The compositor recomposited and re-uploaded the entire screen on every pass of
its loop. At the 1280x720 the desktop actually boots into, gui_gfx_present()
memcpy'd 3.6 MB into the framebuffer per frame, and the background underneath
it was recomputed pixel by pixel every time.
Present only the damage
- Keep a RAM shadow of what the framebuffer currently holds and diff the back
buffer against it, pushing just the changed span of each row. Reading the
shadow costs a RAM access; the framebuffer write it avoids costs far more,
and the framebuffer is never read back.
- Each row is narrowed to its first and last differing pixel rather than
tracked as a set of runs: one memcpy per row keeps the loop tight, and a row
that changed in two distant places is rare enough that bridging the gap is
cheaper than the bookkeeping.
- gui_gfx_invalidate() forces a full push for when something outside the
compositor owns the screen, which the desktop calls on entry and on exit
around the framebuffer console.
Cache the wallpaper
- The vertical gradient, the blended grid and the branding text never change
between frames, so they are painted once into a cached buffer and blitted
back per frame. The cache is keyed on resolution and the grid setting, so
toggling the grid from the context menu still repaints it.
No drawing code changed: the damage is derived from the frame itself, so every
widget, window and app keeps rendering exactly as before.
Measured in QEMU at 1280x720: an idle desktop with two windows open went from
921600 pixels per frame to 3609, about 0.4% of a full blit. A screendump of
the running desktop is unchanged -- wallpaper, grid, icons, both windows,
taskbar and cursor all render identically.
Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_0161Jh7uCEMLYEMNPsjC1LKf
- Upgrade resolution to 800x600 @ 32bpp TrueColor with Bochs/QEMU VBE LFB
- Implement full 8042 Aux PS/2 mouse controller driver on IRQ 12 (vector 44) with packet decode and bounds clamping
- Add high-definition 8x16 font rasterizer with text drop shadows for sharp typography
- Upgrade to smooth 16x24 anti-aliased cursor with dark slate outline and drop shadow
- Increase titlebars to 24px and taskbar to 32px with modern desktop styling
- Re-architect applications (SysMon, Terminal, Explorer, Calc, Paint, About) for spacious high-res display
- Create separate feature branch 'feat/gui-desktop'
- Implement double-buffered 2D graphics engine with alpha blending, gradients, rounded rects, and font rasterization in gui/gui_gfx.c and include/gui/gui_gfx.h
- Implement alpha-blended mouse pointer overlay in gui/gui_cursor.c and include/gui/gui_cursor.h
- Implement SUB-WM Window Manager with draggable titlebars, close/minimize buttons, drop shadows, and event routing in gui/gui_wm.c and include/gui/gui_wm.h
- Implement Cyberpunk/Nord desktop environment with wallpaper, taskbar, start menu popup, and system tray in gui/gui_desktop.c and include/gui/gui_desktop.h
- Implement built-in GUI apps: System Performance Monitor, GUI Terminal Emulator, File Explorer, Calculator, Paint Studio, and About dialog in gui/gui_apps.c and include/gui/gui_apps.h
- Add 'startx', 'gui', and 'desktop' applets in LazyBox suite
- Verified multi-architecture compilation across x86_64, AArch64, and ARMv8i
