Wireframe: panic when enabling wireframes after startup

[jakobhellermann]

When the WireframeConfig::global setting is false at the beginning and is later changed to true, bevy panics with thread 'main' panicked at 'called Option::unwrap() on a None value', crates/bevy_render/src/pipeline/pipeline_compiler.rs:137:64

bevy/crates/bevy_render/src/pipeline/pipeline_compiler.rs

Line 137 in 1e42de6

let source_descriptor = pipelines.get(source_pipeline).unwrap();

The same happens if a Wireframe component is added to an entity later on.

To reproduce it you can take the wireframe example and add a system which enables global wireframes after startup

app.add_system(delayed_wireframe.system()

fn delayed_wireframe(
    mut wireframe_config: ResMut<WireframeConfig>,
    time: Res<Time>,
    mut query: Query<&mut Timer>,
) {
    let mut timer = query.single_mut().unwrap();
    if timer.tick(time.delta()).just_finished() {
        commands.insert(cube, Wireframe);
    }
}

 fn setup(
    mut commands: Commands,
    mut wireframe_config: ResMut<WireframeConfig>,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
+    commands.spawn((Timer::from_seconds(1.0, false),));
     // ...

[jakobhellermann]

Relevant code:

bevy/crates/bevy_render/src/wireframe/mod.rs

Lines 103 to 109 in 3a2a688

	draw_context
	.set_pipeline(
	&mut draw,
	&render_pipeline.pipeline,
	&render_pipeline.specialization,
	)
	.unwrap();

[simgt]

It seems to be due to the initialisation of the pipeline in the Plugin::build method:

bevy/crates/bevy_render/src/wireframe/mod.rs

Lines 31 to 39 in 3a2a688

	let world = app.world_mut().cell();
	let mut shaders = world.get_resource_mut::<Assets<Shader>>().unwrap();
	let mut pipelines = world
	.get_resource_mut::<Assets<PipelineDescriptor>>()
	.unwrap();
	pipelines.set(
	WIREFRAME_PIPELINE_HANDLE,
	pipeline::build_wireframe_pipeline(&mut shaders),
	);

The code bellow solves the issue for me:

diff --git a/crates/bevy_render/src/wireframe/mod.rs b/crates/bevy_render/src/wireframe/mod.rs
index 4251fb44..4ff46866 100644
--- a/crates/bevy_render/src/wireframe/mod.rs
+++ b/crates/bevy_render/src/wireframe/mod.rs
@@ -10,7 +10,7 @@ use bevy_asset::{Assets, Handle, HandleUntyped};
 use bevy_ecs::{
     query::With,
     reflect::ReflectComponent,
-    system::{IntoSystem, Query, QuerySet, Res},
+    system::{IntoSystem, Query, QuerySet, Res, ResMut},
     world::Mut,
 };
 use bevy_reflect::{Reflect, TypeUuid};
@@ -27,19 +27,21 @@ pub struct WireframePlugin;
 impl Plugin for WireframePlugin {
     fn build(&self, app: &mut AppBuilder) {
         app.init_resource::<WireframeConfig>()
+            .add_system_to_stage(crate::CoreStage::PreUpdate, setup_pipeline_system.system())
             .add_system_to_stage(crate::RenderStage::Draw, draw_wireframes_system.system());
-        let world = app.world_mut().cell();
-        let mut shaders = world.get_resource_mut::<Assets<Shader>>().unwrap();
-        let mut pipelines = world
-            .get_resource_mut::<Assets<PipelineDescriptor>>()
-            .unwrap();
-        pipelines.set(
-            WIREFRAME_PIPELINE_HANDLE,
-            pipeline::build_wireframe_pipeline(&mut shaders),
-        );
     }
 }
 
+pub fn setup_pipeline_system(
+    mut shaders: ResMut<Assets<Shader>>,
+    mut pipelines: ResMut<Assets<PipelineDescriptor>>
+) {
+    pipelines.set(
+        WIREFRAME_PIPELINE_HANDLE,
+        pipeline::build_wireframe_pipeline(&mut shaders),
+    );
+}
+

...but rebuilding/resetting the pipeline before each update is likely not what we want. So fixing it will likely require a different path, which I won't take since I have absolutely no idea what I'm doing. 🙄

Maybe @Neo-Zhixing has some idea?

[simgt]

Still messing with things I don't understand, that solves the issue:

diff --git a/crates/bevy_render/src/wireframe/mod.rs b/crates/bevy_render/src/wireframe/mod.rs
index 4251fb44..b2ad852a 100644
--- a/crates/bevy_render/src/wireframe/mod.rs
+++ b/crates/bevy_render/src/wireframe/mod.rs
@@ -33,7 +33,7 @@ impl Plugin for WireframePlugin {
         let mut pipelines = world
             .get_resource_mut::<Assets<PipelineDescriptor>>()
             .unwrap();
-        pipelines.set(
+        pipelines.set_untracked(
             WIREFRAME_PIPELINE_HANDLE,
             pipeline::build_wireframe_pipeline(&mut shaders),
         );

I guess the problem is that because the Handle returned by Assets<PipelineDescriptor>::set() is "Strong", the asset gets freed, somehow? Or something.