screencast: get supported format modifier pairs from wlroots

Registering a zwp_linux_dmabuf_v1_listener gives access to the supported
format modifier pairs of the compositor.

This handler emits events for each format modifier pair. Those are stored
and will later be used to announce capabilities via PipeWire.

include/screencast_common.h

@@ -91,6 +91,12 @@ struct xdpw_buffer {
 	struct wl_buffer *buffer;
 };
 
+struct xdpw_format_modifier_pair {
+	struct wl_list link;
+	uint32_t fourcc;
+	uint64_t modifier;
+};
+
 struct xdpw_screencast_context {
 
 	// xdpw
@@ -107,6 +113,7 @@ struct xdpw_screencast_context {
 	struct zxdg_output_manager_v1 *xdg_output_manager;
 	struct wl_shm *shm;
 	struct zwp_linux_dmabuf_v1 *linux_dmabuf;
+	struct wl_list format_modifier_pairs;
 
 	// gbm
 	struct gbm_device *gbm;

src/screencast/wlr_screencast.c

@@ -545,6 +545,28 @@ static void wlr_remove_output(struct xdpw_wlr_output *out) {
 	free(out);
 }
 
+static void linux_dmabuf_handle_modifier(void *data,
+		struct zwp_linux_dmabuf_v1 *zwp_linux_dmabuf_v1,
+		uint32_t format, uint32_t modifier_hi, uint32_t modifier_lo) {
+	struct xdpw_screencast_context *ctx = data;
+
+	logprint(TRACE, "wlroots: linux_dmabuf_handle_modifier called");
+
+	struct xdpw_format_modifier_pair *fm_pair = calloc(1, sizeof(struct xdpw_format_modifier_pair));
+
+	fm_pair->fourcc = format;
+	fm_pair->modifier = ((((uint64_t)modifier_hi) << 32) | modifier_lo);
+
+	logprint(TRACE, "wlroots: format %u (%u)", fm_pair->fourcc, fm_pair->modifier);
+
+	wl_list_insert(&ctx->format_modifier_pairs, &fm_pair->link);
+}
+
+static const struct zwp_linux_dmabuf_v1_listener linux_dmabuf_listener = {
+	.format = noop,
+	.modifier = linux_dmabuf_handle_modifier,
+};
+
 static void wlr_registry_handle_add(void *data, struct wl_registry *reg,
 		uint32_t id, const char *interface, uint32_t ver) {
 	struct xdpw_screencast_context *ctx = data;
@@ -589,6 +611,8 @@ static void wlr_registry_handle_add(void *data, struct wl_registry *reg,
 	if (strcmp(interface, zwp_linux_dmabuf_v1_interface.name) == 0) {
 		logprint(DEBUG, "wlroots: |-- registered to interface %s (Version %u)", interface, LINUX_DMABUF_VERSION);
 		ctx->linux_dmabuf = wl_registry_bind(reg, id, &zwp_linux_dmabuf_v1_interface, LINUX_DMABUF_VERSION);
+
+		zwp_linux_dmabuf_v1_add_listener(ctx->linux_dmabuf, &linux_dmabuf_listener, ctx);
 	}
 }
 
@@ -615,6 +639,9 @@ int xdpw_wlr_screencopy_init(struct xdpw_state *state) {
 	// initialize a list of active screencast instances
 	wl_list_init(&ctx->screencast_instances);
 
+	// initialize a list of format modifier pairs
+	wl_list_init(&ctx->format_modifier_pairs);
+
 	// retrieve registry
 	ctx->registry = wl_display_get_registry(state->wl_display);
 	wl_registry_add_listener(ctx->registry, &wlr_registry_listener, ctx);
@@ -659,6 +686,12 @@ int xdpw_wlr_screencopy_init(struct xdpw_state *state) {
 }
 
 void xdpw_wlr_screencopy_finish(struct xdpw_screencast_context *ctx) {
+	struct xdpw_format_modifier_pair *fm_pair, *tmp_fmp;
+	wl_list_for_each_safe(fm_pair, tmp_fmp, &ctx->format_modifier_pairs, link) {
+		wl_list_remove(&fm_pair->link);
+		free(fm_pair);
+	}
+
 	struct xdpw_wlr_output *output, *tmp_o;
 	wl_list_for_each_safe(output, tmp_o, &ctx->output_list, link) {
 		wl_list_remove(&output->link);