Andros Fenollosa
b766212695
A redisplay pass runs several update cycles back-to-back (buffer window plus echo area), and with display sync every present blocked on a drawable: two blocking presents per keystroke halved typing throughput, and the present itself paid for a second command buffer. Presents now coalesce: one landing within ~8 ms of the previous commits to the static texture and is flushed by a one-shot main-queue block (or absorbed by the next cycle's present), and the composite pass is encoded on the same command buffer as the cycle's draws. The policy's flush presents through the same coalescing path. Benchmarks (M1 Pro, font-locked xdisp.c, 120x45): machine-paced typing goes from 30 to 106 chars/s and sustained scroll from 116 to 475 redisplays/s with vsync off, matching the stock backend's throughput and total CPU; with vsync on (default) the same visible 60 fps now costs ~35% less CPU than stock. README gains the numbers. Pixel parity, GIF/video playback, the first-tab-switch deferral and the echo-area tests are all unchanged. |
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| admin | ||
| build-aux | ||
| cross | ||
| doc | ||
| etc | ||
| exec | ||
| java | ||
| leim | ||
| lib | ||
| lib-src | ||
| lisp | ||
| lwlib | ||
| m4 | ||
| modules | ||
| msdos | ||
| nextstep | ||
| nt | ||
| oldXMenu | ||
| src | ||
| test | ||
| .clang-format | ||
| .clangd | ||
| .dir-locals.el | ||
| .gitattributes | ||
| .gitignore | ||
| .gitlab-ci.yml | ||
| .mailmap | ||
| autogen.sh | ||
| BUGS | ||
| ChangeLog.1 | ||
| ChangeLog.2 | ||
| ChangeLog.3 | ||
| ChangeLog.4 | ||
| ChangeLog.5 | ||
| ChangeLog.android | ||
| config.bat | ||
| configure.ac | ||
| CONTRIBUTE | ||
| COPYING | ||
| GNUmakefile | ||
| INSTALL | ||
| INSTALL.REPO | ||
| make-dist | ||
| Makefile.in | ||
| README | ||
| README.md | ||
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).
(mtl-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 (mtl-video-insert):
An animated GIF playing next to font-locked code scrolling, all composited by the GPU:
GPU cursor effects (mtl-animations), here the sonicboom mode:
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
Emacs starts with the regular Cocoa backend; switch a frame to Metal with:
(add-to-list 'load-path "/path/to/emacs-gpu/lisp")
(require 'mtl)
(mtl-enable)
Extras once enabled:
(mtl-video-insert "video.mp4" 480 270 t) ; inline video, follows scrolling
(mtl-animations t) ; GPU cursor effects (experimental)
(mtl-draw-stats) ; renderer counters
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.