backend: add wlr_backend_{test,commit}()

backend/backend.c

@@ -15,6 +15,7 @@
 #include "backend/backend.h"
 #include "backend/multi.h"
 #include "render/allocator/allocator.h"
+#include "types/wlr_output.h"
 #include "util/env.h"
 #include "util/time.h"
 
@@ -445,3 +446,52 @@ error:
 #endif
 	return NULL;
 }
+
+bool wlr_backend_test(struct wlr_backend *backend,
+		const struct wlr_backend_output_state *states, size_t states_len) {
+	if (backend->impl->test) {
+		return backend->impl->test(backend, states, states_len);
+	}
+
+	for (size_t i = 0; i < states_len; i++) {
+		const struct wlr_backend_output_state *state = &states[i];
+		assert(state->output->backend == backend);
+		if (!wlr_output_test_state(states[i].output, &state->base)) {
+			return false;
+		}
+	}
+
+	return true;
+}
+
+bool wlr_backend_commit(struct wlr_backend *backend,
+		const struct wlr_backend_output_state *states, size_t states_len) {
+	if (!backend->impl->commit) {
+		for (size_t i = 0; i < states_len; i++) {
+			const struct wlr_backend_output_state *state = &states[i];
+			if (!wlr_output_commit_state(state->output, &state->base)) {
+				return false;
+			}
+		}
+
+		return true;
+	}
+
+	for (size_t i = 0; i < states_len; i++) {
+		const struct wlr_backend_output_state *state = &states[i];
+		if (!output_prepare_commit(state->output, &state->base)) {
+			return false;
+		}
+	}
+
+	if (!backend->impl->commit(backend, states, states_len)) {
+		return false;
+	}
+
+	for (size_t i = 0; i < states_len; i++) {
+		const struct wlr_backend_output_state *state = &states[i];
+		output_apply_commit(state->output, &state->base);
+	}
+
+	return true;
+}

include/types/wlr_output.h

@@ -22,4 +22,7 @@ bool output_cursor_set_texture(struct wlr_output_cursor *cursor,
 
 void output_defer_present(struct wlr_output *output, struct wlr_output_event_present event);
 
+bool output_prepare_commit(struct wlr_output *output, const struct wlr_output_state *state);
+void output_apply_commit(struct wlr_output *output, const struct wlr_output_state *state);
+
 #endif

include/wlr/backend.h

@@ -10,10 +10,19 @@
 #define WLR_BACKEND_H
 
 #include <wayland-server-core.h>
+#include <wlr/types/wlr_output.h>
 
 struct wlr_session;
 struct wlr_backend_impl;
 
+/**
+ * Per-output state for wlr_backend_test() and wlr_backend_commit().
+ */
+struct wlr_backend_output_state {
+	struct wlr_output *output;
+	struct wlr_output_state base;
+};
+
 /**
  * A backend provides a set of input and output devices.
  */
@@ -62,4 +71,23 @@ void wlr_backend_destroy(struct wlr_backend *backend);
  */
 int wlr_backend_get_drm_fd(struct wlr_backend *backend);
 
+/**
+ * Atomically test a new configuration for multiple outputs.
+ *
+ * Some backends (e.g. DRM) have global backend-wide limitations. This function
+ * can be used to check whether changes across multiple outputs are supported by
+ * the backend.
+ */
+bool wlr_backend_test(struct wlr_backend *backend,
+	const struct wlr_backend_output_state *states, size_t states_len);
+/**
+ * Atomically apply a new configuration for multiple outputs.
+ *
+ * There is no guarantee that the changes will be applied atomically. Users
+ * should call wlr_backend_test() first to check that the new state is supported
+ * by the backend.
+ */
+bool wlr_backend_commit(struct wlr_backend *backend,
+	const struct wlr_backend_output_state *states, size_t states_len);
+
 #endif

include/wlr/backend/interface.h

@@ -12,11 +12,17 @@
 #include <stdbool.h>
 #include <wlr/backend.h>
 
+struct wlr_output_state;
+
 struct wlr_backend_impl {
 	bool (*start)(struct wlr_backend *backend);
 	void (*destroy)(struct wlr_backend *backend);
 	int (*get_drm_fd)(struct wlr_backend *backend);
 	uint32_t (*get_buffer_caps)(struct wlr_backend *backend);
+	bool (*test)(struct wlr_backend *backend,
+		const struct wlr_backend_output_state *states, size_t states_len);
+	bool (*commit)(struct wlr_backend *backend,
+		const struct wlr_backend_output_state *states, size_t states_len);
 };
 
 /**

types/output/output.c

@@ -663,6 +663,51 @@ bool wlr_output_test_state(struct wlr_output *output,
 	return success;
 }
 
+bool output_prepare_commit(struct wlr_output *output, const struct wlr_output_state *state) {
+	if (!output_basic_test(output, state)) {
+		wlr_log(WLR_ERROR, "Basic output test failed for %s", output->name);
+		return false;
+	}
+
+	if ((state->committed & WLR_OUTPUT_STATE_BUFFER) &&
+			output->idle_frame != NULL) {
+		wl_event_source_remove(output->idle_frame);
+		output->idle_frame = NULL;
+	}
+
+	struct timespec now;
+	clock_gettime(CLOCK_MONOTONIC, &now);
+
+	struct wlr_output_event_precommit pre_event = {
+		.output = output,
+		.when = &now,
+		.state = state,
+	};
+	wl_signal_emit_mutable(&output->events.precommit, &pre_event);
+
+	return true;
+}
+
+void output_apply_commit(struct wlr_output *output, const struct wlr_output_state *state) {
+	output->commit_seq++;
+
+	if (output_pending_enabled(output, state)) {
+		output->frame_pending = true;
+		output->needs_frame = false;
+	}
+
+	output_apply_state(output, state);
+
+	struct timespec now;
+	clock_gettime(CLOCK_MONOTONIC, &now);
+	struct wlr_output_event_commit event = {
+		.output = output,
+		.when = &now,
+		.state = state,
+	};
+	wl_signal_emit_mutable(&output->events.commit, &event);
+}
+
 bool wlr_output_commit_state(struct wlr_output *output,
 		const struct wlr_output_state *state) {
 	uint32_t unchanged = output_compare_state(output, state);
@@ -682,22 +727,10 @@ bool wlr_output_commit_state(struct wlr_output *output,
 		return false;
 	}
 
-	if ((pending.committed & WLR_OUTPUT_STATE_BUFFER) &&
+	if (!output_prepare_commit(output, &pending)) {
-			output->idle_frame != NULL) {
+		return false;
-		wl_event_source_remove(output->idle_frame);
-		output->idle_frame = NULL;
 	}
 
-	struct timespec now;
-	clock_gettime(CLOCK_MONOTONIC, &now);
-
-	struct wlr_output_event_precommit pre_event = {
-		.output = output,
-		.when = &now,
-		.state = &pending,
-	};
-	wl_signal_emit_mutable(&output->events.precommit, &pre_event);
-
 	if (!output->impl->commit(output, &pending)) {
 		if (new_back_buffer) {
 			wlr_buffer_unlock(pending.buffer);
@@ -705,21 +738,7 @@ bool wlr_output_commit_state(struct wlr_output *output,
 		return false;
 	}
 
-	output->commit_seq++;
+	output_apply_commit(output, &pending);
-
-	if (output_pending_enabled(output, state)) {
-		output->frame_pending = true;
-		output->needs_frame = false;
-	}
-
-	output_apply_state(output, &pending);
-
-	struct wlr_output_event_commit event = {
-		.output = output,
-		.when = &now,
-		.state = &pending,
-	};
-	wl_signal_emit_mutable(&output->events.commit, &event);
 
 	if (new_back_buffer) {
 		wlr_buffer_unlock(pending.buffer);