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William Theesfeld edited this page Apr 15, 2026 · 1 revision

Architecture

Overview

┌─────────────────────────────────────────────┐
│             VGP Server (vgp)                │
│                                             │
│  ┌─────────┐ ┌──────────┐ ┌─────────────┐  │
│  │ DRM/KMS │ │ NanoVG   │ │ Compositor  │  │
│  │ + GBM   │ │ GLES 3.0 │ │ + Tiling    │  │
│  └────┬────┘ └────┬─────┘ └──────┬──────┘  │
│       │           │              │          │
│  ┌────┴───┐  ┌────┴──────┐  ┌───┴──────┐  │
│  │libinput│  │ Shader Mgr│  │ IPC      │  │
│  │+ xkb   │  │ + Themes  │  │ Server   │  │
│  └────────┘  └───────────┘  └──────────┘  │
│                                             │
│  ┌─────────┐ ┌────────┐ ┌──────────────┐  │
│  │libseat  │ │ D-Bus  │ │ Lock Screen  │  │
│  │Session  │ │Notify  │ │ + Animations │  │
│  └─────────┘ └────────┘ └──────────────┘  │
└──────────────────┬──────────────────────────┘
                   │ Unix domain socket
    ┌──────────────┼──────────────┐
    │              │              │
 vgp-term    vgp-settings   vgp-files

Rendering Pipeline

  1. DRM/KMS: Opens GPU via libseat, creates GBM surfaces per output
  2. EGL: Creates OpenGL ES 3.0 context on GBM surfaces
  3. NanoVG: Tessellates vector paths into GPU triangles
  4. Shaders: Custom GLSL fragment shaders for backgrounds, rendered before NanoVG frame
  5. Compositing: NanoVG draws decorations, text, UI elements as vector paths
  6. Scanout: eglSwapBuffers → GBM BO → drmModeSetCrtc/PageFlip

Cell Grid Protocol

Terminals don't render pixels. They send a cell grid:

typedef struct vgp_cell {
    uint32_t codepoint;   // Unicode character
    uint8_t  fg_r, fg_g, fg_b;
    uint8_t  bg_r, bg_g, bg_b;
    uint8_t  attrs;       // bold, italic, underline, etc.
    uint8_t  width;       // cell width (1 or 2 for wide chars)
} vgp_cell_t;             // 12 bytes per cell

An 80x24 terminal sends 23,040 bytes per frame (vs 1,600,000 bytes for pixel data). The server renders each character with NanoVG at native output resolution.

Key Source Files

File Purpose
src/server/main.c Entry point, signal handling
src/server/server.c Server state, init, event dispatch
src/server/drm.c DRM/KMS, output enumeration, page flips
src/server/backend_gpu.c NanoVG/EGL/GBM GPU backend
src/server/renderer.c Frame rendering, decoration, cell grid
src/server/compositor.c Window management, z-order, focus
src/server/tiling.c Tiling layout algorithms
src/server/ipc.c Unix socket IPC server
src/server/config.c TOML config parser
src/server/shader_loader.c GLSL shader compilation
src/server/lockscreen.c Lock screen
src/libvgp/vgp.c Client library
src/libvgp-ui/vgp-ui.c Cell grid UI toolkit
src/vgp-term/term.c Terminal emulator

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