OpenGL

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; CUDA compute is on Execution-Frontier.md. Canonical sources: ../docs/04-implementation/05-graphics-execution-plan.md (the plan and milestones), ../docs/04-implementation/04-real-render-walls.md (the measured walls) and ../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:

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