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.
166 lines
5.8 KiB
Markdown
166 lines
5.8 KiB
Markdown
# emacs-gpu
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GNU Emacs with a GPU-accelerated display backend.
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On **macOS** it renders with **native Apple Metal**: text goes through a
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GPU glyph atlas, images and inline video are textures, and the whole
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frame is composited by the GPU instead of CoreGraphics. The output is
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pixel-accurate against the stock Cocoa backend.
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**OpenGL support for GNU/Linux and Windows is planned but not implemented
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yet.** The drawing logic is already platform-neutral (`src/gfxterm.c`)
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behind a small driver interface (`src/gfxdrv.h`); an OpenGL driver only
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needs to implement that interface (`src/glterm.c` is the documented
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skeleton). Contributions welcome.
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## Why a GPU backend?
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Beyond raw rendering, it enables things the stock backend cannot do:
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- **Inline video playback**: AVFoundation decodes straight into Metal
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textures (zero copies) and the frames are composited inside the
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buffer, following scrolling and clipped to the window. No xwidgets,
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no embedded browser.
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- **GPU cursor effects** (opt-in): expanding rings, comet trails and
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friends are drawn as a compositor overlay, without ever touching the
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buffer content underneath.
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- **A path to cheap visual effects**: buffer transitions, smooth
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scrolling or any future eye candy is one more shader pass over the
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composited frame, not a rewrite of the display engine.
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Text is rasterized once into a GPU glyph atlas and drawn as textured
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quads; scrolling moves already-rendered pixels with a texture blit.
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## Performance
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Measured on an Apple M1 Pro (Emacs 32 development build, 120x45 frame,
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font-locked `xdisp.c`, same binary with and without the GPU backend;
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`/usr/bin/time -l` over scripted workloads):
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| Workload | Stock (Cocoa) | GPU, vsync on (default) | GPU, vsync off |
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|---|---|---|---|
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| Sustained scroll, redisplays/s | 481 | 324 | 475 |
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| CPU for 15 s of that scroll | 16.0 s | **10.5 s** | 15.5 s |
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| Typing throughput (chars/s, machine-paced) | 108 | 52 | 106 |
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| Idle (8 s) CPU | 1.21 s | 1.19 s | same |
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| Peak RSS | ~140 MB | ~144 MB | same |
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Honest reading:
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- **Machine-paced throughput and CPU cost match the stock backend**
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(vsync off). There is no GPU tax.
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- With vsync on (the default), presents wait for the display refresh:
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the screen shows the same 60 fps either way, but Emacs burns ~35%
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less CPU under flat-out scrolling because it stops rendering frames
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nobody can see. Human-paced input is unaffected (the cap is ~52
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machine-paced updates/s; keyboard auto-repeat tops out well below
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that). `(gpu-vsync nil)` switches to uncapped, stock-like behavior.
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- Idle cost is identical and the GPU resources add ~4 MB of RSS.
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> Status: experimental, under active development.
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>
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> **Note:** I am not answering issues for now. Feel free to open them as
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> a public record (they will be read eventually), but do not expect a
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> reply at this stage.
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## Demos
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Inline video playing inside a buffer, decoded by AVFoundation straight
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into Metal textures (`gpu-video-insert`):
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An animated GIF playing next to font-locked code scrolling, all
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composited by the GPU:
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GPU cursor effects (`gpu-animations`), here the *sonicboom* mode:
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Buffer switches cross-fade on the GPU (on by default, configurable):
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## Installing
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With Homebrew (Apple Silicon, macOS 26+):
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```sh
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brew install --cask tanrax/tap/emacs-gpu
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```
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Or grab the signed, self-contained `Emacs.app` from the
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[releases](https://github.com/tanrax/emacs-gpu/releases).
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## Building on macOS
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Requires Xcode (or the Command Line Tools) and the usual Emacs build
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dependencies (`brew install autoconf automake gnutls texinfo pkg-config`).
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```sh
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./autogen.sh
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SDK=$(xcrun --sdk macosx --show-sdk-path)
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CC="xcrun clang" OBJC="xcrun clang" \
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CFLAGS="-isysroot $SDK" CPPFLAGS="-isysroot $SDK" OBJCFLAGS="-isysroot $SDK" \
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./configure --with-ns --with-mtl
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make -j$(sysctl -n hw.ncpu)
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```
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The binary is `src/emacs` (or install the app bundle from `nextstep/`).
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## Enabling the GPU backend
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The release app bundle enables it automatically (set the environment
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variable `EMACS_GPU_DISABLE=1` to start with the stock Cocoa backend
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instead). In a source build, switch a frame to Metal with:
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```elisp
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(add-to-list 'load-path "/path/to/emacs-gpu/lisp")
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(require 'gpu)
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(gpu-enable)
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```
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## Commands and options
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| Command | What it does |
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| `M-x gpu-status` | Show backend state: GPU device, animations, cursor mode |
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| `M-: (gpu-draw-stats)` | Renderer counters; `glyphs-drawn` growing proves the GPU is painting |
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| `M-x gpu-toggle-animations` | Toggle the GPU compositor overlay used by cursor effects |
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| `M-x gpu-set-cursor` | Pick the cursor effect: `block` (static, default, no effect), `sonicboom` (ring), `torpedo` (comet trail), `spring`, `ripple`, `pixiedust`, `hollow`, `beam` |
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| `M-: (gpu-vsync nil)` | Uncap presents from the display refresh (lower latency, more power) |
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| `M-: (gpu-video-insert "clip.mp4" 480 270 t)` | Play a video inline at point; follows scrolling |
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| `M-x gpu-video-stop` | Stop the inline video |
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Cursor effects trigger on cursor jumps (`M-<`, `M->`, isearch hits),
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not on single-character movement.
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Buffer switches cross-fade by default; tune or disable with:
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```elisp
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(setq gpu-buffer-transition-duration 0.15) ; seconds
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(setq gpu-buffer-transitions nil) ; turn it off
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```
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## How it works
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```
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redisplay engine (xdisp.c, untouched)
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↓
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src/gfxterm.c platform-neutral drawing policy
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↓
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src/gfxdrv.h driver interface (~25 ops)
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↓
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src/mtlterm.m Metal driver: glyph atlas (CoreText → R8 texture),
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render cycle on a persistent texture, AVFoundation
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video through CVMetalTextureCache
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```
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## License
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GNU General Public License v3 or later, same as GNU Emacs.
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