Pick a renderer from the GPU and fall back to software rendering

bin/blob-hw-gpu-accelerated

@@ -0,0 +1,28 @@
+#!/bin/bash
+
+# blob:summary=Detect whether a DRM device with an accelerated driver is present.
+
+drm_path="${BLOB_DRM_PATH:-/sys/class/drm}"
+
+accelerated_drivers=(
+  amdgpu
+  i915
+  nouveau
+  nvidia
+  nvidia-drm
+  radeon
+  xe
+)
+
+shopt -s nullglob
+
+for card in "$drm_path"/card[0-9]*; do
+  [[ -L $card/device/driver ]] || continue
+  driver=$(basename "$(readlink -f "$card/device/driver")")
+
+  for accelerated in "${accelerated_drivers[@]}"; do
+    [[ $driver == "$accelerated" ]] && exit 0
+  done
+done
+
+exit 1

default/hypr/envs.lua

@@ -37,6 +37,7 @@ hl.env("PATH", table.concat(kept, ":"))
 
 -- Hardware-specific environment.
 require("default.hypr.nvidia")
+require("default.hypr.renderer")
 
 hl.config({
   xwayland = {

default/hypr/renderer.lua

@@ -0,0 +1,14 @@
+local paths = require("default.hypr.paths")
+
+local accelerated = paths.blob_path .. "/bin/blob-hw-gpu-accelerated"
+
+if not o.shell_succeeds(o.shell_quote(accelerated)) then
+  hl.env("LIBGL_ALWAYS_SOFTWARE", "1")
+  hl.env("WLR_NO_HARDWARE_CURSORS", "1")
+
+  hl.config({
+    cursor = {
+      no_hardware_cursors = true,
+    },
+  })
+end

default/sddm/hyprland-greeter.lua

@@ -1,6 +1,31 @@
 -- Hyprland config for the SDDM Wayland greeter. SDDM starts the greeter itself
 -- once the compositor is up, so nothing here launches anything.
+-- The greeter runs as SDDM's own user, with no BLOB_PATH and no read access to
+-- the checkout, so it calls the copy install.sh puts in /usr/local/bin rather
+-- than loading the Lua modules the session uses. A detector that is not there
+-- yet reads as no acceleration, which is the fallback that always draws.
+local function gpu_is_accelerated()
+  local pipe = io.popen("/usr/local/bin/blob-hw-gpu-accelerated >/dev/null 2>&1 && echo OK")
+  if not pipe then
+    return false
+  end
+
+  local output = pipe:read("*a") or ""
+  pipe:close()
+
+  return output:match("OK") ~= nil
+end
+
+if not gpu_is_accelerated() then
+  hl.env("LIBGL_ALWAYS_SOFTWARE", "1")
+  hl.env("WLR_NO_HARDWARE_CURSORS", "1")
+end
+
 hl.config({
+  cursor = {
+    no_hardware_cursors = true,
+  },
+
   misc = {
     disable_hyprland_logo = true,
     disable_splash_rendering = true,

docs/commands.md

@@ -206,6 +206,7 @@ of the `blob` listing.
 | `blob-hw-display` | Print the most likely display backlight device. | - |
 | `blob-hw-external` | Returns true when an external monitor is physically connected. | - |
 | `blob-hw-fingerprint` | Returns true when a fingerprint reader is present (hidden) | - |
+| `blob-hw-gpu-accelerated` | Detect whether a DRM device with an accelerated driver is present. | - |
 | `blob-hw-hybrid-gpu` | Detect whether the system has an active hybrid GPU configuration | - |
 | `blob-hw-laptop` | Returns true when running on a laptop (has a lid or laptop chassis). | - |
 | `blob-hw-laptop-closed` | Returns true when the laptop lid is closed (hidden) | - |

docs/install.md

@@ -86,10 +86,14 @@ with `--check`.
    | `/usr/local/share/wayland-sessions/blob.desktop` | the session SDDM offers |
    | `/etc/sddm.conf.d/zz-blob.conf` | Wayland greeter, run on Hyprland, stock theme, remember the last session |
    | `/etc/sddm/hyprland-greeter.lua` | the greeter's own tiny Hyprland config |
+   | `/usr/local/bin/blob-hw-gpu-accelerated` | the renderer check that config runs, where SDDM's user can read it |
 
    The greeter config matters more than it looks: SDDM's stock Wayland greeter
    runs on `weston`, which Blob does not install, so a default SDDM would fail
-   to draw anything. That greeter config has to be Lua: Hyprland dropped the old
+   to draw anything. The installer checks that the `CompositorCommand` named in
+   `zz-blob.conf` is actually installed and warns when it is not, because SDDM
+   with a compositor command it cannot run starts, fails, and leaves the machine
+   sitting at a text console with no explanation. That greeter config has to be Lua: Hyprland dropped the old
    hyprlang format, and a config it cannot parse leaves the greeter with no
    compositor and the screen black. `sddm.service` is enabled and the default
    systemd target is set to `graphical.target`, which an Arch install without a
@@ -131,6 +135,52 @@ with `--check`.
 | `--autologin` | skip the SDDM prompt for this user |
 | `--no-launch` | leave the login screen for the next reboot |
 
+## Choosing a renderer
+
+Hyprland renders through Mesa, and on an adapter Mesa has no driver for it exits
+with `failed to create dri2 screen` instead of drawing. The greeter is Hyprland
+too, so that is a black screen at boot and a second one after login, which is
+how a machine with no real GPU behind its display arrives.
+
+`blob-hw-gpu-accelerated` decides which way to go. It reads the kernel driver of
+each `/sys/class/drm/card*` from sysfs, not from `lspci`, which reads PCI config
+space and resumes runtime-suspended GPUs. A card driven by `amdgpu`, `i915`,
+`nouveau`, `nvidia`, `nvidia-drm`, `radeon` or `xe` is a real integrated or
+dedicated GPU and hardware rendering is left alone. Everything else - `vmwgfx`,
+`vboxvideo`, `qxl`, `bochs-drm`, `cirrus`, `simpledrm`, `vkms`, `virtio_gpu` -
+is virtual or framebuffer-only, and two settings are applied:
+
+| Setting | Effect |
+| --- | --- |
+| `LIBGL_ALWAYS_SOFTWARE=1` | Mesa uses llvmpipe, which renders on the CPU |
+| `WLR_NO_HARDWARE_CURSORS=1`, `cursor:no_hardware_cursors` | the cursor is drawn by the compositor, since there is no plane to put it on |
+
+llvmpipe is slow and it draws. A machine with a real GPU never touches it.
+
+Two places read the detector, because they run as different users:
+
+| Where | How |
+| --- | --- |
+| the session | `default/hypr/renderer.lua`, required from `envs.lua` beside `nvidia.lua`, through `$BLOB_PATH/bin` |
+| the greeter | `default/sddm/hyprland-greeter.lua`, through `/usr/local/bin/blob-hw-gpu-accelerated` |
+
+The greeter runs as SDDM's own user, with no `BLOB_PATH` and no read access to
+your home directory, so `install.sh` copies the detector to `/usr/local/bin`.
+A detector that is not there yet reads as no acceleration, which is the fallback
+that always draws.
+
+To add a driver to the accelerated list, edit `accelerated_drivers` in
+`bin/blob-hw-gpu-accelerated` and rerun `./install.sh` so the greeter's copy
+follows. `virtio_gpu` is deliberately not on it: QEMU only accelerates it when
+the host enables virgl, and Mesa fails the same way when it does not.
+
+To see the difference by hand, from a console:
+
+```bash
+Hyprland                          # fails with the dri2 error
+LIBGL_ALWAYS_SOFTWARE=1 Hyprland  # starts
+```
+
 ## Uninstall
 
 `./uninstall.sh` removes the config, the user units, the `/etc` drop-ins, the

install.sh

@@ -81,6 +81,7 @@ install_login_config
 install_session_entry
 install_autologin
 enable_display_manager
+report_greeter_compositor
 report_login_conflicts
 report_desktop_essentials
 

install/steps/login.sh

@@ -8,6 +8,7 @@ greeter_compositor_config=/etc/sddm/hyprland-greeter.lua
 # ISO, or a previous desktop left behind.
 blob_greeter_conf="$greeter_config_dir/zz-blob.conf"
 blob_autologin_conf="$greeter_config_dir/zzz-blob-autologin.conf"
+greeter_gpu_detector=/usr/local/bin/blob-hw-gpu-accelerated
 
 # SDDM's stock Wayland greeter runs on weston, which Blob does not install.
 # Point it at Hyprland with a greeter-only config instead. That config is Lua:
@@ -18,6 +19,8 @@ install_login_config() {
     "$greeter_compositor_config" "sddm/hyprland-greeter.lua"
   install_root_file "$repo_dir/default/sddm/zz-blob.conf" \
     "$blob_greeter_conf" "sddm.conf.d/zz-blob.conf"
+  install_root_file "$repo_dir/bin/blob-hw-gpu-accelerated" \
+    "$greeter_gpu_detector" "blob-hw-gpu-accelerated" 0755
 }
 
 install_session_entry() {
@@ -54,6 +57,22 @@ setting_value() {
   sed -n "s/^[[:space:]]*$key[[:space:]]*=[[:space:]]*//p" "$file" | tail -1
 }
 
+# SDDM runs CompositorCommand to get a Wayland greeter on screen. When that
+# binary is not installed SDDM fails with no greeter at all, which reads as a
+# machine that boots to a console for no reason, so name it here instead.
+report_greeter_compositor() {
+  local command_line binary
+
+  command_line="$(setting_value "$repo_dir/default/sddm/zz-blob.conf" CompositorCommand)"
+  binary="${command_line%% *}"
+
+  [[ -n $binary ]] || return 0
+  command -v "$binary" &>/dev/null && return 0
+
+  say "WARN  the greeter's compositor command '$binary' is not installed"
+  say "      SDDM cannot draw a greeter without it; it is set in $blob_greeter_conf"
+}
+
 # zz-blob.conf blanks Theme and Autologin, so a leftover drop-in cannot point the
 # greeter at a theme that was uninstalled or autolog into a session that no
 # longer exists. Either one leaves SDDM on a black screen it never falls back

packages/blob.packages

@@ -6,6 +6,7 @@
 
 # Compositor and shell
 hyprland
+mesa
 quickshell
 uwsm
 sddm

uninstall.sh

@@ -8,6 +8,7 @@ session_entry="/usr/local/share/wayland-sessions/blob.desktop"
 
 root_files=(
   /etc/profile.d/blob.sh
+  /usr/local/bin/blob-hw-gpu-accelerated
   /etc/sddm.conf.d/zz-blob.conf
   /etc/sddm.conf.d/zzz-blob-autologin.conf
   /etc/sddm/hyprland-greeter.conf