Draft: ext-screencopy-v1

This is the second draft of the ext-screencopy-v1 protocol implementation.

Some things are not yet implemented, most notable of which is any sort of output transform handling with regard to cursor rendering.

Sway requires the following change for enabling the protocol:

diff --git a/sway/server.c b/sway/server.c
index 8de9f629..82a80de5 100644
--- a/sway/server.c
+++ b/sway/server.c
@@ -23,6 +23,7 @@
 #include <wlr/types/wlr_primary_selection_v1.h>
 #include <wlr/types/wlr_relative_pointer_v1.h>
 #include <wlr/types/wlr_screencopy_v1.h>
+#include <wlr/types/wlr_zext_screencopy_v1.h>
 #include <wlr/types/wlr_server_decoration.h>
 #include <wlr/types/wlr_subcompositor.h>
 #include <wlr/types/wlr_tablet_v2.h>
@@ -196,6 +197,7 @@ bool server_init(struct sway_server *server) {
 
 	wlr_export_dmabuf_manager_v1_create(server->wl_display);
 	wlr_screencopy_manager_v1_create(server->wl_display);
+	wlr_zext_screencopy_manager_v1_create(server->wl_display);
 	wlr_data_control_manager_v1_create(server->wl_display);
 	wlr_primary_selection_v1_device_manager_create(server->wl_display);
 	wlr_viewporter_create(server->wl_display);

For testing, it's useful to enable hardware cursors in the headless backend:

diff --git a/backend/headless/output.c b/backend/headless/output.c
index f03d6ee0..ef2362d7 100644
--- a/backend/headless/output.c
+++ b/backend/headless/output.c
@@ -73,6 +73,16 @@ static bool output_commit(struct wlr_output *wlr_output) {
 	return true;
 }
 
+static bool output_set_cursor(struct wlr_output *wlr_output,
+		struct wlr_buffer *wlr_buffer, int hotspot_x, int hotspot_y) {
+	return true;
+}
+
+static bool output_move_cursor(struct wlr_output *_output, int x, int y) {
+	// TODO: only return true if x == current x and y == current y
+	return true;
+}
+
 static void output_destroy(struct wlr_output *wlr_output) {
 	struct wlr_headless_output *output =
 		headless_output_from_output(wlr_output);
@@ -84,6 +94,8 @@ static void output_destroy(struct wlr_output *wlr_output) {
 static const struct wlr_output_impl output_impl = {
 	.destroy = output_destroy,
 	.commit = output_commit,
+	.set_cursor = output_set_cursor,
+	.move_cursor = output_move_cursor,
 };
 
 bool wlr_output_is_headless(struct wlr_output *wlr_output) {