Not sure if this is the new format, but quickly looking I couldn't wind a easy way to update it in the book
# Objective
* For sample project to compile after first pages of book
got:
```
= note: clang: error: invalid linker name in argument '-fuse-ld=/usr/local/bin/zld'
error: linking with `cc` failed: exit status: 1
```
## Solution
FIx to correct zld path
This makes it possible for materials to configure front or
back face culling, or disable culling.
Initially I looked at specializing the Mesh which currently
controls this state but conceptually it seems more appropriate
to control this at the material level, not the mesh level.
_Just for reference this also seems to be consistent with Unity
where materials/shaders can configure the culling mode between
front/back/off - as opposed to configuring any culling state
when importing a mesh._
After some archaeology, trying to understand how this might
relate to the existing 'double_sided' option, it was determined
that double_sided is a more high level lighting option originally
from Filament that will cause the normals for back faces to be
flipped.
For sake of avoiding complexity, but keeping control this
currently keeps the options orthogonal, and adds some clarifying
documentation for `double_sided`. This won't affect any existing
apps since there hasn't been a way to disable backface culling
up until now, so the option was essentially redundant.
double_sided support could potentially be updated to imply
disabling of backface culling.
For reference https://github.com/bevyengine/bevy/pull/3734/commits also looks at exposing cull mode control. I think the main difference here is that this patch handles RenderPipelineDescriptor specialization directly within the StandardMaterial implementation instead of communicating info back to the Mesh via the `queue_material_meshes` system.
With the way material.rs builds up the final RenderPipelineDescriptor first by calling specialize for the MeshPipeline followed by specialize for the material then it seems like we have a natural place to override anything in the descriptor that's first configured for the mesh state.
# Objective
Add Visibility for lights
## Solution
- add Visibility to PointLightBundle and DirectionLightBundle
- filter lights used by Visibility.is_visible
note: includes changes from #3916 due to overlap, will be cleaner after that is merged
# Objective
When developing plugins, I very often come up to the need to have logging information printed out. The exact syntax is a bit cryptic, and takes some time to find the documentation.
Also a minor typo fix in `It has the same syntax as` part
## Solution
Adding a direct example in the module level information for both:
1. Enabling a specific level (`trace` in the example) for a module and all its subsystems at App init
2. Doing the same from console, when launching the application
Adds a `default()` shorthand for `Default::default()` ... because life is too short to constantly type `Default::default()`.
```rust
use bevy::prelude::*;
#[derive(Default)]
struct Foo {
bar: usize,
baz: usize,
}
// Normally you would do this:
let foo = Foo {
bar: 10,
..Default::default()
};
// But now you can do this:
let foo = Foo {
bar: 10,
..default()
};
```
The examples have been adapted to use `..default()`. I've left internal crates as-is for now because they don't pull in the bevy prelude, and the ergonomics of each case should be considered individually.
# Objective
fix#3915
## Solution
the issues are caused by
- lights are assigned to clusters before being filtered down to MAX_POINT_LIGHTS, leading to cluster counts potentially being too high
- after fixing the above, packing the count into 8 bits still causes overflow with exactly 256 lights affecting a cluster
to fix:
```assign_lights_to_clusters```
- limit extracted lights to MAX_POINT_LIGHTS, selecting based on shadow-caster & intensity (if required)
- warn if MAX_POINT_LIGHT count is exceeded
```prepare_lights```
- limit the lights assigned to a cluster to CLUSTER_COUNT_MASK (which is 1 less than MAX_POINT_LIGHTS) to avoid overflowing into the offset bits
notes:
- a better solution to the overflow may be to use more than 8 bits for cluster_count (the comment states only 14 of the remaining 24 bits are used for the offset). this would touch more of the code base but i'm happy to try if it has some benefit.
- intensity is only one way to select lights. it may be worth allowing user configuration of the light filtering, but i can't see a clean way to do that
# Objective
- Add ways to control how audio is played
## Solution
- playing a sound will return a (weak) handle to an asset that can be used to control playback
- if the asset is dropped, it will detach the sink (same behaviour as now)
# Objective
- Help debug panics
## Solution
- Insert a custom panic hook when trace is enabled that will log spans
example when running a command on a despawned entity
before:
```
thread 'main' panicked at 'Could not add a component (of type `panic::Marker`) to entity 1v0 because it doesn't exist in this World.
If this command was added to a newly spawned entity, ensure that you have not despawned that entity within the same stage.
This may have occurred due to system order ambiguity, or if the spawning system has multiple command buffers', /bevy/crates/bevy_ecs/src/system/commands/mod.rs:664:13
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```
after:
```
0: bevy_ecs::schedule::stage::system_commands
with name="panic::my_bad_system"
at crates/bevy_ecs/src/schedule/stage.rs:871
1: bevy_ecs::schedule::stage
with name=Update
at crates/bevy_ecs/src/schedule/mod.rs:340
2: bevy_app::app::frame
at crates/bevy_app/src/app.rs:111
3: bevy_app::app::bevy_app
at crates/bevy_app/src/app.rs:126
thread 'main' panicked at 'Could not add a component (of type `panic::Marker`) to entity 1v0 because it doesn't exist in this World.
If this command was added to a newly spawned entity, ensure that you have not despawned that entity within the same stage.
This may have occurred due to system order ambiguity, or if the spawning system has multiple command buffers', /bevy/crates/bevy_ecs/src/system/commands/mod.rs:664:13
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```
# Objective
- Optimize assign_lights_to_clusters
## Solution
- Avoid inserting entities into hash sets in inner loops when it is known they will be inserted in at least one iteration of the loop.
- Use a Vec instead of a hash set where the set is not needed
- Avoid explicit calculation of the cluster_index from x,y,z coordinates, instead using row and column offsets and just adding z in the inner loop
- These changes cut the time spent in the system roughly in half
# Objective
- Currently there is now way of making an indirect draw call from a tracked render pass.
- This is a very useful feature for GPU based rendering.
## Solution
- Expose the `draw_indirect` and `draw_indexed_indirect` methods from the wgpu `RenderPass` in the `TrackedRenderPass`.
## Alternative
- #3595: Expose the underlying `RenderPass` directly
# Objective
- In the large majority of cases, users were calling `.unwrap()` immediately after `.get_resource`.
- Attempting to add more helpful error messages here resulted in endless manual boilerplate (see #3899 and the linked PRs).
## Solution
- Add an infallible variant named `.resource` and so on.
- Use these infallible variants over `.get_resource().unwrap()` across the code base.
## Notes
I did not provide equivalent methods on `WorldCell`, in favor of removing it entirely in #3939.
## Migration Guide
Infallible variants of `.get_resource` have been added that implicitly panic, rather than needing to be unwrapped.
Replace `world.get_resource::<Foo>().unwrap()` with `world.resource::<Foo>()`.
## Impact
- `.unwrap` search results before: 1084
- `.unwrap` search results after: 942
- internal `unwrap_or_else` calls added: 4
- trivial unwrap calls removed from tests and code: 146
- uses of the new `try_get_resource` API: 11
- percentage of the time the unwrapping API was used internally: 93%
@BlackPhlox kindly pointed out and resolved a couple of inconsistencies in the bevy logo:
* The arc of the first bird's back had three vertices right next to each other, which created a noticeable sharp edge. This replaces them with a single vertex.
* The bottom part of the tail had a sharp edge, which was inconsistent with the top part of the tail. This was rounded out to mirror the top part.
I also took the chance to clean up some of the variants and (hopefully) improve the "bevy_logo_light_dark_and_dimmed" variant to improve how it renders on dark themes.
# Objective
Continuation of #2663 due to git problems - better documentation for Query::par_for_each and par_for_each_mut
## Solution
Going into more detail about the function parameters
All other examples dont have "2d" prefix in their names (even though they are in 2d folder) and reading README makes user think that example is named "rotation" not "2d_rotation" hence rename PR
# Objective
- Remove discrepancy between example name in documentation and in cargo
## Solution
- Rename example in cargo file
# Objective
The `#[reflect_trait]` macro did not maintain the visibility of its trait. It also did not make its accessor methods public, which made them inaccessible outside the current module.
## Solution
Made the `Reflect***` struct match the visibility of its trait and made both the `get` and `get_mut` methods always public.
# Objective
- Fix the ugliness of the `config` api.
- Supercedes #2440, #2463, #2491
## Solution
- Since #2398, capturing closure systems have worked.
- Use those instead where we needed config before
- Remove the rest of the config api.
- Related: #2777
# Objective
rg3d has been renamed to Fyrox for a little while now and we should reflect that. It's not particularly urgent since the old link redirects to Fyrox.
## Solution
Rename rg3d to Fyrox in the README
# Objective
`Vec3A` is does not implement `Reflect`. This is generally useful for `Reflect` derives using `Vec3A` fields, and may speed up some animation blending use cases.
## Solution
Extend the existing macro uses to include `Vec3A`.
# Objective
- Fixes#4010, as well as any similar issues in this class.
- Winit functions used outside of the main thread can cause the application to unexpectedly hang.
## Solution
- Make the `WinitWindows` resource `!Send`.
- This ensures that any systems that use `WinitWindows` must either be exclusive (run on the main thread), or the resource is explicitly marked with the `NonSend` parameter in user systems.
# Objective
Will fix#3377 and #3254
## Solution
Use an enum to represent either a `WindowId` or `Handle<Image>` in place of `Camera::window`.
Co-authored-by: Carter Anderson <mcanders1@gmail.com>
# Objective
- Closes#786
- Closes#2252
- Closes#2588
This PR implements a derive macro that allows users to define their queries as structs with named fields.
## Example
```rust
#[derive(WorldQuery)]
#[world_query(derive(Debug))]
struct NumQuery<'w, T: Component, P: Component> {
entity: Entity,
u: UNumQuery<'w>,
generic: GenericQuery<'w, T, P>,
}
#[derive(WorldQuery)]
#[world_query(derive(Debug))]
struct UNumQuery<'w> {
u_16: &'w u16,
u_32_opt: Option<&'w u32>,
}
#[derive(WorldQuery)]
#[world_query(derive(Debug))]
struct GenericQuery<'w, T: Component, P: Component> {
generic: (&'w T, &'w P),
}
#[derive(WorldQuery)]
#[world_query(filter)]
struct NumQueryFilter<T: Component, P: Component> {
_u_16: With<u16>,
_u_32: With<u32>,
_or: Or<(With<i16>, Changed<u16>, Added<u32>)>,
_generic_tuple: (With<T>, With<P>),
_without: Without<Option<u16>>,
_tp: PhantomData<(T, P)>,
}
fn print_nums_readonly(query: Query<NumQuery<u64, i64>, NumQueryFilter<u64, i64>>) {
for num in query.iter() {
println!("{:#?}", num);
}
}
#[derive(WorldQuery)]
#[world_query(mutable, derive(Debug))]
struct MutNumQuery<'w, T: Component, P: Component> {
i_16: &'w mut i16,
i_32_opt: Option<&'w mut i32>,
}
fn print_nums(mut query: Query<MutNumQuery, NumQueryFilter<u64, i64>>) {
for num in query.iter_mut() {
println!("{:#?}", num);
}
}
```
## TODOs:
- [x] Add support for `&T` and `&mut T`
- [x] Test
- [x] Add support for optional types
- [x] Test
- [x] Add support for `Entity`
- [x] Test
- [x] Add support for nested `WorldQuery`
- [x] Test
- [x] Add support for tuples
- [x] Test
- [x] Add support for generics
- [x] Test
- [x] Add support for query filters
- [x] Test
- [x] Add support for `PhantomData`
- [x] Test
- [x] Refactor `read_world_query_field_type_info`
- [x] Properly document `readonly` attribute for nested queries and the static assertions that guarantee safety
- [x] Test that we never implement `ReadOnlyFetch` for types that need mutable access
- [x] Test that we insert static assertions for nested `WorldQuery` that a user marked as readonly
This PR makes a number of changes to how meshes and vertex attributes are handled, which the goal of enabling easy and flexible custom vertex attributes:
* Reworks the `Mesh` type to use the newly added `VertexAttribute` internally
* `VertexAttribute` defines the name, a unique `VertexAttributeId`, and a `VertexFormat`
* `VertexAttributeId` is used to produce consistent sort orders for vertex buffer generation, replacing the more expensive and often surprising "name based sorting"
* Meshes can be used to generate a `MeshVertexBufferLayout`, which defines the layout of the gpu buffer produced by the mesh. `MeshVertexBufferLayouts` can then be used to generate actual `VertexBufferLayouts` according to the requirements of a specific pipeline. This decoupling of "mesh layout" vs "pipeline vertex buffer layout" is what enables custom attributes. We don't need to standardize _mesh layouts_ or contort meshes to meet the needs of a specific pipeline. As long as the mesh has what the pipeline needs, it will work transparently.
* Mesh-based pipelines now specialize on `&MeshVertexBufferLayout` via the new `SpecializedMeshPipeline` trait (which behaves like `SpecializedPipeline`, but adds `&MeshVertexBufferLayout`). The integrity of the pipeline cache is maintained because the `MeshVertexBufferLayout` is treated as part of the key (which is fully abstracted from implementers of the trait ... no need to add any additional info to the specialization key).
* Hashing `MeshVertexBufferLayout` is too expensive to do for every entity, every frame. To make this scalable, I added a generalized "pre-hashing" solution to `bevy_utils`: `Hashed<T>` keys and `PreHashMap<K, V>` (which uses `Hashed<T>` internally) . Why didn't I just do the quick and dirty in-place "pre-compute hash and use that u64 as a key in a hashmap" that we've done in the past? Because its wrong! Hashes by themselves aren't enough because two different values can produce the same hash. Re-hashing a hash is even worse! I decided to build a generalized solution because this pattern has come up in the past and we've chosen to do the wrong thing. Now we can do the right thing! This did unfortunately require pulling in `hashbrown` and using that in `bevy_utils`, because avoiding re-hashes requires the `raw_entry_mut` api, which isn't stabilized yet (and may never be ... `entry_ref` has favor now, but also isn't available yet). If std's HashMap ever provides the tools we need, we can move back to that. Note that adding `hashbrown` doesn't increase our dependency count because it was already in our tree. I will probably break these changes out into their own PR.
* Specializing on `MeshVertexBufferLayout` has one non-obvious behavior: it can produce identical pipelines for two different MeshVertexBufferLayouts. To optimize the number of active pipelines / reduce re-binds while drawing, I de-duplicate pipelines post-specialization using the final `VertexBufferLayout` as the key. For example, consider a pipeline that needs the layout `(position, normal)` and is specialized using two meshes: `(position, normal, uv)` and `(position, normal, other_vec2)`. If both of these meshes result in `(position, normal)` specializations, we can use the same pipeline! Now we do. Cool!
To briefly illustrate, this is what the relevant section of `MeshPipeline`'s specialization code looks like now:
```rust
impl SpecializedMeshPipeline for MeshPipeline {
type Key = MeshPipelineKey;
fn specialize(
&self,
key: Self::Key,
layout: &MeshVertexBufferLayout,
) -> RenderPipelineDescriptor {
let mut vertex_attributes = vec![
Mesh::ATTRIBUTE_POSITION.at_shader_location(0),
Mesh::ATTRIBUTE_NORMAL.at_shader_location(1),
Mesh::ATTRIBUTE_UV_0.at_shader_location(2),
];
let mut shader_defs = Vec::new();
if layout.contains(Mesh::ATTRIBUTE_TANGENT) {
shader_defs.push(String::from("VERTEX_TANGENTS"));
vertex_attributes.push(Mesh::ATTRIBUTE_TANGENT.at_shader_location(3));
}
let vertex_buffer_layout = layout
.get_layout(&vertex_attributes)
.expect("Mesh is missing a vertex attribute");
```
Notice that this is _much_ simpler than it was before. And now any mesh with any layout can be used with this pipeline, provided it has vertex postions, normals, and uvs. We even got to remove `HAS_TANGENTS` from MeshPipelineKey and `has_tangents` from `GpuMesh`, because that information is redundant with `MeshVertexBufferLayout`.
This is still a draft because I still need to:
* Add more docs
* Experiment with adding error handling to mesh pipeline specialization (which would print errors at runtime when a mesh is missing a vertex attribute required by a pipeline). If it doesn't tank perf, we'll keep it.
* Consider breaking out the PreHash / hashbrown changes into a separate PR.
* Add an example illustrating this change
* Verify that the "mesh-specialized pipeline de-duplication code" works properly
Please dont yell at me for not doing these things yet :) Just trying to get this in peoples' hands asap.
Alternative to #3120Fixes#3030
Co-authored-by: Carter Anderson <mcanders1@gmail.com>
# Objective
`all_tuples` panics when the start count is set to anything other than 0 or 1. Fix this bug.
## Solution
Originally part of #2381, this PR fixes the slice indexing used by the proc macro.
# Objective
- Fixes#4005
## Solution
- Include the `near` and `far` clipping values from the perspective projection in the `Camera` struct; before that, they were both being defaulted to 0.
# Context
I wanted to add a `texture` to my `ColorMaterial` without explicitly adding a `color`. To do this I used `..Default::default()` which in turn gave me unexpected results. I was expecting that my texture would render without any color modifications, but to my surprise it got rendered in a purple tint (`Color::rgb(1.0, 0.0, 1.0)`). To fix this I had to explicitly define the `color` using `color: Color::WHITE`.
## What I wanted to use
```rust
commands
.spawn_bundle(MaterialMesh2dBundle {
mesh: mesh_handle.clone().into(),
transform: Transform::default().with_scale(Vec3::splat(8.)),
material: materials.add(ColorMaterial {
texture: Some(texture_handle.clone()),
..Default::default() // here
}),
..Default::default()
})
```
## What I had to use instead
```rust
commands
.spawn_bundle(MaterialMesh2dBundle {
mesh: mesh_handle.clone().into(),
transform: Transform::default().with_scale(Vec3::splat(8.)),
material: materials.add(ColorMaterial {
texture: Some(texture_handle.clone()),
color: Color::WHITE, // here
}),
..Default::default()
})
```
Adds "hot reloading" of internal assets, which is normally not possible because they are loaded using `include_str` / direct Asset collection access.
This is accomplished via the following:
* Add a new `debug_asset_server` feature flag
* When that feature flag is enabled, create a second App with a second AssetServer that points to a configured location (by default the `crates` folder). Plugins that want to add hot reloading support for their assets can call the new `app.add_debug_asset::<T>()` and `app.init_debug_asset_loader::<T>()` functions.
* Load "internal" assets using the new `load_internal_asset` macro. By default this is identical to the current "include_str + register in asset collection" approach. But if the `debug_asset_server` feature flag is enabled, it will also load the asset dynamically in the debug asset server using the file path. It will then set up a correlation between the "debug asset" and the "actual asset" by listening for asset change events.
This is an alternative to #3673. The goal was to keep the boilerplate and features flags to a minimum for bevy plugin authors, and allow them to home their shaders near relevant code.
This is a draft because I haven't done _any_ quality control on this yet. I'll probably rename things and remove a bunch of unwraps. I just got it working and wanted to use it to start a conversation.
Fixes#3660
This enables shaders to (optionally) define their import path inside their source. This has a number of benefits:
1. enables users to define their own custom paths directly in their assets
2. moves the import path "close" to the asset instead of centralized in the plugin definition, which seems "better" to me.
3. makes "internal hot shader reloading" way more reasonable (see #3966)
4. logically opens the door to importing "parts" of a shader by defining "import_path blocks".
```rust
#define_import_path bevy_pbr::mesh_struct
struct Mesh {
model: mat4x4<f32>;
inverse_transpose_model: mat4x4<f32>;
// 'flags' is a bit field indicating various options. u32 is 32 bits so we have up to 32 options.
flags: u32;
};
let MESH_FLAGS_SHADOW_RECEIVER_BIT: u32 = 1u;
```
For some keys, it is too expensive to hash them on every lookup. Historically in Bevy, we have regrettably done the "wrong" thing in these cases (pre-computing hashes, then re-hashing them) because Rust's built in hashed collections don't give us the tools we need to do otherwise. Doing this is "wrong" because two different values can result in the same hash. Hashed collections generally get around this by falling back to equality checks on hash collisions. You can't do that if the key _is_ the hash. Additionally, re-hashing a hash increase the odds of collision!
#3959 needs pre-hashing to be viable, so I decided to finally properly solve the problem. The solution involves two different changes:
1. A new generalized "pre-hashing" solution in bevy_utils: `Hashed<T>` types, which store a value alongside a pre-computed hash. And `PreHashMap<K, V>` (which uses `Hashed<T>` internally) . `PreHashMap` is just an alias for a normal HashMap that uses `Hashed<T>` as the key and a new `PassHash` implementation as the Hasher.
2. Replacing the `std::collections` re-exports in `bevy_utils` with equivalent `hashbrown` impls. Avoiding re-hashes requires the `raw_entry_mut` api, which isn't stabilized yet (and may never be ... `entry_ref` has favor now, but also isn't available yet). If std's HashMap ever provides the tools we need, we can move back to that. The latest version of `hashbrown` adds support for the `entity_ref` api, so we can move to that in preparation for an std migration, if thats the direction they seem to be going in. Note that adding hashbrown doesn't increase our dependency count because it was already in our tree.
In addition to providing these core tools, I also ported the "table identity hashing" in `bevy_ecs` to `raw_entry_mut`, which was a particularly egregious case.
The biggest outstanding case is `AssetPathId`, which stores a pre-hash. We need AssetPathId to be cheaply clone-able (and ideally Copy), but `Hashed<AssetPath>` requires ownership of the AssetPath, which makes cloning ids way more expensive. We could consider doing `Hashed<Arc<AssetPath>>`, but cloning an arc is still a non-trivial expensive that needs to be considered. I would like to handle this in a separate PR. And given that we will be re-evaluating the Bevy Assets implementation in the very near future, I'd prefer to hold off until after that conversation is concluded.
Features must be called with the crate, otherwise the following error is thrown:
> error: none of the selected packages contains these features: trace_chrome
# Objective
The `custom_material.vert` shader used by the `shader_material_glsl` example is missing a `mat4 View` in `CameraViewProj` (added in [#3885](https://github.com/bevyengine/bevy/pull/3885))
## Solution
Update the definition of `CameraViewProj`
# Objective
- `WgpuOptions` is mutated to be updated with the actual device limits and features, but this information is readily available to both the main and render worlds through the `RenderDevice` which has .limits() and .features() methods
- Information about the adapter in terms of its name, the backend in use, etc were not being exposed but have clear use cases for being used to take decisions about what rendering code to use. For example, if something works well on AMD GPUs but poorly on Intel GPUs. Or perhaps something works well in Vulkan but poorly in DX12.
## Solution
- Stop mutating `WgpuOptions `and don't insert the updated values into the main and render worlds
- Return `AdapterInfo` from `initialize_renderer` and insert it into the main and render worlds
- Use `RenderDevice` limits in the lighting code that was using `WgpuOptions.limits`.
- Renamed `WgpuOptions` to `WgpuSettings`
I wanted to try one of the new examples but it felt so clunky that I wanted to improve it.
It did make me feel like maybe some input axes abstraction like Unity has might be useful.
Also, eating cake should probably be a separate system from movement.
# Objective
- `SystemStates` rock for dealing with exclusive world access, but are hard to figure out how to use.
- Fixes#3341.
## Solution
- Clearly document how to use `SystemState`, and why they're useful as an end-user.
What is says on the tin.
This has got more to do with making `clippy` slightly more *quiet* than it does with changing anything that might greatly impact readability or performance.
that said, deriving `Default` for a couple of structs is a nice easy win
# Objective
- Support overriding wgpu features and limits that were calculated from default values or queried from the adapter/backend.
- Fixes#3686
## Solution
- Add `disabled_features: Option<wgpu::Features>` to `WgpuOptions`
- Add `constrained_limits: Option<wgpu::Limits>` to `WgpuOptions`
- After maybe obtaining updated features and limits from the adapter/backend in the case of `WgpuOptionsPriority::Functionality`, enable the `WgpuOptions` `features`, disable the `disabled_features`, and constrain the `limits` by `constrained_limits`.
- Note that constraining the limits means for `wgpu::Limits` members named `max_.*` we take the minimum of that which was configured/queried for the backend/adapter and the specified constrained limit value. This means the configured/queried value is used if the constrained limit is larger as that is as much as the device/API supports, or the constrained limit value is used if it is smaller as we are imposing an artificial constraint. For members named `min_.*` we take the maximum instead. For example, a minimum stride might be 256 but we set constrained limit value of 1024, then 1024 is the more conservative value. If the constrained limit value were 16, then 256 would be the more conservative.
On platforms like wasm (on mobile) the cursor can disappear suddenly (ex: the user releases their finger from the screen). This causes the undesirable behavior in #3752. These changes make the UI handler properly handle this case.
Fixes#3752
Alternative to #3599
# Objective
If a user attempts to `.add_render_command::<P, C>()` on a world that does not contain `DrawFunctions<P>`, the engine panics with a generic `Option::unwrap` message:
```
thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', /[redacted]/bevy/crates/bevy_render/src/render_phase/draw.rs:318:76
```
## Solution
This PR adds a panic message describing the problem:
```
thread 'main' panicked at 'DrawFunctions<outline::MeshStencil> must be added to the world as a resource before adding render commands to it', /[redacted]/bevy/crates/bevy_render/src/render_phase/draw.rs:322:17
```
# Objective
The documentation was unclear but it seemed like it was intended to _only_ flip the texture coordinates of the quad. However, it was also swapping the vertex positions, which resulted in inverted winding order so the front became a back face, and the normal was pointing into the face instead of out of it.
## Solution
- This change makes the only difference the UVs being horizontally flipped.
