Log the Metal GPU and create a Vulkan device only for it

On a hybrid laptop (issue #3) Indium took whichever Vulkan device the
loader listed first, usually the integrated GPU, and still created a
VkDevice on every other supported GPU, waking a discrete GPU it never
used. Drawables reach the presenting OpenGL context as opaque FDs, which
only work on one physical device, and nothing checked that.

Indium now appends the device list, the selected device and the reason
to guest /tmp/metal-device.log, and creates a VkDevice for the selected
device only (/tmp/metal-all-devices restores the old behaviour).
/tmp/metal-gpu or METAL_INDIUM_GPU selects a device by index or name
for diagnosis. QuartzCore logs the presenting GL renderer and compares
its device UUID with the Vulkan device's (match=yes / MISMATCH); it
queries Vulkan itself, so it needs no new libindium export.

On the RX 6600 desktop the game selected RADV, created 1 VkDevice of 2
supported (lavapipe no longer gets one) and logged match=yes in a match.
Running on NVIDIA through prime-run is documented but not validated.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/TROUBLESHOOTING.md

@@ -156,6 +156,39 @@ Compare matches on the same map: Bilgewater runs a few percent below Hexgate.
 
 On Hyprland, also check that direct scanout is off (`hyprctl getoption render:direct_scanout` prints `int: 0`). The first match with it off ran about 16 FPS faster than the previous one on the same build; see the next section.
 
+## Hybrid graphics laptops (AMD/Intel iGPU + NVIDIA)
+
+Metal renders with Vulkan, and each finished frame is handed to an OpenGL (EGL) context that presents it. The hand-off uses opaque file descriptors, which only work when Vulkan and OpenGL run on the same GPU. Indium takes the first Vulkan device the loader lists, and on a hybrid laptop both that device and the EGL context are normally the integrated GPU, so the discrete GPU stays idle. A report in [issue #3](https://github.com/lucannez64/darling-lol/issues/3) (Ryzen 9 5900HS, RTX 3060 Laptop) measured about 70 FPS in ARAM; which GPU rendered that match is not known. **Running on an NVIDIA GPU is not validated.**
+
+### Run on the discrete GPU
+
+Start the launcher with PRIME render offload so that both Vulkan and OpenGL move to the NVIDIA GPU:
+
+```sh
+prime-run sh scripts/run.sh
+```
+
+`prime-run` sets `__NV_PRIME_RENDER_OFFLOAD=1`, `__VK_LAYER_NV_optimus=NVIDIA_only` and `__GLX_VENDOR_LIBRARY_NAME=nvidia`. `darling` copies the caller's environment into the guest, and guest processes inherit it; whether the Riot client passes all of it to the game has not been checked; the log below shows the result. Darling's OpenGL uses EGL, so if the log below still shows the integrated GPU as the presenting renderer, also set `__EGL_VENDOR_LIBRARY_FILENAMES=/usr/share/glvnd/egl_vendor.d/10_nvidia.json`. On two Mesa GPUs, `DRI_PRIME=1` does the same.
+
+The guest file `/tmp/metal-gpu` (a device index or part of its name, for example `nvidia`) moves only the Vulkan side. Use it for diagnosis: on its own it splits the two sides across GPUs, and frames cannot be presented.
+
+### Check which GPU rendered
+
+Each process that uses Metal appends to guest `/tmp/metal-device.log` (host `~/.darling/private/tmp/metal-device.log`): every Vulkan device the loader reported, the selected one and why, and the renderer of the presenting OpenGL context with both device UUIDs:
+
+```
+[MetalDevice] pid=… physical name="NVIDIA GeForce RTX 3060 Laptop GPU" type=discrete vendorID=0x10de … supported=yes
+[MetalDevice] pid=… selected name="NVIDIA GeForce RTX 3060 Laptop GPU" type=discrete … reason=loader-first
+[MetalDevice] pid=… created VkDevice for 1 of 1 supported device(s) (selected only)
+[MetalDevice] pid=… presenting GL renderer="…" vendor="NVIDIA Corporation" … match=yes
+```
+
+`MISMATCH` on the presenting line means Vulkan and OpenGL are on different GPUs. `match=unknown` means the OpenGL driver reports no device UUID. Include this file with performance reports.
+
+### Host-side checks
+
+These are host settings, not game settings. Run on AC power, and use a performance power profile (`powerprofilesctl set performance`, or `asusctl profile -P Performance` on ASUS laptops). On the tested desktop the game is limited mostly by its own main thread on the CPU, not by the GPU (see [status](STATUS.md#game-fps-2026-10-1314)), so laptop CPU power limits matter as much as the GPU choice.
+
 ## Cursor stops changing shape in fullscreen
 
 On Hyprland the game's cursor can keep its first shape (for example, it never switches to the attack cursor) until you leave and re-enter fullscreen. Darling sends every change to the X server; what freezes the shape on screen is Hyprland's direct scanout of the fullscreen Xwayland window. Turn it off in `hyprland.conf`: