Implement opacity command

sway/commands/opacity.c

@@ -0,0 +1,39 @@
+#include <assert.h>
+#include <stdlib.h>
+#include "sway/commands.h"
+#include "sway/tree/view.h"
+#include "log.h"
+
+static bool parse_opacity(const char *opacity, float *val) {
+	char *err;
+	*val = strtof(opacity, &err);
+	if (*val < 0 || *val > 1 || *err) {
+		return false;
+	}
+	return true;
+}
+
+struct cmd_results *cmd_opacity(int argc, char **argv) {
+	struct cmd_results *error = NULL;
+	if ((error = checkarg(argc, "layout", EXPECTED_EQUAL_TO, 1))) {
+		return error;
+	}
+
+	struct sway_container *con =
+		config->handler_context.current_container;
+
+	float opacity = 0.0f;
+
+	if (!parse_opacity(argv[0], &opacity)) {
+		return cmd_results_new(CMD_INVALID, "opacity <value>",
+				"Invalid value (expected 0..1): %s", argv[0]);
+	}
+
+	con->alpha = opacity;
+
+	if (con->type == C_VIEW) {
+		view_damage_whole(con->sway_view);
+	}
+
+	return cmd_results_new(CMD_SUCCESS, NULL, NULL);
+}