Allow a fallback color to be specified for swaybg

This allows for a color to be set when the wallpaper does not fill the
entire output. If specified, the fallback color is also used when the
image path is inaccessible.

include/sway/config.h

@@ -151,6 +151,7 @@ struct output_config {
 
 	char *background;
 	char *background_option;
+	char *background_fallback;
 	enum config_dpms dpms_state;
 };
 

sway/commands/output/background.c

@@ -6,6 +6,7 @@
 #include <errno.h>
 #include "sway/commands.h"
 #include "sway/config.h"
+#include "sway/swaynag.h"
 #include "log.h"
 #include "stringop.h"
 
@@ -36,6 +37,7 @@ struct cmd_results *output_cmd_background(int argc, char **argv) {
 		output->background = calloc(1, strlen(argv[0]) + 3);
 		snprintf(output->background, strlen(argv[0]) + 3, "\"%s\"", argv[0]);
 		output->background_option = strdup("solid_color");
+		output->background_fallback = NULL;
 		argc -= 2; argv += 2;
 	} else {
 		bool valid = false;
@@ -104,16 +106,35 @@ struct cmd_results *output_cmd_background(int argc, char **argv) {
 			free(conf);
 		}
 
-		if (access(src, F_OK) == -1) {
-			struct cmd_results *cmd_res = cmd_results_new(CMD_FAILURE, "output",
-				"Unable to access background file '%s': %s", src, strerror(errno));
-			free(src);
-			return cmd_res;
+		bool can_access = access(src, F_OK) != -1;
+		if (!can_access) {
+			wlr_log(WLR_ERROR, "Unable to access background file '%s': %s",
+					src, strerror(errno));
+			if (!config->validating) {
+				swaynag_log(config->swaynag_command,
+						&config->swaynag_config_errors,
+						"Unable to access background file '%s'", src);
 			}
-
+			free(src);
+		} else {
 			output->background = src;
 			output->background_option = strdup(mode);
+		}
 		argc -= j + 1; argv += j + 1;
+
+		output->background_fallback = NULL;
+		if (argc && *argv[0] == '#') {
+			output->background_fallback = calloc(1, strlen(argv[0]) + 3);
+			snprintf(output->background_fallback, strlen(argv[0]) + 3,
+					"\"%s\"", argv[0]);
+			argc--; argv++;
+
+			if (!can_access) {
+				output->background = output->background_fallback;
+				output->background_option = strdup("solid_color");
+				output->background_fallback = NULL;
+			}
+		}
 	}
 
 	config->handler_context.leftovers.argc = argc;

sway/config/output.c

@@ -77,6 +77,10 @@ void merge_output_config(struct output_config *dst, struct output_config *src) {
 		free(dst->background_option);
 		dst->background_option = strdup(src->background_option);
 	}
+	if (src->background_fallback) {
+		free(dst->background_fallback);
+		dst->background_fallback = strdup(src->background_fallback);
+	}
 	if (src->dpms_state != 0) {
 		dst->dpms_state = src->dpms_state;
 	}
@@ -226,17 +230,19 @@ void apply_output_config(struct output_config *oc, struct sway_container *output
 		wlr_log(WLR_DEBUG, "Setting background for output %d to %s",
 				output_i, oc->background);
 
-		size_t len = snprintf(NULL, 0, "%s %d %s %s",
+		size_t len = snprintf(NULL, 0, "%s %d %s %s %s",
 				config->swaybg_command ? config->swaybg_command : "swaybg",
-				output_i, oc->background, oc->background_option);
+				output_i, oc->background, oc->background_option,
+				oc->background_fallback ? oc->background_fallback : "");
 		char *command = malloc(len + 1);
 		if (!command) {
 			wlr_log(WLR_DEBUG, "Unable to allocate swaybg command");
 			return;
 		}
-		snprintf(command, len + 1, "%s %d %s %s",
+		snprintf(command, len + 1, "%s %d %s %s %s",
 				config->swaybg_command ? config->swaybg_command : "swaybg",
-				output_i, oc->background, oc->background_option);
+				output_i, oc->background, oc->background_option,
+				oc->background_fallback ? oc->background_fallback : "");
 		wlr_log(WLR_DEBUG, "-> %s", command);
 
 		char *const cmd[] = { "sh", "-c", command, NULL };

sway/sway.5.scd

@@ -489,9 +489,13 @@ The default colors are:
 	setting an integral scale factor and adjusting the font size of your
 	applications to taste.
 
-*output* <name> background|bg <file> <mode>
+*output* <name> background|bg <file> <mode> [<fallback\_color>]
 	Sets the wallpaper for the given output to the specified file, using the
-	given scaling mode (one of "stretch", "fill", "fit", "center", "tile").
+	given scaling mode (one of "stretch", "fill", "fit", "center", "tile"). If
+	the specified file cannot be accessed or if the image does fill the entire
+	output, a fallback color may be provided to cover the rest of the output.
+	__fallback\_color__ should be specified as _#RRGGBB_. Alpha is not
+	supported.
 
 **output** <name> background|bg <color> solid\_color
 	Sets the background of the given output to the specified color. _color_

swaybg/main.c

@@ -17,6 +17,7 @@ struct swaybg_args {
 	int output_idx;
 	const char *path;
 	enum background_mode mode;
+	const char *fallback;
 };
 
 struct swaybg_context {
@@ -76,6 +77,10 @@ static void render_frame(struct swaybg_state *state) {
 		cairo_set_source_u32(cairo, state->context.color);
 		cairo_paint(cairo);
 	} else {
+		if (state->args->fallback && state->context.color) {
+			cairo_set_source_u32(cairo, state->context.color);
+			cairo_paint(cairo);
+		}
 		render_background_image(cairo, state->context.image,
 				state->args->mode, buffer_width, buffer_height);
 	}
@@ -91,6 +96,9 @@ static bool prepare_context(struct swaybg_state *state) {
 		state->context.color = parse_color(state->args->path);
 		return is_valid_color(state->args->path);
 	}
+	if (state->args->fallback && is_valid_color(state->args->fallback)) {
+		state->context.color = parse_color(state->args->fallback);
+	}
 	if (!(state->context.image = load_background_image(state->args->path))) {
 		return false;
 	}
@@ -190,7 +198,7 @@ int main(int argc, const char **argv) {
 	state.args = &args;
 	wlr_log_init(WLR_DEBUG, NULL);
 
-	if (argc != 4) {
+	if (argc < 4 || argc > 5) {
 		wlr_log(WLR_ERROR, "Do not run this program manually. "
 				"See man 5 sway and look for output options.");
 		return 1;
@@ -202,6 +210,9 @@ int main(int argc, const char **argv) {
 	if (args.mode == BACKGROUND_MODE_INVALID) {
 		return 1;
 	}
+
+	args.fallback = argc == 5 ? argv[4] : NULL;
+
 	if (!prepare_context(&state)) {
 		return 1;
 	}