screencast: create gbm device

This is done by using the first device returned by getDRMDevices2
containing a render node (DRM_NODE_RENDER).

include/screencast_common.h

@@ -1,6 +1,7 @@
 #ifndef SCREENCAST_COMMON_H
 #define SCREENCAST_COMMON_H
 
+#include <gbm.h>
 #include <pipewire/pipewire.h>
 #include <spa/param/video/format-utils.h>
 #include <wayland-client-protocol.h>
@@ -103,6 +104,9 @@ struct xdpw_screencast_context {
 	struct zxdg_output_manager_v1 *xdg_output_manager;
 	struct wl_shm *shm;
 
+	// gbm
+	struct gbm_device *gbm;
+
 	// sessions
 	struct wl_list screencast_instances;
 };
@@ -158,6 +162,7 @@ struct xdpw_wlr_output {
 };
 
 void randname(char *buf);
+struct gbm_device *xdpw_gbm_device_create(void);
 struct xdpw_buffer *xdpw_buffer_create(struct xdpw_screencast_instance *cast,
 	enum buffer_type buffer_type, struct xdpw_screencopy_frame_info *frame_info);
 void xdpw_buffer_destroy(struct xdpw_buffer *buffer);

meson.build

@@ -27,6 +27,8 @@ pipewire = dependency('libpipewire-0.3', version: '>= 0.3.41')
 wayland_client = dependency('wayland-client')
 wayland_protos = dependency('wayland-protocols', version: '>=1.14')
 iniparser = dependency('inih')
+gbm = dependency('gbm')
+drm = dependency('libdrm')
 
 epoll = dependency('', required: false)
 if (not cc.has_function('timerfd_create', prefix: '#include <sys/timerfd.h>') or
@@ -92,6 +94,8 @@ executable(
 		pipewire,
 		rt,
 		iniparser,
+		gbm,
+		drm,
 		epoll,
 	],
 	include_directories: [inc],

src/screencast/screencast_common.c

@@ -6,6 +6,7 @@
 #include <sys/stat.h>
 #include <unistd.h>
 #include <libdrm/drm_fourcc.h>
+#include <xf86drm.h>
 
 #include "logger.h"
 
@@ -20,6 +21,47 @@ void randname(char *buf) {
 	}
 }
 
+static char *gbm_find_render_node() {
+	drmDevice *devices[64];
+	char *render_node = NULL;
+
+	int n = drmGetDevices2(0, devices, sizeof(devices) / sizeof(devices[0]));
+	for (int i = 0; i < n; ++i) {
+		drmDevice *dev = devices[i];
+		if (!(dev->available_nodes & (1 << DRM_NODE_RENDER)))
+			continue;
+
+		render_node = strdup(dev->nodes[DRM_NODE_RENDER]);
+		break;
+	}
+
+	drmFreeDevices(devices, n);
+	return render_node;
+}
+
+struct gbm_device *xdpw_gbm_device_create(void) {
+	struct gbm_device *gbm;
+	char *render_node = NULL;
+
+	render_node = gbm_find_render_node();
+	if (render_node == NULL) {
+		logprint(ERROR, "xdpw: Could not find render node");
+		return NULL;
+	}
+	logprint(INFO, "xdpw: Using render node %s", render_node);
+
+	int fd = open(render_node, O_RDWR | O_CLOEXEC);
+	if (fd < 0) {
+		logprint(ERROR, "xdpw: Could not open render node %s", render_node);
+		free(render_node);
+		return NULL;
+	}
+
+	free(render_node);
+	gbm = gbm_create_device(fd);
+	return gbm;
+}
+
 static int anonymous_shm_open(void) {
 	char name[] = "/xdpw-shm-XXXXXX";
 	int retries = 100;

src/screencast/wlr_screencast.c

@@ -641,6 +641,12 @@ int xdpw_wlr_screencopy_init(struct xdpw_state *state) {
 		return -1;
 	}
 
+	// make sure we have a gbm device
+	ctx->gbm = xdpw_gbm_device_create();
+	if (!ctx->gbm) {
+		logprint(ERROR, "System doesn't support gbm!");
+	}
+
 	return 0;
 }
 
@@ -666,6 +672,11 @@ void xdpw_wlr_screencopy_finish(struct xdpw_screencast_context *ctx) {
 	if (ctx->xdg_output_manager) {
 		zxdg_output_manager_v1_destroy(ctx->xdg_output_manager);
 	}
+	if (ctx->gbm) {
+		int fd = gbm_device_get_fd(ctx->gbm);
+		gbm_device_destroy(ctx->gbm);
+		close(fd);
+	}
 	if (ctx->registry) {
 		wl_registry_destroy(ctx->registry);
 	}