backend: introduce backend_get_buffer_caps

backend/backend.c

@@ -16,6 +16,7 @@
 #include <wlr/backend/wayland.h>
 #include <wlr/config.h>
 #include <wlr/util/log.h>
+#include "backend/backend.h"
 #include "backend/multi.h"
 
 #if WLR_HAS_X11_BACKEND
@@ -78,6 +79,14 @@ int wlr_backend_get_drm_fd(struct wlr_backend *backend) {
 	return backend->impl->get_drm_fd(backend);
 }
 
+uint32_t backend_get_buffer_caps(struct wlr_backend *backend) {
+	if (!backend->impl->get_buffer_caps) {
+		return 0;
+	}
+
+	return backend->impl->get_buffer_caps(backend);
+}
+
 static size_t parse_outputs_env(const char *name) {
 	const char *outputs_str = getenv(name);
 	if (outputs_str == NULL) {

backend/drm/backend.c

@@ -12,6 +12,7 @@
 #include <wlr/util/log.h>
 #include <xf86drm.h>
 #include "backend/drm/drm.h"
+#include "types/wlr_buffer.h"
 #include "util/signal.h"
 
 struct wlr_drm_backend *get_drm_backend_from_backend(
@@ -89,12 +90,17 @@ static int backend_get_drm_fd(struct wlr_backend *backend) {
 	}
 }
 
+static uint32_t backend_get_buffer_caps(struct wlr_backend *backend) {
+	return WLR_BUFFER_CAP_DMABUF;
+}
+
 static const struct wlr_backend_impl backend_impl = {
 	.start = backend_start,
 	.destroy = backend_destroy,
 	.get_renderer = backend_get_renderer,
 	.get_presentation_clock = backend_get_presentation_clock,
 	.get_drm_fd = backend_get_drm_fd,
+	.get_buffer_caps = backend_get_buffer_caps,
 };
 
 bool wlr_backend_is_drm(struct wlr_backend *b) {

backend/headless/backend.c

@@ -13,6 +13,7 @@
 #include "render/drm_format_set.h"
 #include "render/gbm_allocator.h"
 #include "render/wlr_renderer.h"
+#include "types/wlr_buffer.h"
 #include "util/signal.h"
 
 struct wlr_headless_backend *headless_backend_from_backend(
@@ -92,11 +93,18 @@ static int backend_get_drm_fd(struct wlr_backend *wlr_backend) {
 	return backend->drm_fd;
 }
 
+static uint32_t backend_get_buffer_caps(struct wlr_backend *wlr_backend) {
+	return WLR_BUFFER_CAP_DATA_PTR
+		| WLR_BUFFER_CAP_DMABUF
+		| WLR_BUFFER_CAP_SHM;
+}
+
 static const struct wlr_backend_impl backend_impl = {
 	.start = backend_start,
 	.destroy = backend_destroy,
 	.get_renderer = backend_get_renderer,
 	.get_drm_fd = backend_get_drm_fd,
+	.get_buffer_caps = backend_get_buffer_caps,
 };
 
 static void handle_display_destroy(struct wl_listener *listener, void *data) {

backend/wayland/backend.c

@@ -23,6 +23,7 @@
 #include "render/pixel_format.h"
 #include "render/shm_allocator.h"
 #include "render/wlr_renderer.h"
+#include "types/wlr_buffer.h"
 #include "util/signal.h"
 
 #include "drm-client-protocol.h"
@@ -364,11 +365,18 @@ static int backend_get_drm_fd(struct wlr_backend *backend) {
 	return wl->drm_fd;
 }
 
+static uint32_t backend_get_buffer_caps(struct wlr_backend *backend) {
+	struct wlr_wl_backend *wl = get_wl_backend_from_backend(backend);
+	return (wl->zwp_linux_dmabuf_v1 ? WLR_BUFFER_CAP_DMABUF : 0)
+		| (wl->shm ? WLR_BUFFER_CAP_SHM : 0);
+}
+
 static const struct wlr_backend_impl backend_impl = {
 	.start = backend_start,
 	.destroy = backend_destroy,
 	.get_renderer = backend_get_renderer,
 	.get_drm_fd = backend_get_drm_fd,
+	.get_buffer_caps = backend_get_buffer_caps,
 };
 
 bool wlr_backend_is_wl(struct wlr_backend *b) {

backend/x11/backend.c

@@ -35,6 +35,7 @@
 #include "render/gbm_allocator.h"
 #include "render/shm_allocator.h"
 #include "render/wlr_renderer.h"
+#include "types/wlr_buffer.h"
 #include "util/signal.h"
 
 // See dri2_format_for_depth in mesa
@@ -223,11 +224,18 @@ static int backend_get_drm_fd(struct wlr_backend *backend) {
 	return x11->drm_fd;
 }
 
+static uint32_t backend_get_buffer_caps(struct wlr_backend *backend) {
+	struct wlr_x11_backend *x11 = get_x11_backend_from_backend(backend);
+	return (x11->have_dri3 ? WLR_BUFFER_CAP_DMABUF : 0)
+		| (x11->have_shm ? WLR_BUFFER_CAP_SHM : 0);
+}
+
 static const struct wlr_backend_impl backend_impl = {
 	.start = backend_start,
 	.destroy = backend_destroy,
 	.get_renderer = backend_get_renderer,
 	.get_drm_fd = backend_get_drm_fd,
+	.get_buffer_caps = backend_get_buffer_caps,
 };
 
 bool wlr_backend_is_x11(struct wlr_backend *backend) {

include/backend/backend.h

@@ -0,0 +1,13 @@
+#ifndef BACKEND_WLR_BACKEND_H
+#define BACKEND_WLR_BACKEND_H
+
+#include <wlr/backend.h>
+
+/**
+ * Get the supported buffer capabilities.
+ *
+ * This functions returns a bitfield of supported wlr_buffer_cap.
+ */
+uint32_t backend_get_buffer_caps(struct wlr_backend *backend);
+
+#endif

include/wlr/backend/interface.h

@@ -20,6 +20,7 @@ struct wlr_backend_impl {
 	struct wlr_session *(*get_session)(struct wlr_backend *backend);
 	clockid_t (*get_presentation_clock)(struct wlr_backend *backend);
 	int (*get_drm_fd)(struct wlr_backend *backend);
+	uint32_t (*get_buffer_caps)(struct wlr_backend *backend);
 };
 
 /**