sway: restrict WLR_RENDERER workaround to kvm

pixman is known to not work at least on vmware, so we don't want to be
setting WLR_RENDERER indiscriminately.

sway/start-sway

@@ -10,14 +10,32 @@ export XDG_SESSION_TYPE=wayland
 
 ## Hardware compatibility
 # We can't be sure that the virtual GPU is compatible with Sway.
-if systemd-detect-virt --quiet --vm; then
-    # https://github.com/swaywm/sway/issues/6581
-    export WLR_NO_HARDWARE_CURSORS=1
-    # Fallback to the pixman renderer as it has a higher chance to work
-    # and will be faster than llvmpipe anyways.
-    # See https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/2871
-    export WLR_RENDERER=pixman
-fi
+# We should be attempting to detect an EGL driver instead, but that appears
+# to be a bit more complicated.
+case $(systemd-detect-virt --vm) in
+    "none"|"")
+        ;;
+    "kvm")
+        # https://github.com/swaywm/sway/issues/6581
+        export WLR_NO_HARDWARE_CURSORS=1
+        # There's two drivers we can get here, depending on the 3D acceleration
+        # flag state: either virtio_gpu/virgl or kms_swrast/llvmpipe.
+        #
+        # The former one causes graphical glitches in OpenGL apps when using
+        # 'pixman' renderer. The latter will crash 'gles2' renderer outright.
+        # Neither of those support 'vulkan'.
+        #
+        # The choice is obvious, at least until we learn to detect the driver
+        # instead of abusing the virtualization technology identifier.
+        #
+        # See also: https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/2871
+        export WLR_RENDERER=pixman
+        ;;
+    *)
+        # https://github.com/swaywm/sway/issues/6581
+        export WLR_NO_HARDWARE_CURSORS=1
+        ;;
+esac
 
 ## Load system environment customizations
 if [ -f /etc/sway/environment ]; then