common.framebuffer_bpp;
+                fb_info.type   = fbt->common.framebuffer_type;
+
+                if (fb_info.type == FB_TYPE_RGB) {
+                    fb_info.red_pos    = fbt->framebuffer_red_field_position;
+                    fb_info.red_size   = fbt->framebuffer_red_mask_size;
+                    fb_info.green_pos  = fbt->framebuffer_green_field_position;
+                    fb_info.green_size = fbt->framebuffer_green_mask_size;
+                    fb_info.blue_pos   = fbt->framebuffer_blue_field_position;
+                    fb_info.blue_size  = fbt->framebuffer_blue_mask_size;
+                }
+
+                offset_print("Framebuffer: type=");
+                print_hex(fb_info.type);
+                offset_print("  addr=");
+                print_hex(fb_info.addr);
+                offset_print("  ");
+                print_hex(fb_info.width);
+                offset_print("  x ");
+                print_hex(fb_info.height);
+                offset_print("  bpp=");
+                print_hex(fb_info.bpp);
             }
         }
     }
@@ -83,6 +118,21 @@ void kernel_main(uint32_t magic, uint32_t addr) {
     init_paging();
     offset_print("Paging initialized\n");
 
+    /* If GRUB provided a graphical framebuffer, identity-map it so
+     * the VGA driver can write pixels to it after paging is enabled. */
+    if (fb_info.addr != 0 && fb_info.type == FB_TYPE_RGB) {
+        uint32_t fb_size = fb_info.pitch * fb_info.height;
+        uint32_t fb_base = fb_info.addr & ~0xFFFu; /* page-align down */
+        uint32_t fb_end  = (fb_info.addr + fb_size + 0xFFF) & ~0xFFFu;
+        offset_print("  Mapping framebuffer ");
+        print_hex(fb_base);
+        offset_print("  to ");
+        print_hex(fb_end);
+        for (uint32_t pa = fb_base; pa < fb_end; pa += 4096) {
+            paging_map_page(pa, pa, PAGE_PRESENT | PAGE_WRITE | PAGE_WRITETHROUGH);
+        }
+    }
+
     /* Test paging: allocate a page and write to it */
     void *test_page = paging_alloc_page();
     if (test_page) {

src/vga.c

@@ -1,10 +1,14 @@
 /**
  * @file vga.c
- * @brief VGA text-mode driver implementation.
+ * @brief Display driver supporting both VGA text mode and graphical framebuffer.
  *
- * Drives the standard VGA text-mode framebuffer at 0xB8000. The buffer
+ * Supports two modes depending on what GRUB provides:
- * is an array of 80×25 16-bit values, where the low byte is the ASCII
+ *   - EGA text mode: writes character+attribute pairs to the text buffer
- * character and the high byte encodes foreground and background color.
+ *   - Graphical (RGB) framebuffer: renders an embedded 8x16 bitmap font
+ *     to the pixel framebuffer provided by GRUB
+ *
+ * The mode is detected at init time from the global fb_info structure,
+ * which kernel_main populates from the multiboot2 framebuffer tag.
  *
  * This driver registers itself via the REGISTER_DRIVER macro and is
  * automatically discovered during boot.
@@ -14,122 +18,295 @@
 #include "driver.h"
 #include "port_io.h"
 #include "pmm.h"
+#include "framebuffer.h"
+#include "font8x16.h"
+#include <string.h>
 
-/** Base address of the VGA text-mode framebuffer. */
+/* Debug helpers defined in kernel.c */
-#define VGA_BUFFER 0xB8000
+extern void offset_print(const char *str);
+extern void print_hex(uint32_t val);
 
-/** Pointer to the VGA framebuffer, treated as an array of uint16_t. */
+/* ================================================================
-static uint16_t *vga_buffer = (uint16_t *)VGA_BUFFER;
+ * Common state
+ * ================================================================ */
 
-/** Current cursor row (0-based). */
+/** Current text cursor position. */
-static uint8_t cursor_row = 0;
+static uint32_t cursor_row = 0;
+static uint32_t cursor_col = 0;
 
-/** Current cursor column (0-based). */
+/** Columns and rows of the text grid. */
-static uint8_t cursor_col = 0;
+static uint32_t text_cols = 80;
+static uint32_t text_rows = 25;
 
-/** Current text attribute byte (foreground | background << 4). */
+/** Current color attribute (foreground | background << 4). */
-static uint8_t text_attr = 0;
+static uint8_t text_attr = 0x07;
+
+/** Display mode: 0 = text, 1 = pixel. */
+static int display_mode = 0;
+
+/* ================================================================
+ * Text mode (EGA) internals
+ * ================================================================ */
+
+/** VGA text-mode framebuffer default base. */
+#define VGA_TEXT_BUFFER 0xB8000
+static uint16_t *text_buffer = (uint16_t *)VGA_TEXT_BUFFER;
 
-/**
- * Create a VGA entry (character + attribute) for the framebuffer.
- *
- * @param c    ASCII character.
- * @param attr Color attribute byte.
- * @return     16-bit VGA entry.
- */
 static inline uint16_t vga_entry(char c, uint8_t attr) {
     return (uint16_t)c | ((uint16_t)attr << 8);
 }
 
-/**
+static void text_update_cursor(void) {
- * Create a color attribute byte from foreground and background colors.
+    uint16_t pos = (uint16_t)(cursor_row * text_cols + cursor_col);
- *
- * @param fg Foreground color (0–15).
- * @param bg Background color (0–15).
- * @return   Attribute byte.
- */
-static inline uint8_t vga_color(vga_color_t fg, vga_color_t bg) {
-    return (uint8_t)fg | ((uint8_t)bg << 4);
-}
-
-/**
- * Update the hardware cursor position via VGA I/O ports.
- */
-static void update_cursor(void) {
-    uint16_t pos = cursor_row * VGA_WIDTH + cursor_col;
-
     outb(0x3D4, 0x0F);
     outb(0x3D5, (uint8_t)(pos & 0xFF));
     outb(0x3D4, 0x0E);
     outb(0x3D5, (uint8_t)((pos >> 8) & 0xFF));
 }
 
-/**
+static void text_scroll(void) {
- * Scroll the screen up by one line.
+    for (uint32_t i = 0; i < (text_rows - 1) * text_cols; i++) {
- *
+        text_buffer[i] = text_buffer[i + text_cols];
- * The top line is discarded, all other lines move up, and the bottom
- * line is filled with spaces.
- */
-static void scroll(void) {
-    /* Move all lines up by one */
-    for (int i = 0; i < (VGA_HEIGHT - 1) * VGA_WIDTH; i++) {
-        vga_buffer[i] = vga_buffer[i + VGA_WIDTH];
     }
-
-    /* Clear the last line */
     uint16_t blank = vga_entry(' ', text_attr);
-    for (int i = (VGA_HEIGHT - 1) * VGA_WIDTH; i < VGA_HEIGHT * VGA_WIDTH; i++) {
+    for (uint32_t i = (text_rows - 1) * text_cols; i < text_rows * text_cols; i++) {
-        vga_buffer[i] = blank;
+        text_buffer[i] = blank;
+    }
+    cursor_row = text_rows - 1;
 }
 
-    cursor_row = VGA_HEIGHT - 1;
+static void text_clear(void) {
-}
-
-void vga_clear(void) {
     uint16_t blank = vga_entry(' ', text_attr);
-    for (int i = 0; i < VGA_WIDTH * VGA_HEIGHT; i++) {
+    for (uint32_t i = 0; i < text_cols * text_rows; i++) {
-        vga_buffer[i] = blank;
+        text_buffer[i] = blank;
     }
     cursor_row = 0;
     cursor_col = 0;
-    update_cursor();
+    text_update_cursor();
 }
 
-void vga_set_color(vga_color_t fg, vga_color_t bg) {
+static void text_putchar(char c) {
-    text_attr = vga_color(fg, bg);
-}
-
-void vga_putchar(char c) {
     if (c == '\n') {
         cursor_col = 0;
         cursor_row++;
     } else if (c == '\r') {
         cursor_col = 0;
     } else if (c == '\t') {
-        cursor_col = (cursor_col + 8) & ~7;
+        cursor_col = (cursor_col + 8) & ~7u;
-        if (cursor_col >= VGA_WIDTH) {
+        if (cursor_col >= text_cols) {
             cursor_col = 0;
             cursor_row++;
         }
     } else if (c == '\b') {
         if (cursor_col > 0) {
             cursor_col--;
-            vga_buffer[cursor_row * VGA_WIDTH + cursor_col] = vga_entry(' ', text_attr);
+            text_buffer[cursor_row * text_cols + cursor_col] = vga_entry(' ', text_attr);
         }
     } else {
-        vga_buffer[cursor_row * VGA_WIDTH + cursor_col] = vga_entry(c, text_attr);
+        text_buffer[cursor_row * text_cols + cursor_col] = vga_entry(c, text_attr);
         cursor_col++;
-        if (cursor_col >= VGA_WIDTH) {
+        if (cursor_col >= text_cols) {
             cursor_col = 0;
             cursor_row++;
         }
     }
-
+    if (cursor_row >= text_rows) {
-    if (cursor_row >= VGA_HEIGHT) {
+        text_scroll();
-        scroll();
+    }
+    text_update_cursor();
 }
 
-    update_cursor();
+/* ================================================================
+ * Pixel mode (graphical framebuffer) internals
+ * ================================================================ */
+
+/** Pointer to the pixel framebuffer. */
+static uint8_t *pixel_fb = (uint8_t *)0;
+
+/** Framebuffer parameters. */
+static uint32_t fb_pitch  = 0;
+static uint32_t fb_width  = 0;
+static uint32_t fb_height = 0;
+static uint32_t fb_bpp    = 0;
+
+/** RGB field info. */
+static uint8_t fb_red_pos   = 16, fb_red_size   = 8;
+static uint8_t fb_green_pos =  8, fb_green_size = 8;
+static uint8_t fb_blue_pos  =  0, fb_blue_size  = 8;
+
+/**
+ * Pack an RGB color into the framebuffer's native pixel format.
+ */
+static inline uint32_t pack_color(uint8_t r, uint8_t g, uint8_t b) {
+    (void)fb_red_size; (void)fb_green_size; (void)fb_blue_size;
+    return ((uint32_t)r << fb_red_pos) |
+           ((uint32_t)g << fb_green_pos) |
+           ((uint32_t)b << fb_blue_pos);
+}
+
+/**
+ * Set a single pixel in the framebuffer.
+ */
+static inline void pixel_set(uint32_t x, uint32_t y, uint32_t color) {
+    if (x >= fb_width || y >= fb_height) return;
+    uint32_t offset = y * fb_pitch + x * (fb_bpp / 8);
+    uint32_t bytes = fb_bpp / 8;
+
+    if (bytes == 4) {
+        *(volatile uint32_t *)(pixel_fb + offset) = color;
+    } else if (bytes == 3) {
+        pixel_fb[offset]     = (uint8_t)(color & 0xFF);
+        pixel_fb[offset + 1] = (uint8_t)((color >> 8) & 0xFF);
+        pixel_fb[offset + 2] = (uint8_t)((color >> 16) & 0xFF);
+    } else if (bytes == 2) {
+        *(volatile uint16_t *)(pixel_fb + offset) = (uint16_t)color;
+    }
+}
+
+/**
+ * VGA color index to 24-bit RGB mapping.
+ */
+static const uint32_t vga_palette[16] = {
+    0x000000, /* 0  black */
+    0x0000AA, /* 1  blue */
+    0x00AA00, /* 2  green */
+    0x00AAAA, /* 3  cyan */
+    0xAA0000, /* 4  red */
+    0xAA00AA, /* 5  magenta */
+    0xAA5500, /* 6  brown */
+    0xAAAAAA, /* 7  light grey */
+    0x555555, /* 8  dark grey */
+    0x5555FF, /* 9  light blue */
+    0x55FF55, /* 10 light green */
+    0x55FFFF, /* 11 light cyan */
+    0xFF5555, /* 12 light red */
+    0xFF55FF, /* 13 light magenta */
+    0xFFFF55, /* 14 yellow */
+    0xFFFFFF, /* 15 white */
+};
+
+/**
+ * Get packed foreground/background colors from text_attr.
+ */
+static void attr_to_colors(uint32_t *fg_out, uint32_t *bg_out) {
+    uint8_t fg_idx = text_attr & 0x0F;
+    uint8_t bg_idx = (text_attr >> 4) & 0x0F;
+    uint32_t fg_rgb = vga_palette[fg_idx];
+    uint32_t bg_rgb = vga_palette[bg_idx];
+    *fg_out = pack_color((fg_rgb >> 16) & 0xFF, (fg_rgb >> 8) & 0xFF, fg_rgb & 0xFF);
+    *bg_out = pack_color((bg_rgb >> 16) & 0xFF, (bg_rgb >> 8) & 0xFF, bg_rgb & 0xFF);
+}
+
+/**
+ * Render a single glyph at character grid position (col, row).
+ */
+static void pixel_render_char(uint32_t col, uint32_t row, char c) {
+    uint32_t fg, bg;
+    attr_to_colors(&fg, &bg);
+
+    const uint8_t *glyph;
+    if (c >= FONT_FIRST && c <= FONT_LAST) {
+        glyph = font8x16_data[c - FONT_FIRST];
+    } else {
+        glyph = 0; /* NULL = solid block for unknown chars */
+    }
+
+    uint32_t px = col * FONT_WIDTH;
+    uint32_t py = row * FONT_HEIGHT;
+
+    for (uint32_t y = 0; y < FONT_HEIGHT; y++) {
+        uint8_t bits = glyph ? glyph[y] : 0xFF;
+        for (uint32_t x = 0; x < FONT_WIDTH; x++) {
+            uint32_t color = (bits & (0x80 >> x)) ? fg : bg;
+            pixel_set(px + x, py + y, color);
+        }
+    }
+}
+
+/**
+ * Scroll the pixel framebuffer up by one text row (FONT_HEIGHT pixels).
+ */
+static void pixel_scroll(void) {
+    uint32_t row_bytes = FONT_HEIGHT * fb_pitch;
+    uint32_t total_text_bytes = text_rows * row_bytes;
+
+    /* Move all rows up by one */
+    memcpy(pixel_fb, pixel_fb + row_bytes, total_text_bytes - row_bytes);
+
+    /* Clear the last text row */
+    uint32_t dummy, bg;
+    attr_to_colors(&dummy, &bg);
+    uint32_t last_row_y = (text_rows - 1) * FONT_HEIGHT;
+    for (uint32_t y = last_row_y; y < last_row_y + FONT_HEIGHT; y++) {
+        for (uint32_t x = 0; x < text_cols * FONT_WIDTH; x++) {
+            pixel_set(x, y, bg);
+        }
+    }
+    cursor_row = text_rows - 1;
+}
+
+static void pixel_clear(void) {
+    uint32_t dummy, bg;
+    attr_to_colors(&dummy, &bg);
+    for (uint32_t y = 0; y < fb_height; y++) {
+        for (uint32_t x = 0; x < fb_width; x++) {
+            pixel_set(x, y, bg);
+        }
+    }
+    cursor_row = 0;
+    cursor_col = 0;
+}
+
+static void pixel_putchar(char c) {
+    if (c == '\n') {
+        cursor_col = 0;
+        cursor_row++;
+    } else if (c == '\r') {
+        cursor_col = 0;
+    } else if (c == '\t') {
+        cursor_col = (cursor_col + 8) & ~7u;
+        if (cursor_col >= text_cols) {
+            cursor_col = 0;
+            cursor_row++;
+        }
+    } else if (c == '\b') {
+        if (cursor_col > 0) {
+            cursor_col--;
+            pixel_render_char(cursor_col, cursor_row, ' ');
+        }
+    } else {
+        pixel_render_char(cursor_col, cursor_row, c);
+        cursor_col++;
+        if (cursor_col >= text_cols) {
+            cursor_col = 0;
+            cursor_row++;
+        }
+    }
+    if (cursor_row >= text_rows) {
+        pixel_scroll();
+    }
+}
+
+/* ================================================================
+ * Public interface
+ * ================================================================ */
+
+void vga_clear(void) {
+    if (display_mode == 0)
+        text_clear();
+    else
+        pixel_clear();
+}
+
+void vga_set_color(vga_color_t fg, vga_color_t bg) {
+    text_attr = (uint8_t)fg | ((uint8_t)bg << 4);
+}
+
+void vga_putchar(char c) {
+    if (display_mode == 0)
+        text_putchar(c);
+    else
+        pixel_putchar(c);
 }
 
 void vga_puts(const char *str) {
@@ -153,21 +330,19 @@ void vga_put_dec(uint32_t val) {
         vga_putchar('0');
         return;
     }
-
     char buf[12];
     int pos = 0;
     while (val > 0) {
         buf[pos++] = '0' + (val % 10);
         val /= 10;
     }
-    /* Print in reverse */
     while (pos > 0) {
         vga_putchar(buf[--pos]);
     }
 }
 
 void vga_show_mem_stats(void) {
-    uint32_t mem_kb = pmm_get_memory_size() + 1024; /* total including lower */
+    uint32_t mem_kb = pmm_get_memory_size() + 1024;
 
     vga_set_color(VGA_LIGHT_CYAN, VGA_BLACK);
     vga_puts("=== ClaudeOS Memory Statistics ===\n");
@@ -199,18 +374,75 @@ void vga_show_mem_stats(void) {
     vga_set_color(VGA_LIGHT_GREY, VGA_BLACK);
 }
 
-/* --- Driver registration --- */
+/* ================================================================
+ * Driver registration
+ * ================================================================ */
 
-/**
- * VGA probe: always succeeds since VGA text mode is always available
- * on the target platform (i386).
- */
 static driver_probe_result_t vga_probe(void) {
     return DRIVER_PROBE_OK;
 }
 
 int vga_init(void) {
-    text_attr = vga_color(VGA_LIGHT_GREY, VGA_BLACK);
+    text_attr = (uint8_t)VGA_LIGHT_GREY | ((uint8_t)VGA_BLACK << 4);
+
+    if (fb_info.type == FB_TYPE_EGA_TEXT || fb_info.addr == 0) {
+        /* Text mode (or no framebuffer tag — assume legacy text mode) */
+        display_mode = 0;
+        text_cols = 80;
+        text_rows = 25;
+
+        if (fb_info.addr != 0) {
+            text_buffer = (uint16_t *)(uint32_t)fb_info.addr;
+            text_cols = fb_info.width;
+            text_rows = fb_info.height;
+        }
+
+        offset_print("  VGA: text mode ");
+        print_hex(text_cols);
+        offset_print("  VGA: x ");
+        print_hex(text_rows);
+    } else if (fb_info.type == FB_TYPE_RGB) {
+        /* Graphical framebuffer — render with bitmap font */
+        display_mode = 1;
+        pixel_fb   = (uint8_t *)(uint32_t)fb_info.addr;
+        fb_pitch   = fb_info.pitch;
+        fb_width   = fb_info.width;
+        fb_height  = fb_info.height;
+        fb_bpp     = fb_info.bpp;
+
+        fb_red_pos     = fb_info.red_pos;
+        fb_red_size    = fb_info.red_size;
+        fb_green_pos   = fb_info.green_pos;
+        fb_green_size  = fb_info.green_size;
+        fb_blue_pos    = fb_info.blue_pos;
+        fb_blue_size   = fb_info.blue_size;
+
+        /* Calculate text grid from pixel dimensions */
+        text_cols = fb_width / FONT_WIDTH;
+        text_rows = fb_height / FONT_HEIGHT;
+        if (text_cols == 0) text_cols = 1;
+        if (text_rows == 0) text_rows = 1;
+
+        offset_print("  VGA: pixel mode ");
+        print_hex(fb_width);
+        offset_print("  VGA: x ");
+        print_hex(fb_height);
+        offset_print("  VGA: bpp=");
+        print_hex(fb_bpp);
+        offset_print("  VGA: text grid ");
+        print_hex(text_cols);
+        offset_print("  VGA: x ");
+        print_hex(text_rows);
+        offset_print("  VGA: addr=");
+        print_hex((uint32_t)pixel_fb);
+    } else {
+        /* Indexed or unknown — fall back to text mode */
+        display_mode = 0;
+        text_cols = 80;
+        text_rows = 25;
+        offset_print("  VGA: unknown fb type, assuming text mode\n");
+    }
+
     vga_clear();
 
     vga_set_color(VGA_LIGHT_GREEN, VGA_BLACK);