andros
6f8f953c0c
The gpu-cursor-animation defcustom used :set #'set-default, so changing the cursor mode at runtime (via gpu-set-cursor / setopt) only updated the Lisp variable and never reached the live Metal driver. Wire :set to call gpu-cursor-mode so the change propagates immediately. Also set the default cursor to 'block (static, no effect); cursor effects are now opt-in via gpu-set-cursor. Bump version to 0.1.1.
5.8 KiB
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):
Installing
With Homebrew (Apple Silicon, macOS 26+):
brew install --cask tanrax/tap/emacs-gpu
Or grab the signed, self-contained Emacs.app from the
releases.
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 the GPU compositor overlay used by cursor effects |
M-x gpu-set-cursor |
Pick the cursor effect: block (static, default, no effect), sonicboom (ring), torpedo (comet trail), spring, ripple, pixiedust, hollow, beam |
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.