initial fade-out groundwork

include/sway/tree/container.h

@@ -122,6 +122,7 @@ struct sway_container {
 	// TODO: move alpha to state?
 	float alpha;
 	float target_alpha;
+	float max_alpha;
 
 	int corner_radius;
 

sway/commands/opacity.c

@@ -24,9 +24,9 @@ struct cmd_results *cmd_opacity(int argc, char **argv) {
 	}
 
 	if (!strcasecmp(argv[0], "plus")) {
-		val = con->target_alpha + val;
+		val = con->max_alpha + val;
 	} else if (!strcasecmp(argv[0], "minus")) {
-		val = con->target_alpha - val;
+		val = con->max_alpha - val;
 	} else if (argc > 1 && strcasecmp(argv[0], "set")) {
 		return cmd_results_new(CMD_INVALID,
 				"Expected: set|plus|minus <0..1>: %s", argv[0]);
@@ -36,6 +36,7 @@ struct cmd_results *cmd_opacity(int argc, char **argv) {
 		return cmd_results_new(CMD_FAILURE, "opacity value out of bounds");
 	}
 
+	con->max_alpha = val;
 	con->target_alpha = val;
 	container_damage_whole(con);
 	return cmd_results_new(CMD_SUCCESS, NULL);

sway/desktop/output.c

@@ -527,19 +527,17 @@ static void containers_tick_alpha(list_t *containers, struct sway_output *output
 	}
 
 	float alpha_step;
+	struct sway_container *con = NULL;
 	for (int i = 0; i < containers->length; ++i) {
-		struct sway_container *con = containers->items[i];
+		con = containers->items[i];
 		if (con->pending.children) {
 			containers_tick_alpha(con->pending.children, output);
 		} else { // should this else be removed?
 			if (con->alpha == con->target_alpha) {
 				continue;
-			} else if (con->alpha < con->target_alpha) { // fade-in animation
-				alpha_step = (con->target_alpha * output->refresh_sec) / config->animation_duration;
-				con->alpha = MIN(con->alpha + alpha_step, con->target_alpha);
-			} else if (con->alpha > con->target_alpha) { // fade-out animation
-				// TODO
 			}
+			alpha_step = (con->max_alpha * output->refresh_sec) / config->animation_duration;
+			con->alpha = con->alpha < con->target_alpha ? MIN(con->alpha + alpha_step, con->target_alpha) : MAX(con->alpha - alpha_step, con->target_alpha);
 			output_damage_whole_container(output, con);
 		}
 	}

sway/tree/container.c

@@ -41,6 +41,7 @@ struct sway_container *container_create(struct sway_view *view) {
 	c->view = view;
 	c->alpha = 0.0f;
 	c->target_alpha = 1.0f;
+	c->max_alpha = 1.0f;
 	c->saturation = 1.0f;
 	c->dim = config->default_dim_inactive;
 	c->shadow_enabled = config->shadow_enabled;