backend/drm: improve CRTC reallocation pretty printing

Only print the list of connectors once, with both the old and new
status. Use CRTC object IDs instead of CRTC indices. Make it obvious
when a connector keeps the same CRTC.

backend/drm/drm.c

@@ -1216,6 +1216,14 @@ static void dealloc_crtc(struct wlr_drm_connector *conn) {
 	wlr_output_state_finish(&state);
 }
 
+static void format_nullable_crtc(char *str, size_t size, struct wlr_drm_crtc *crtc) {
+	if (crtc != NULL) {
+		snprintf(str, size, "CRTC %"PRIu32, crtc->id);
+	} else {
+		snprintf(str, size, "no CRTC");
+	}
+}
+
 static void realloc_crtcs(struct wlr_drm_backend *drm,
 		struct wlr_drm_connector *want_conn) {
 	assert(drm->num_crtcs > 0);
@@ -1236,7 +1244,6 @@ static void realloc_crtcs(struct wlr_drm_backend *drm,
 		previous_match[i] = UNMATCHED;
 	}
 
-	wlr_log(WLR_DEBUG, "State before reallocation:");
 	size_t i = 0;
 	struct wlr_drm_connector *conn;
 	wl_list_for_each(conn, &drm->connectors, link) {
@@ -1250,10 +1257,6 @@ static void realloc_crtcs(struct wlr_drm_backend *drm,
 		// connector the user wants to enable
 		bool want_crtc = conn == want_conn || conn->output.enabled;
 
-		wlr_log(WLR_DEBUG, "  '%s': crtc=%d status=%s want_crtc=%d",
-			conn->name, conn->crtc ? (int)(conn->crtc - drm->crtcs) : -1,
-			drm_connector_status_str(conn->status), want_crtc);
-
 		if (conn->status == DRM_MODE_CONNECTED && want_crtc) {
 			connector_constraints[i] = conn->possible_crtcs;
 		} else {
@@ -1278,6 +1281,31 @@ static void realloc_crtcs(struct wlr_drm_backend *drm,
 		}
 	}
 
+	for (size_t i = 0; i < num_connectors; ++i) {
+		struct wlr_drm_connector *conn = connectors[i];
+
+		struct wlr_drm_crtc *new_crtc = NULL;
+		if (connector_match[i] >= 0) {
+			new_crtc = &drm->crtcs[connector_match[i]];
+		}
+
+		char old_crtc_str[16], new_crtc_str[16];
+		format_nullable_crtc(old_crtc_str, sizeof(old_crtc_str), conn->crtc);
+		format_nullable_crtc(new_crtc_str, sizeof(new_crtc_str), new_crtc);
+
+		char crtc_str[64];
+		if (conn->crtc != new_crtc) {
+			snprintf(crtc_str, sizeof(crtc_str), "%s → %s", old_crtc_str, new_crtc_str);
+		} else {
+			snprintf(crtc_str, sizeof(crtc_str), "%s (no change)", new_crtc_str);
+		}
+
+		wlr_log(WLR_DEBUG, "  Connector %s (%s%s): %s",
+			conn->name, drm_connector_status_str(conn->status),
+			connector_constraints[i] != 0 ? ", needs CRTC" : "",
+			crtc_str);
+	}
+
 	// Refuse to remove a CRTC from an enabled connector, and refuse to
 	// change the CRTC of an enabled connector.
 	for (size_t i = 0; i < num_connectors; ++i) {
@@ -1299,13 +1327,9 @@ static void realloc_crtcs(struct wlr_drm_backend *drm,
 	}
 
 	// Apply new configuration
-	wlr_log(WLR_DEBUG, "State after reallocation:");
 	for (size_t i = 0; i < num_connectors; ++i) {
 		struct wlr_drm_connector *conn = connectors[i];
 
-		wlr_log(WLR_DEBUG, "  '%s': crtc=%zd",
-			conn->name, connector_match[i]);
-
 		if (conn->crtc != NULL && connector_match[i] == conn->crtc - drm->crtcs) {
 			// We don't need to change anything
 			continue;