vesa_tty - VESA bitmap-font text renderer

Header: kernel/include/kernel/vesa_tty.h
Source: kernel/arch/i386/vesa_tty.c
Font data: kernel/include/kernel/vesa_font.h

Renders text onto the VESA linear framebuffer using the built-in 8×8 bitmap font (FONT8x8). Every glyph is scaled 2× (FONT_SCALE = 2), producing 16×16 cell characters for improved legibility at typical VESA resolutions.

This renderer runs in parallel with the VGA text-mode terminal: every character written via the tty driver is also forwarded here, so both outputs show identical content.

Geometry

Symbol Formula Typical value (1024×768)
FONT_CELL_W 8 × FONT_SCALE = 16 px 16 px
FONT_CELL_H 8 × FONT_SCALE = 16 px 16 px
tty_cols fb.width / FONT_CELL_W 64 columns
tty_rows fb.height / FONT_CELL_H 48 rows

Functions

vesa_tty_init 

bool vesa_tty_init(void);
  1. Call vesa_get_fb() - returns false immediately if no framebuffer is available.
  2. Call paging_map_region() to map the framebuffer physical address range into the virtual address space before any pixel write.
  3. Compute tty_cols and tty_rows from the framebuffer dimensions.
  4. Set foreground to white (0xFFFFFF) and background to black (0x000000).
  5. Call vesa_clear(tty_bg) to erase any BIOS/bootloader splash.
  6. Mark the renderer as ready.

Must be called after vesa_init() and paging_init().

vesa_tty_is_ready 

bool vesa_tty_is_ready(void);

Return true once vesa_tty_init() has completed successfully. All other vesa_tty_* functions check this flag and return immediately if not ready, making them safe to call at any point during boot.

vesa_tty_putchar 

void vesa_tty_putchar(char c);

Render character c at the current cursor position and advance the cursor.

  • '\n' - move to column 0 of the next row; scroll up one row if the cursor reaches the bottom.
  • '\r' - move to column 0 of the current row.
  • '\b' - erase the character to the left of the cursor (draw a space).
  • Any other character - draw the glyph and advance the column; wrap to the next row at the right edge, scrolling if necessary.

vesa_tty_setcolor 

void vesa_tty_setcolor(uint32_t fg_rgb, uint32_t bg_rgb);

Set the foreground and background colours as 24-bit 0x00RRGGBB values. The colours are converted to the framebuffer’s native packed format via the RGB shift fields in vesa_fb_t.

vesa_tty_put_at 

void vesa_tty_put_at(char c, uint32_t col, uint32_t row);

Draw character c at cell (col, row) without moving the cursor. Used by the spinner animation. Out-of-bounds cell coordinates are silently ignored.

vesa_tty_spinner_tick 

void vesa_tty_spinner_tick(uint32_t tick);

Draw one frame of a four-character spinner (|, /, -, \) at the top-right corner of the display. The frame advances every 12 ticks. Mirrors t_spinner_tick() on the VESA display.

vesa_tty_paint_status (makmux bar) 

void vesa_tty_paint_status(int active, int count);

Paints the status bar on the reserved bottom row (the multiplexer is named makmux; the bar shows the OS name): a fixed-width left label, the centred VT1 VT2 VT3 VT4 indicators (1-based, matching Alt+F1–F4, with slot active highlighted black-on-yellow), and the Alt+F1-F4 hint on the right. Driven by vtty on register / switch-drain / clear. vesa_tty_set_status_visible() hides it during the boot loading screen.

Status-bar clock (Alt+F5) 

void vesa_tty_toggle_clock(void);              /* Alt+F5 toggles the label   */
void vesa_tty_status_clock_tick(uint32_t tick); /* timer hook, refresh once/s */

The left label is a fixed 18-column slot (so the centred VT indicators never shift) that toggles between Makar and a live CMOS-RTC clock HH:MM:SS DD/MM/YY on Alt+F5. While the clock is showing, vesa_tty_status_clock_tick — registered as a timer per-tick hook — repaints just that field once per second.

Caret style 

void     vesa_tty_set_caret_style(uint32_t style);  /* 0 = line, 2 = flashing block */
uint32_t vesa_tty_get_caret_style(void);

Selects the on-screen caret. Userspace reaches this via SYS_CARET_STYLE (218), which returns the previous style so an app (e.g. vix.elf) can request a flashing block caret while editing and restore the default on exit. No-op in VGA-text mode.

Scrolling

When the cursor moves past the last row, scroll_up() shifts all pixel rows up by FONT_CELL_H scanlines using memcpy, then clears the bottom character row. This is a simple pixel-copy scroll with no hardware acceleration.

Future work

  • Hardware cursor overlay or a software block cursor to show the text insertion point.
  • Colour attributes per character cell (already supported by vesa_tty_setcolor globally; needs per-cell storage).
  • Scalable or anti-aliased fonts (TrueType / SFN) for higher-resolution displays.
  • Optimised scroll using REP MOVSD or the framebuffer’s hardware scroll register where available.