emacs-gpu

GNU Emacs with a GPU-accelerated display backend.

On macOS it renders with native Apple Metal: text goes through a GPU glyph atlas, images and inline video are textures, and the whole frame is composited by the GPU instead of CoreGraphics. The output is pixel-accurate against the stock Cocoa backend.

OpenGL support for GNU/Linux and Windows is planned but not implemented yet. The drawing logic is already platform-neutral (src/gfxterm.c) behind a small driver interface (src/gfxdrv.h); an OpenGL driver only needs to implement that interface (src/glterm.c is the documented skeleton). Contributions welcome.

Why a GPU backend?

Beyond raw rendering, it enables things the stock backend cannot do:

• Inline video playback: AVFoundation decodes straight into Metal textures (zero copies) and the frames are composited inside the buffer, following scrolling and clipped to the window. No xwidgets, no embedded browser.
• GPU cursor effects (opt-in): expanding rings, comet trails and friends are drawn as a compositor overlay, without ever touching the buffer content underneath.
• A path to cheap visual effects: buffer transitions, smooth scrolling or any future eye candy is one more shader pass over the composited frame, not a rewrite of the display engine.

Text is rasterized once into a GPU glyph atlas and drawn as textured quads; scrolling moves already-rendered pixels with a texture blit.

Performance

Measured on an Apple M1 Pro (Emacs 32 development build, 120x45 frame, font-locked xdisp.c, same binary with and without the GPU backend; /usr/bin/time -l over scripted workloads):

Workload	Stock (Cocoa)	GPU, vsync on (default)	GPU, vsync off
Sustained scroll, redisplays/s	481	324	475
CPU for 15 s of that scroll	16.0 s	10.5 s	15.5 s
Typing throughput (chars/s, machine-paced)	108	52	106
Idle (8 s) CPU	1.21 s	1.19 s	same
Peak RSS	~140 MB	~144 MB	same

Honest reading:

• Machine-paced throughput and CPU cost match the stock backend (vsync off). There is no GPU tax.
• With vsync on (the default), presents wait for the display refresh: the screen shows the same 60 fps either way, but Emacs burns ~35% less CPU under flat-out scrolling because it stops rendering frames nobody can see. Human-paced input is unaffected (the cap is ~52 machine-paced updates/s; keyboard auto-repeat tops out well below that). (gpu-vsync nil) switches to uncapped, stock-like behavior.
• Idle cost is identical and the GPU resources add ~4 MB of RSS.

Status: experimental, under active development.

Note: I am not answering issues for now. Feel free to open them as a public record (they will be read eventually), but do not expect a reply at this stage.

Demos

Inline video playing inside a buffer, decoded by AVFoundation straight into Metal textures (gpu-video-insert):

An animated GIF playing next to font-locked code scrolling, all composited by the GPU:

GPU cursor effects (gpu-animations), here the sonicboom mode:

Buffer switches cross-fade on the GPU (on by default, configurable):

Building on macOS

Requires Xcode (or the Command Line Tools) and the usual Emacs build dependencies (brew install autoconf automake gnutls texinfo pkg-config).

./autogen.sh

SDK=$(xcrun --sdk macosx --show-sdk-path)
CC="xcrun clang" OBJC="xcrun clang" \
CFLAGS="-isysroot $SDK" CPPFLAGS="-isysroot $SDK" OBJCFLAGS="-isysroot $SDK" \
./configure --with-ns --with-mtl

make -j$(sysctl -n hw.ncpu)

The binary is src/emacs (or install the app bundle from nextstep/).

Enabling the GPU backend

The release app bundle enables it automatically (set the environment variable EMACS_GPU_DISABLE=1 to start with the stock Cocoa backend instead). In a source build, switch a frame to Metal with:

(add-to-list 'load-path "/path/to/emacs-gpu/lisp")
(require 'gpu)
(gpu-enable)

Commands and options

Command	What it does
M-x gpu-status	Show backend state: GPU device, animations, cursor mode
M-: (gpu-draw-stats)	Renderer counters; glyphs-drawn growing proves the GPU is painting
M-x gpu-toggle-animations	Toggle GPU cursor effects (on by default)
M-x gpu-set-cursor	Pick the cursor effect: sonicboom (default), torpedo (comet trail), spring, ripple, pixiedust, hollow, beam, block
M-: (gpu-vsync nil)	Uncap presents from the display refresh (lower latency, more power)
M-: (gpu-video-insert "clip.mp4" 480 270 t)	Play a video inline at point; follows scrolling
M-x gpu-video-stop	Stop the inline video

Cursor effects trigger on cursor jumps (M-<, M->, isearch hits), not on single-character movement.

Buffer switches cross-fade by default; tune or disable with:

(setq gpu-buffer-transition-duration 0.15) ; seconds
(setq gpu-buffer-transitions nil)          ; turn it off

How it works

redisplay engine (xdisp.c, untouched)
        ↓
src/gfxterm.c   platform-neutral drawing policy
        ↓
src/gfxdrv.h    driver interface (~25 ops)
        ↓
src/mtlterm.m   Metal driver: glyph atlas (CoreText → R8 texture),
                render cycle on a persistent texture, AVFoundation
                video through CVMetalTextureCache

License

GNU General Public License v3 or later, same as GNU Emacs.