# OpenGL

> **Scope.** How a stock guest OpenGL application's commands travel through the
> unmodified NVIDIA stack on the emulated vGPU, and the honest state of running
> OpenGL on it. The host-side execution machinery shared by all graphics APIs
> is on [`Graphics-Execution.md`](Graphics-Execution.md); CUDA compute is on
> [`Execution-Frontier.md`](Execution-Frontier.md). Canonical sources:
> [`../docs/04-implementation/05-graphics-execution-plan.md`](../docs/04-implementation/05-graphics-execution-plan.md)
> (the plan and milestones),
> [`../docs/04-implementation/04-real-render-walls.md`](../docs/04-implementation/04-real-render-walls.md)
> (the measured walls) and
> [`../docs/03-architecture/02-guest-stack-and-cudasw.md`](../docs/03-architecture/02-guest-stack-and-cudasw.md)
> (the guest stack). The docs tree wins on disagreement.

Status: 2026-10-30, tree `master @ b4930168`. Tags: `[live]` observed with the
stock guest driver; `[wip]` partial; `[wall]` current blocker; `[target]`
defined success state.

## 1. The guest OpenGL stack

On Linux, an OpenGL application does not talk to the kernel driver directly:
it talks to the GL implementation, and — when a display is involved — through
the X server's GLX extension:

```text
application (toolkit / SDL / GLFW / raw GLX)
  -> libGL (dispatch)                    -> libGLX_nvidia (NVIDIA GLX client)
  -> libnvidia-glcore (the vendor GL engine: state, programs, shaders, draws)
  -> ioctls + mappings to nvidia.ko      -> channels, buffers, synchronization
X server (Xorg)
  -> GLX extension module (glxserver_nvidia) and the NVIDIA DDX (X driver)
  -> owns the screen, drawables and the present path
```

Two forms of operation exist, and both are visible in the guest:

* **Direct rendering** — the normal desktop case. The GL client builds GPU
  commands in its own process and the X server coordinates buffers and
  presents. The client's channel is the source of truth for per-draw state.
* **Indirect GLX** — the client's GL protocol is serialised to the X server,
  which executes it against its own GL context. Here the X server's channel
  carries the graphics stream.

On the emulated vGPU the readable command source today is the **X server's
channel**, whose graphics-class (`0xC597`, `TURING_A`) sections the emulation
captures and executes ([`Graphics-Execution.md`](Graphics-Execution.md) §3).

## 2. What an NVIDIA GL frame involves (observed shapes)

* **Context and state setup** — shader programs (SASS) uploaded to device
  memory, constant/descriptor banks, render targets and depth surfaces
  allocated and mapped.
* **Per-draw work** — a graphics-class method stream: state binds (viewport,
  render target, ZS, blend/ROP), program and constant binds, vertex/index
  data, and draw-issuing methods that drive the fixed-function pipeline
  (vertex fetch, primitive assembly, rasterisation, fragment work, ROP).
* **Program/descriptor delivery** — the driver uploads shader code and
  descriptors through its copy/utility-channel inline-data path; this upload
  is the piece the emulation must materialise for the engine to run *real*
  programs ([`Vulkan.md`](Vulkan.md) has the mirror-image of the same gap).
* **Present** — the X server's present/readback path runs as light 2D-class
  and copy-engine operations; the emulator decodes and executes those shapes.

## 3. Status on the emulated vGPU

Rated honestly, against the milestone ladder in the plan:

| Item | State |
|---|---|
| X server initialises on the emulated vGPU (driver push-DMA sanity test, ScreenInit) | `[live]` |
| `glxinfo -B` reports the NVIDIA renderer (OpenGL 4.6.0, driver 570.144) | `[live]` |
| The X driver's RC-watchdog channel registers and its notifier is authored | `[live]` |
| GZDoom launches and runs on the emulated vGPU | `[live]` (menu/frames black) |
| X server's `0xC597` graphics section captured and decoded | `[live]` |
| Engine executes a launch built from the captured section (real `sm_75` SASS retired) | `[live]` |
| Verbatim 3D method-stream replay retired by the engine, no MMU fault | `[live]` |
| Direct GL client: device-init gate handled; client channels allocate; readback path returns with no GL error | `[wip]` |
| Direct GL client submits its per-frame draws | `[wall]` (no submissions observed) |
| Non-black rendered frames through the emulated vGPU | `[wall]` |
| 60 fps sustained, no forcing (M-GL4) | `[target]` |

## 4. How OpenGL runs are verified

Instruments that matter, in order of usefulness: the X server log and
`xdpyinfo` (did the server initialise?), `glxinfo -B` (which renderer is
real), the application's own progress output, and frame capture at the GL
source (a swap-hook capture is the ground truth for pixels — the X screen
itself is not, on some stacks). Captures are decoded offline and scored:
fraction of pixels above a luminance threshold, colour count, and
frame-to-frame motion. A run counts only when the capture shows motion with
the NVIDIA renderer in use.

## 5. Milestones on this path

The graphics plan defines M-GL1 (client context-init decodes and executes; the
client leaves its retry loop), M-GL2 (`glxgears` non-black), M-GL3 (GZDoom GL
non-black through the mdev), M-GL4 (60 fps, no forcing), M-GL5 (two VMs, two
mdevs), M-GL6 (split-screen video). The project sits **between M-GL1 and
M-GL2**: the interface work is done — the client creates its channels and its
readback path is clean — and pixels are the gate.

## 6. What is not claimed

* No OpenGL frame from the emulated vGPU has produced real rendered pixels
  yet; every capture so far is black.
* No frame-rate or latency numbers.
* The published two-VM GZDoom demo videos used the labelled `virtio-gpu`/
  `virgl` path, not the emulated vGPU.

## 7. Related pages

* [`Graphics-Execution.md`](Graphics-Execution.md) — the shared execution
  machinery and the ranked walls.
* [`Vulkan.md`](Vulkan.md) — the sibling API path, further along in the
  pipeline lifecycle.
* [`DirectX.md`](DirectX.md) — the Windows/DirectX target.
* [`CUDA-Userspace-Driver.md`](CUDA-Userspace-Driver.md) — how the NVIDIA
  userspace stack is analysed.
* [`Install-and-First-Run.md`](Install-and-First-Run.md) — bringing the stack
  up.
* [`../docs/04-implementation/05-graphics-execution-plan.md`](../docs/04-implementation/05-graphics-execution-plan.md) —
  the canonical plan, gap list and gates.