backend: add preliminary support for driver detection

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/backend/driver.h

@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: MPL-2.0
+// Copyright (c) Yuxuan Shui <yshuiv7@gmail.com>
+
+#pragma once
+
+#include <stdio.h>
+#include <xcb/xcb.h>
+
+struct session;
+struct backend_base;
+
+/// A list of possible drivers.
+/// The driver situation is a bit complicated. There are two drivers we care about: the
+/// DDX, and the OpenGL driver. They are usually paired, but not always, since there is
+/// also the generic modesetting driver.
+/// This enum represents _both_ drivers.
+enum driver {
+	DRIVER_AMDGPU = 1, // AMDGPU for DDX, radeonsi for OpenGL
+	DRIVER_RADEON = 2, // ATI for DDX, mesa r600 for OpenGL
+	DRIVER_FGLRX = 4,
+	DRIVER_NVIDIA = 8,
+	DRIVER_NOUVEAU = 16,
+	DRIVER_INTEL = 32,
+	DRIVER_MODESETTING = 64,
+};
+
+/// Return a list of drivers currently in use by the X server.
+/// Note, this is a best-effort test, so no guarantee all drivers will be detected.
+enum driver detect_driver(xcb_connection_t *, struct backend_base *, xcb_window_t);
+
+// Print driver names to stdout, for diagnostics
+static inline void print_drivers(enum driver drivers) {
+	if (drivers & DRIVER_AMDGPU) {
+		printf("AMDGPU, ");
+	}
+	if (drivers & DRIVER_RADEON) {
+		printf("Radeon, ");
+	}
+	if (drivers & DRIVER_FGLRX) {
+		printf("fglrx, ");
+	}
+	if (drivers & DRIVER_NVIDIA) {
+		printf("NVIDIA, ");
+	}
+	if (drivers & DRIVER_NOUVEAU) {
+		printf("nouveau, ");
+	}
+	if (drivers & DRIVER_INTEL) {
+		printf("Intel, ");
+	}
+	if (drivers & DRIVER_MODESETTING) {
+		printf("modesetting, ");
+	}
+	printf("\b\b \n");
+}