offscreen_gl.hpp

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// SPDX-FileCopyrightText: 2026 Povl Filip Sonne-Frederiksen
//
// SPDX-License-Identifier: GPL-3.0-or-later
 
#pragma once
 
// Can this machine create an offscreen OpenGL context? (#313)
//
// VTK's headless path ends in vtkEGLRenderWindow, and on a machine where EGL
// has nothing to render on — a GitHub-hosted CI runner, a nix build sandbox —
// that render window crashes on its first Render() instead of reporting the
// failure. Everything downstream of it (the SupportsOpenGL() guard in
// render_view(), the "blank frame" check, the caller's try/catch) is therefore
// unreachable, and STANDARDS §5 is served by a segfault.
//
// This header answers the question *before* any VTK object is touched, and it
// answers it by asking EGL rather than by looking at the filesystem. That
// distinction is the whole point: the obvious probe — "is there a
// /dev/dri/renderD* node?" — reports failure on two configurations that render
// perfectly well.
//
//   - A software rasteriser (Mesa llvmpipe) has no DRM node at all. It still
//     exposes an EGL device, and EGL still initialises on it.
//   - A remote or containerised GPU can be reachable through a vendor EGL
//     driver with no local render node bind-mounted.
//
// Asking EGL to enumerate its devices and initialise one covers both, and
// fails only when there is genuinely nothing to render on.
 
#include <string>
 
namespace reusex::visualize {

enum class OffscreenGlStatus {
  usable,
  unusable,
  unknown,
};

struct OffscreenGlProbe {
  OffscreenGlStatus status = OffscreenGlStatus::unknown;
  std::string detail;
  int devices = -1;
};

OffscreenGlProbe probe_offscreen_gl() noexcept;

bool display_configured() noexcept;
 
} // namespace reusex::visualize