From 6e773592f647fdc0f937e10da73ba9067097806d Mon Sep 17 00:00:00 2001
From: Consolatis <35009135+Consolatis@users.noreply.github.com>
Date: Mon, 22 Jan 2024 15:21:18 +0100
Subject: [PATCH] src/output.c: properly test new output configurations

Fixes #1458
---
 src/output.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 63 insertions(+), 1 deletion(-)

diff --git a/src/output.c b/src/output.c
index ed039545..650a338e 100644
--- a/src/output.c
+++ b/src/output.c
@@ -7,9 +7,11 @@
  */
 
 #define _POSIX_C_SOURCE 200809L
+#include <assert.h>
 #include <strings.h>
 #include <wlr/backend/drm.h>
 #include <wlr/backend/headless.h>
+#include <wlr/backend/wayland.h>
 #include <wlr/types/wlr_buffer.h>
 #include <wlr/types/wlr_drm_lease_v1.h>
 #include <wlr/types/wlr_output.h>
@@ -483,8 +485,68 @@ output_config_apply(struct server *server,
 static bool
 verify_output_config_v1(const struct wlr_output_configuration_v1 *config)
 {
-	/* TODO implement */
+	const char *err_msg = NULL;
+	struct wlr_output_configuration_head_v1 *head;
+	wl_list_for_each(head, &config->heads, link) {
+		if (!head->state.enabled) {
+			continue;
+		}
+
+		/* Handle custom modes */
+		if (!head->state.mode) {
+			int32_t refresh = head->state.custom_mode.refresh;
+
+			if (wlr_output_is_drm(head->state.output) && refresh == 0) {
+				/*
+				 * wlroots has a bug which causes a divide by zero
+				 * when setting the refresh rate to 0 on a DRM output.
+				 * It is already fixed but not part of an official 0.17.x
+				 * release. Even it would be we still need to carry the
+				 * fix here to prevent older 0.17.x releases from crashing.
+				 *
+				 * https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/3791
+				 */
+				err_msg = "DRM backend does not support a refresh rate of 0";
+				goto custom_mode_failed;
+			}
+
+			if (wlr_output_is_wl(head->state.output) && refresh != 0) {
+				/* Wayland backend does not support refresh rates */
+				err_msg = "Wayland backend refresh rate unsupported";
+				goto custom_mode_failed;
+			}
+		}
+
+		/*
+		 * Ensure the new output state can be applied on
+		 * its own and inform the client when it can not.
+		 *
+		 * Applying the changes may still fail later when
+		 * getting mixed with wlr_output->pending which
+		 * may contain further unrelated changes.
+		 */
+		struct wlr_output_state output_state;
+		wlr_output_state_init(&output_state);
+		wlr_output_head_v1_state_apply(&head->state, &output_state);
+
+		if (!wlr_output_test_state(head->state.output, &output_state)) {
+			wlr_output_state_finish(&output_state);
+			return false;
+		}
+		wlr_output_state_finish(&output_state);
+	}
+
 	return true;
+
+custom_mode_failed:
+	assert(err_msg);
+	wlr_log(WLR_INFO, "%s (%s: %dx%d@%d)",
+		err_msg,
+		head->state.output->name,
+		head->state.custom_mode.width,
+		head->state.custom_mode.height,
+		head->state.custom_mode.refresh);
+	return false;
 }
 
 static void