feat(vk_native): opt-in Linux direct-scanout present path (ST-5539, #755)#756
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feat(vk_native): opt-in Linux direct-scanout present path (ST-5539, #755)#756dfattal wants to merge 1 commit into
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Reclaims the ~44% Xorg+gnome-shell presentation cost measured in ST-5539 by
acquiring the 3D-panel connector as a VkDisplayKHR (VK_EXT_acquire_xlib_display)
and scanning out to it directly, bypassing the desktop compositor.
Re-scope: on Linux the Leia plug-in weaves into a caller-provided target and
does NOT present (contract §3.3) — comp_vk_native owns the swapchain/present.
So this is a runtime-only change; no plug-in or srSDK change.
- comp_vk_native_window_direct.{c,h}: RandR output -> VkDisplayKHR -> acquire ->
display-plane surface (Monado comp_window_direct_randr model).
- Activate the dormant aux-layer VK_KHR_display helpers: VK_USE_PLATFORM_DISPLAY_KHR
and VK_USE_PLATFORM_XLIB_XRANDR_EXT were in xrt_config_vulkan.h.cmake_in but
never set() — new XRT_HAVE_XLIB_XRANDR (pkg x11+xrandr) drives them.
- null_compositor: request VK_KHR_display / direct_mode / acquire_xlib as OPTIONAL
instance exts -> graceful XCB fallback when absent.
- comp_vk_native_target: create_from_surface() consumes a pre-made (borrowed)
VkSurfaceKHR; external_surface guards teardown.
- compositor: fullscreen hosted path tries direct when DXR_LINUX_DIRECT_SCANOUT=1,
falls back silently to XCB on any failure; default path untouched.
Fullscreen-only (model-viewer, gauss). Compile-checked via Linux CI; needs
on-hardware validation on P1 + DS1 (Suki). Wayland/DRM-lease deferred.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Closes the presentation-overhead half of ST-5539 (sw-runtime-linux). Fixes #755.
What
Opt-in, fullscreen-only direct-scanout present path for the Linux Vulkan compositor: acquire the 3D-panel connector as a
VkDisplayKHR(VK_EXT_acquire_xlib_displayon Xorg) and scan out to it directly, bypassing Xorg + gnome-shell — the ~44% presentation cost Suki measured.Why it's runtime-only (re-scope from the report)
The report attributed the present to the Leia plug-in, but on Linux the plug-in weaves into a caller-provided target and does not own a swapchain or present (contract §3.3).
comp_vk_nativeowns the swapchain + present. No plug-in / srSDK change.Changes
comp_vk_native_window_direct.{c,h}— RandR output →VkDisplayKHR→ acquire → display-plane surface (Monadocomp_window_direct_randrmodel).VK_KHR_displaypath —VK_USE_PLATFORM_DISPLAY_KHR/_XLIB_XRANDR_EXTwere inxrt_config_vulkan.h.cmake_inbut neverset(); newXRT_HAVE_XLIB_XRANDR(pkgx11+xrandr) drives them. This is why the report saw "VK_KHR_display referenced but not wired."null_compositor— requests the display exts as optional → graceful XCB fallback.comp_vk_native_target—create_from_surface()consumes a pre-made (borrowed) surface;external_surfaceguards teardown.DXR_LINUX_DIRECT_SCANOUT=1, silently falls back to XCB on any failure. Default path untouched.Testing
libx11-dev+libxrandr-dev→XRT_HAVE_XLIB_XRANDRon).DXR_LINUX_DIRECT_SCANOUT=1+ a fullscreen app (model-viewer / gauss), confirm the connector is scanned out directly andintel_gpu_topshows the Xorg share drop.Notes
VK_EXT_acquire_drm_display) documented as the future path, not built here.🤖 Generated with Claude Code