Module fbcon 

Framebuffer console (fbcon) — text rendering onto a pixel framebuffer.

Renders characters using the 8x16 bitmap font onto the UEFI-provided (or ramfb-provided) pixel framebuffer. Supports cursor tracking, newlines, tab stops, backspace, scrolling, and basic ANSI color escape sequences.

Performance architecture

Three-layer pipeline with eager rendering, glyph cache, and incremental dirty-row blitting:

1. Text cell grid — character/color pairs in a ring buffer. Scrolling is O(cols) (advance ring pointer + clear one row of cells).
2. RAM back-buffer — always in sync via eager rendering (each glyph rendered to pixels immediately on write). Scrolling uses a simple memmove (~1ms in RAM) and marks all rows dirty (dirty_all). A glyph cache pre-renders all 256 glyphs as u32 pixel arrays for the current color pair, making glyph rendering a copy_nonoverlapping of 32 bytes per row.
3. Hardware framebuffer — MMIO memory. Touched once per flush() call, only for dirty rows — typically one row (~80KB) instead of the full screen (~4MB). On x86_64, write-combining (PAT) provides faster MMIO writes.

Thread-safety: The global FBCON is protected by a spinlock. Interrupt handlers must NOT call _fbcon_print (use raw serial output for diagnostics in ISRs).

Structs

FbHwInfo

Framebuffer hardware information for the compositor.

FramebufferConsole

Framebuffer console state.

Enums

FbPixelFormat

Pixel format of the framebuffer.

Functions

_fbcon_print

Print formatted text to the framebuffer console.

cursor_row

Return the current text cursor row (for targeted row flushing).

disable_output

Disable fbcon text output (when switching to GUI compositor).

enable_output

Enable fbcon output. Called after boot completes (just before the shell launches) so that the hundreds of boot log lines don’t get rendered pixel-by-pixel to the framebuffer in QEMU.

flush

Blit all pending changes to the hardware framebuffer.

flush_row

Blit a single text row from back-buffer to MMIO and clear its dirty flag.

get_hw_info

Get the hardware framebuffer information.

init^⚠

Initialize the framebuffer console with the given parameters.

is_initialized

Check if the framebuffer console has been initialized.

mark_all_dirty_and_flush

Mark all rows dirty and trigger a full blit on the next flush.

update_cursor

Update the cursor overlay on the MMIO framebuffer.