1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
use crate::render_phase::{PhaseItem, TrackedRenderPass};
use bevy_app::{App, SubApp};
use bevy_ecs::{
    entity::Entity,
    query::{QueryState, ROQueryItem, ReadOnlyQueryData},
    system::{ReadOnlySystemParam, Resource, SystemParam, SystemParamItem, SystemState},
    world::World,
};
use bevy_utils::{all_tuples, TypeIdMap};
use std::{
    any::TypeId,
    fmt::Debug,
    hash::Hash,
    sync::{PoisonError, RwLock, RwLockReadGuard, RwLockWriteGuard},
};

/// A draw function used to draw [`PhaseItem`]s.
///
/// The draw function can retrieve and query the required ECS data from the render world.
///
/// This trait can either be implemented directly or implicitly composed out of multiple modular
/// [`RenderCommand`]s. For more details and an example see the [`RenderCommand`] documentation.
pub trait Draw<P: PhaseItem>: Send + Sync + 'static {
    /// Prepares the draw function to be used. This is called once and only once before the phase
    /// begins. There may be zero or more [`draw`](Draw::draw) calls following a call to this function.
    /// Implementing this is optional.
    #[allow(unused_variables)]
    fn prepare(&mut self, world: &'_ World) {}

    /// Draws a [`PhaseItem`] by issuing zero or more `draw` calls via the [`TrackedRenderPass`].
    fn draw<'w>(
        &mut self,
        world: &'w World,
        pass: &mut TrackedRenderPass<'w>,
        view: Entity,
        item: &P,
    );
}

// TODO: make this generic?
/// An identifier for a [`Draw`] function stored in [`DrawFunctions`].
#[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, Hash)]
pub struct DrawFunctionId(u32);

/// Stores all [`Draw`] functions for the [`PhaseItem`] type.
///
/// For retrieval, the [`Draw`] functions are mapped to their respective [`TypeId`]s.
pub struct DrawFunctionsInternal<P: PhaseItem> {
    pub draw_functions: Vec<Box<dyn Draw<P>>>,
    pub indices: TypeIdMap<DrawFunctionId>,
}

impl<P: PhaseItem> DrawFunctionsInternal<P> {
    /// Prepares all draw function. This is called once and only once before the phase begins.
    pub fn prepare(&mut self, world: &World) {
        for function in &mut self.draw_functions {
            function.prepare(world);
        }
    }

    /// Adds the [`Draw`] function and maps it to its own type.
    pub fn add<T: Draw<P>>(&mut self, draw_function: T) -> DrawFunctionId {
        self.add_with::<T, T>(draw_function)
    }

    /// Adds the [`Draw`] function and maps it to the type `T`
    pub fn add_with<T: 'static, D: Draw<P>>(&mut self, draw_function: D) -> DrawFunctionId {
        let id = DrawFunctionId(self.draw_functions.len().try_into().unwrap());
        self.draw_functions.push(Box::new(draw_function));
        self.indices.insert(TypeId::of::<T>(), id);
        id
    }

    /// Retrieves the [`Draw`] function corresponding to the `id` mutably.
    pub fn get_mut(&mut self, id: DrawFunctionId) -> Option<&mut dyn Draw<P>> {
        self.draw_functions.get_mut(id.0 as usize).map(|f| &mut **f)
    }

    /// Retrieves the id of the [`Draw`] function corresponding to their associated type `T`.
    pub fn get_id<T: 'static>(&self) -> Option<DrawFunctionId> {
        self.indices.get(&TypeId::of::<T>()).copied()
    }

    /// Retrieves the id of the [`Draw`] function corresponding to their associated type `T`.
    ///
    /// Fallible wrapper for [`Self::get_id()`]
    ///
    /// ## Panics
    /// If the id doesn't exist, this function will panic.
    pub fn id<T: 'static>(&self) -> DrawFunctionId {
        self.get_id::<T>().unwrap_or_else(|| {
            panic!(
                "Draw function {} not found for {}",
                std::any::type_name::<T>(),
                std::any::type_name::<P>()
            )
        })
    }
}

/// Stores all draw functions for the [`PhaseItem`] type hidden behind a reader-writer lock.
///
/// To access them the [`DrawFunctions::read`] and [`DrawFunctions::write`] methods are used.
#[derive(Resource)]
pub struct DrawFunctions<P: PhaseItem> {
    internal: RwLock<DrawFunctionsInternal<P>>,
}

impl<P: PhaseItem> Default for DrawFunctions<P> {
    fn default() -> Self {
        Self {
            internal: RwLock::new(DrawFunctionsInternal {
                draw_functions: Vec::new(),
                indices: Default::default(),
            }),
        }
    }
}

impl<P: PhaseItem> DrawFunctions<P> {
    /// Accesses the draw functions in read mode.
    pub fn read(&self) -> RwLockReadGuard<'_, DrawFunctionsInternal<P>> {
        self.internal.read().unwrap_or_else(PoisonError::into_inner)
    }

    /// Accesses the draw functions in write mode.
    pub fn write(&self) -> RwLockWriteGuard<'_, DrawFunctionsInternal<P>> {
        self.internal
            .write()
            .unwrap_or_else(PoisonError::into_inner)
    }
}

/// [`RenderCommand`]s are modular standardized pieces of render logic that can be composed into
/// [`Draw`] functions.
///
/// To turn a stateless render command into a usable draw function it has to be wrapped by a
/// [`RenderCommandState`].
/// This is done automatically when registering a render command as a [`Draw`] function via the
/// [`AddRenderCommand::add_render_command`] method.
///
/// Compared to the draw function the required ECS data is fetched automatically
/// (by the [`RenderCommandState`]) from the render world.
/// Therefore the three types [`Param`](RenderCommand::Param),
/// [`ViewQuery`](RenderCommand::ViewQuery) and
/// [`ItemQuery`](RenderCommand::ItemQuery) are used.
/// They specify which information is required to execute the render command.
///
/// Multiple render commands can be combined together by wrapping them in a tuple.
///
/// # Example
///
/// The `DrawMaterial` draw function is created from the following render command
/// tuple. Const generics are used to set specific bind group locations:
///
/// ```
/// # use bevy_render::render_phase::SetItemPipeline;
/// # struct SetMeshViewBindGroup<const N: usize>;
/// # struct SetMeshBindGroup<const N: usize>;
/// # struct SetMaterialBindGroup<M, const N: usize>(core::marker::PhantomData<M>);
/// # struct DrawMesh;
/// pub type DrawMaterial<M> = (
///     SetItemPipeline,
///     SetMeshViewBindGroup<0>,
///     SetMeshBindGroup<1>,
///     SetMaterialBindGroup<M, 2>,
///     DrawMesh,
/// );
/// ```
pub trait RenderCommand<P: PhaseItem> {
    /// Specifies the general ECS data (e.g. resources) required by [`RenderCommand::render`].
    ///
    /// When fetching resources, note that, due to lifetime limitations of the `Deref` trait,
    /// [`SRes::into_inner`] must be called on each [`SRes`] reference in the
    /// [`RenderCommand::render`] method, instead of being automatically dereferenced as is the
    /// case in normal `systems`.
    ///
    /// All parameters have to be read only.
    ///
    /// [`SRes`]: bevy_ecs::system::lifetimeless::SRes
    /// [`SRes::into_inner`]: bevy_ecs::system::lifetimeless::SRes::into_inner
    type Param: SystemParam + 'static;
    /// Specifies the ECS data of the view entity required by [`RenderCommand::render`].
    ///
    /// The view entity refers to the camera, or shadow-casting light, etc. from which the phase
    /// item will be rendered from.
    /// All components have to be accessed read only.
    type ViewQuery: ReadOnlyQueryData;
    /// Specifies the ECS data of the item entity required by [`RenderCommand::render`].
    ///
    /// The item is the entity that will be rendered for the corresponding view.
    /// All components have to be accessed read only.
    ///
    /// For efficiency reasons, Bevy doesn't always extract entities to the
    /// render world; for instance, entities that simply consist of meshes are
    /// often not extracted. If the entity doesn't exist in the render world,
    /// the supplied query data will be `None`.
    type ItemQuery: ReadOnlyQueryData;

    /// Renders a [`PhaseItem`] by recording commands (e.g. setting pipelines, binding bind groups,
    /// issuing draw calls, etc.) via the [`TrackedRenderPass`].
    fn render<'w>(
        item: &P,
        view: ROQueryItem<'w, Self::ViewQuery>,
        entity: Option<ROQueryItem<'w, Self::ItemQuery>>,
        param: SystemParamItem<'w, '_, Self::Param>,
        pass: &mut TrackedRenderPass<'w>,
    ) -> RenderCommandResult;
}

/// The result of a [`RenderCommand`].
#[derive(Debug)]
pub enum RenderCommandResult {
    Success,
    Failure,
}

macro_rules! render_command_tuple_impl {
    ($(($name: ident, $view: ident, $entity: ident)),*) => {
        impl<P: PhaseItem, $($name: RenderCommand<P>),*> RenderCommand<P> for ($($name,)*) {
            type Param = ($($name::Param,)*);
            type ViewQuery = ($($name::ViewQuery,)*);
            type ItemQuery = ($($name::ItemQuery,)*);

            #[allow(non_snake_case)]
            fn render<'w>(
                _item: &P,
                ($($view,)*): ROQueryItem<'w, Self::ViewQuery>,
                maybe_entities: Option<ROQueryItem<'w, Self::ItemQuery>>,
                ($($name,)*): SystemParamItem<'w, '_, Self::Param>,
                _pass: &mut TrackedRenderPass<'w>,
            ) -> RenderCommandResult {
                match maybe_entities {
                    None => {
                        $(if let RenderCommandResult::Failure = $name::render(_item, $view, None, $name, _pass) {
                            return RenderCommandResult::Failure;
                        })*
                    }
                    Some(($($entity,)*)) => {
                        $(if let RenderCommandResult::Failure = $name::render(_item, $view, Some($entity), $name, _pass) {
                            return RenderCommandResult::Failure;
                        })*
                    }
                }
                RenderCommandResult::Success
            }
        }
    };
}

all_tuples!(render_command_tuple_impl, 0, 15, C, V, E);

/// Wraps a [`RenderCommand`] into a state so that it can be used as a [`Draw`] function.
///
/// The [`RenderCommand::Param`], [`RenderCommand::ViewQuery`] and
/// [`RenderCommand::ItemQuery`] are fetched from the ECS and passed to the command.
pub struct RenderCommandState<P: PhaseItem + 'static, C: RenderCommand<P>> {
    state: SystemState<C::Param>,
    view: QueryState<C::ViewQuery>,
    entity: QueryState<C::ItemQuery>,
}

impl<P: PhaseItem, C: RenderCommand<P>> RenderCommandState<P, C> {
    /// Creates a new [`RenderCommandState`] for the [`RenderCommand`].
    pub fn new(world: &mut World) -> Self {
        Self {
            state: SystemState::new(world),
            view: world.query(),
            entity: world.query(),
        }
    }
}

impl<P: PhaseItem, C: RenderCommand<P> + Send + Sync + 'static> Draw<P> for RenderCommandState<P, C>
where
    C::Param: ReadOnlySystemParam,
{
    /// Prepares the render command to be used. This is called once and only once before the phase
    /// begins. There may be zero or more [`draw`](RenderCommandState::draw) calls following a call to this function.
    fn prepare(&mut self, world: &'_ World) {
        self.state.update_archetypes(world);
        self.view.update_archetypes(world);
        self.entity.update_archetypes(world);
    }

    /// Fetches the ECS parameters for the wrapped [`RenderCommand`] and then renders it.
    fn draw<'w>(
        &mut self,
        world: &'w World,
        pass: &mut TrackedRenderPass<'w>,
        view: Entity,
        item: &P,
    ) {
        let param = self.state.get_manual(world);
        let view = self.view.get_manual(world, view).unwrap();
        let entity = self.entity.get_manual(world, item.entity()).ok();
        // TODO: handle/log `RenderCommand` failure
        C::render(item, view, entity, param, pass);
    }
}

/// Registers a [`RenderCommand`] as a [`Draw`] function.
/// They are stored inside the [`DrawFunctions`] resource of the app.
pub trait AddRenderCommand {
    /// Adds the [`RenderCommand`] for the specified render phase to the app.
    fn add_render_command<P: PhaseItem, C: RenderCommand<P> + Send + Sync + 'static>(
        &mut self,
    ) -> &mut Self
    where
        C::Param: ReadOnlySystemParam;
}

impl AddRenderCommand for SubApp {
    fn add_render_command<P: PhaseItem, C: RenderCommand<P> + Send + Sync + 'static>(
        &mut self,
    ) -> &mut Self
    where
        C::Param: ReadOnlySystemParam,
    {
        let draw_function = RenderCommandState::<P, C>::new(self.world_mut());
        let draw_functions = self
            .world()
            .get_resource::<DrawFunctions<P>>()
            .unwrap_or_else(|| {
                panic!(
                    "DrawFunctions<{}> must be added to the world as a resource \
                     before adding render commands to it",
                    std::any::type_name::<P>(),
                );
            });
        draw_functions.write().add_with::<C, _>(draw_function);
        self
    }
}

impl AddRenderCommand for App {
    fn add_render_command<P: PhaseItem, C: RenderCommand<P> + Send + Sync + 'static>(
        &mut self,
    ) -> &mut Self
    where
        C::Param: ReadOnlySystemParam,
    {
        SubApp::add_render_command::<P, C>(self.main_mut());
        self
    }
}