fullscreen (#360)

* fullscreen

* improvements, and error catching

* yarn prettier

* discord rpc

* fixed uninitialized options.txt

* working discord version

* incorrect boolean

* change

* merge issue; regex solution

* fixed error

* multi line mode

* moved \n to start

theseus/src/api/profile/mod.rs

@@ -7,7 +7,9 @@ use crate::event::LoadingBarType;
 use crate::pack::install_from::{
     EnvType, PackDependency, PackFile, PackFileHash, PackFormat,
 };
-use crate::prelude::{JavaVersion, ProfilePathId, ProjectPathId};
+use crate::prelude::{
+    JavaVersion, ProfilePathId, ProjectPathId, SetFullscreen,
+};
 use crate::state::ProjectMetadata;
 
 use crate::util::io::{self, IOError};
@@ -838,9 +840,23 @@ pub async fn run_credentials(
         None
     };
 
+    // Any options.txt settings that we want set, add here
+    let mut mc_set_options: Vec<(String, String)> = Vec::new();
+    match profile.force_fullscreen {
+        SetFullscreen::LeaveUnset => {}
+        SetFullscreen::SetWindowed => {
+            mc_set_options
+                .push(("fullscreen".to_string(), "false".to_string()));
+        }
+        SetFullscreen::SetFullscreen => {
+            mc_set_options.push(("fullscreen".to_string(), "true".to_string()));
+        }
+    }
+
     let mc_process = crate::launcher::launch_minecraft(
         java_args,
         env_args,
+        &mc_set_options,
         wrapper,
         &memory,
         &resolution,