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//! The modular rendering abstraction responsible for queuing, preparing, sorting and drawing
//! entities as part of separate render phases.
//!
//! In Bevy each view (camera, or shadow-casting light, etc.) has one or multiple [`RenderPhase`]s
//! (e.g. opaque, transparent, shadow, etc).
//! They are used to queue entities for rendering.
//! Multiple phases might be required due to different sorting/batching behaviours
//! (e.g. opaque: front to back, transparent: back to front) or because one phase depends on
//! the rendered texture of the previous phase (e.g. for screen-space reflections).
//!
//! To draw an entity, a corresponding [`PhaseItem`] has to be added to one or multiple of these
//! render phases for each view that it is visible in.
//! This must be done in the [`RenderSet::Queue`](crate::RenderSet::Queue).
//! After that the render phase sorts them in the
//! [`RenderSet::PhaseSort`](crate::RenderSet::PhaseSort).
//! Finally the items are rendered using a single [`TrackedRenderPass`], during the
//! [`RenderSet::Render`](crate::RenderSet::Render).
//!
//! Therefore each phase item is assigned a [`Draw`] function.
//! These set up the state of the [`TrackedRenderPass`] (i.e. select the
//! [`RenderPipeline`](crate::render_resource::RenderPipeline), configure the
//! [`BindGroup`](crate::render_resource::BindGroup)s, etc.) and then issue a draw call,
//! for the corresponding item.
//!
//! The [`Draw`] function trait can either be implemented directly or such a function can be
//! created by composing multiple [`RenderCommand`]s.
mod draw;
mod draw_state;
mod rangefinder;
pub use draw::*;
pub use draw_state::*;
pub use rangefinder::*;
use crate::render_resource::{CachedRenderPipelineId, PipelineCache};
use bevy_ecs::{
prelude::*,
system::{lifetimeless::SRes, SystemParamItem},
};
use std::ops::Range;
/// A collection of all rendering instructions, that will be executed by the GPU, for a
/// single render phase for a single view.
///
/// Each view (camera, or shadow-casting light, etc.) can have one or multiple render phases.
/// They are used to queue entities for rendering.
/// Multiple phases might be required due to different sorting/batching behaviours
/// (e.g. opaque: front to back, transparent: back to front) or because one phase depends on
/// the rendered texture of the previous phase (e.g. for screen-space reflections).
/// All [`PhaseItem`]s are then rendered using a single [`TrackedRenderPass`].
/// The render pass might be reused for multiple phases to reduce GPU overhead.
#[derive(Component)]
pub struct RenderPhase<I: PhaseItem> {
pub items: Vec<I>,
}
impl<I: PhaseItem> Default for RenderPhase<I> {
fn default() -> Self {
Self { items: Vec::new() }
}
}
impl<I: PhaseItem> RenderPhase<I> {
/// Adds a [`PhaseItem`] to this render phase.
#[inline]
pub fn add(&mut self, item: I) {
self.items.push(item);
}
/// Sorts all of its [`PhaseItem`]s.
pub fn sort(&mut self) {
I::sort(&mut self.items);
}
/// Renders all of its [`PhaseItem`]s using their corresponding draw functions.
pub fn render<'w>(
&self,
render_pass: &mut TrackedRenderPass<'w>,
world: &'w World,
view: Entity,
) {
let draw_functions = world.resource::<DrawFunctions<I>>();
let mut draw_functions = draw_functions.write();
draw_functions.prepare(world);
for item in &self.items {
let draw_function = draw_functions.get_mut(item.draw_function()).unwrap();
draw_function.draw(world, render_pass, view, item);
}
}
}
impl<I: BatchedPhaseItem> RenderPhase<I> {
/// Batches the compatible [`BatchedPhaseItem`]s of this render phase
pub fn batch(&mut self) {
// TODO: this could be done in-place
let mut items = std::mem::take(&mut self.items).into_iter();
self.items.reserve(items.len());
// Start the first batch from the first item
if let Some(mut current_batch) = items.next() {
// Batch following items until we find an incompatible item
for next_item in items {
if matches!(
current_batch.add_to_batch(&next_item),
BatchResult::IncompatibleItems
) {
// Store the completed batch, and start a new one from the incompatible item
self.items.push(current_batch);
current_batch = next_item;
}
}
// Store the last batch
self.items.push(current_batch);
}
}
}
/// An item (entity of the render world) which will be drawn to a texture or the screen,
/// as part of a [`RenderPhase`].
///
/// The data required for rendering an entity is extracted from the main world in the
/// [`ExtractSchedule`](crate::ExtractSchedule).
/// Then it has to be queued up for rendering during the
/// [`RenderSet::Queue`](crate::RenderSet::Queue), by adding a corresponding phase item to
/// a render phase.
/// Afterwards it will be sorted and rendered automatically in the
/// [`RenderSet::PhaseSort`](crate::RenderSet::PhaseSort) and
/// [`RenderSet::Render`](crate::RenderSet::Render), respectively.
pub trait PhaseItem: Sized + Send + Sync + 'static {
/// The type used for ordering the items. The smallest values are drawn first.
/// This order can be calculated using the [`ViewRangefinder3d`],
/// based on the view-space `Z` value of the corresponding view matrix.
type SortKey: Ord;
/// The corresponding entity that will be drawn.
///
/// This is used to fetch the render data of the entity, required by the draw function,
/// from the render world .
fn entity(&self) -> Entity;
/// Determines the order in which the items are drawn.
fn sort_key(&self) -> Self::SortKey;
/// Specifies the [`Draw`] function used to render the item.
fn draw_function(&self) -> DrawFunctionId;
/// Sorts a slice of phase items into render order. Generally if the same type
/// implements [`BatchedPhaseItem`], this should use a stable sort like [`slice::sort_by_key`].
/// In almost all other cases, this should not be altered from the default,
/// which uses a unstable sort, as this provides the best balance of CPU and GPU
/// performance.
///
/// Implementers can optionally not sort the list at all. This is generally advisable if and
/// only if the renderer supports a depth prepass, which is by default not supported by
/// the rest of Bevy's first party rendering crates. Even then, this may have a negative
/// impact on GPU-side performance due to overdraw.
///
/// It's advised to always profile for performance changes when changing this implementation.
#[inline]
fn sort(items: &mut [Self]) {
items.sort_unstable_by_key(|item| item.sort_key());
}
}
/// A [`PhaseItem`] item, that automatically sets the appropriate render pipeline,
/// cached in the [`PipelineCache`].
///
/// You can use the [`SetItemPipeline`] render command to set the pipeline for this item.
pub trait CachedRenderPipelinePhaseItem: PhaseItem {
/// The id of the render pipeline, cached in the [`PipelineCache`], that will be used to draw
/// this phase item.
fn cached_pipeline(&self) -> CachedRenderPipelineId;
}
/// A [`RenderCommand`] that sets the pipeline for the [`CachedRenderPipelinePhaseItem`].
pub struct SetItemPipeline;
impl<P: CachedRenderPipelinePhaseItem> RenderCommand<P> for SetItemPipeline {
type Param = SRes<PipelineCache>;
type ViewWorldQuery = ();
type ItemWorldQuery = ();
#[inline]
fn render<'w>(
item: &P,
_view: (),
_entity: (),
pipeline_cache: SystemParamItem<'w, '_, Self::Param>,
pass: &mut TrackedRenderPass<'w>,
) -> RenderCommandResult {
if let Some(pipeline) = pipeline_cache
.into_inner()
.get_render_pipeline(item.cached_pipeline())
{
pass.set_render_pipeline(pipeline);
RenderCommandResult::Success
} else {
RenderCommandResult::Failure
}
}
}
/// A [`PhaseItem`] that can be batched dynamically.
///
/// Batching is an optimization that regroups multiple items in the same vertex buffer
/// to render them in a single draw call.
///
/// If this is implemented on a type, the implementation of [`PhaseItem::sort`] should
/// be changed to implement a stable sort, or incorrect/suboptimal batching may result.
pub trait BatchedPhaseItem: PhaseItem {
/// Range in the vertex buffer of this item.
fn batch_range(&self) -> &Option<Range<u32>>;
/// Range in the vertex buffer of this item.
fn batch_range_mut(&mut self) -> &mut Option<Range<u32>>;
/// Batches another item within this item if they are compatible.
/// Items can be batched together if they have the same entity, and consecutive ranges.
/// If batching is successful, the `other` item should be discarded from the render pass.
#[inline]
fn add_to_batch(&mut self, other: &Self) -> BatchResult {
let self_entity = self.entity();
if let (Some(self_batch_range), Some(other_batch_range)) = (
self.batch_range_mut().as_mut(),
other.batch_range().as_ref(),
) {
// If the items are compatible, join their range into `self`
if self_entity == other.entity() {
if self_batch_range.end == other_batch_range.start {
self_batch_range.end = other_batch_range.end;
return BatchResult::Success;
} else if self_batch_range.start == other_batch_range.end {
self_batch_range.start = other_batch_range.start;
return BatchResult::Success;
}
}
}
BatchResult::IncompatibleItems
}
}
/// The result of a batching operation.
pub enum BatchResult {
/// The `other` item was batched into `self`
Success,
/// `self` and `other` cannot be batched together
IncompatibleItems,
}
/// This system sorts the [`PhaseItem`]s of all [`RenderPhase`]s of this type.
pub fn sort_phase_system<I: PhaseItem>(mut render_phases: Query<&mut RenderPhase<I>>) {
for mut phase in &mut render_phases {
phase.sort();
}
}
/// This system batches the [`PhaseItem`]s of all [`RenderPhase`]s of this type.
pub fn batch_phase_system<I: BatchedPhaseItem>(mut render_phases: Query<&mut RenderPhase<I>>) {
for mut phase in &mut render_phases {
phase.batch();
}
}
#[cfg(test)]
mod tests {
use super::*;
use bevy_ecs::entity::Entity;
use std::ops::Range;
#[test]
fn batching() {
#[derive(Debug, PartialEq)]
struct TestPhaseItem {
entity: Entity,
batch_range: Option<Range<u32>>,
}
impl PhaseItem for TestPhaseItem {
type SortKey = ();
fn entity(&self) -> Entity {
self.entity
}
fn sort_key(&self) -> Self::SortKey {}
fn draw_function(&self) -> DrawFunctionId {
unimplemented!();
}
}
impl BatchedPhaseItem for TestPhaseItem {
fn batch_range(&self) -> &Option<Range<u32>> {
&self.batch_range
}
fn batch_range_mut(&mut self) -> &mut Option<Range<u32>> {
&mut self.batch_range
}
}
let mut render_phase = RenderPhase::<TestPhaseItem>::default();
let items = [
TestPhaseItem {
entity: Entity::from_raw(0),
batch_range: Some(0..5),
},
// This item should be batched
TestPhaseItem {
entity: Entity::from_raw(0),
batch_range: Some(5..10),
},
TestPhaseItem {
entity: Entity::from_raw(1),
batch_range: Some(0..5),
},
TestPhaseItem {
entity: Entity::from_raw(0),
batch_range: Some(10..15),
},
TestPhaseItem {
entity: Entity::from_raw(1),
batch_range: Some(5..10),
},
TestPhaseItem {
entity: Entity::from_raw(1),
batch_range: None,
},
TestPhaseItem {
entity: Entity::from_raw(1),
batch_range: Some(10..15),
},
TestPhaseItem {
entity: Entity::from_raw(1),
batch_range: Some(20..25),
},
// This item should be batched
TestPhaseItem {
entity: Entity::from_raw(1),
batch_range: Some(25..30),
},
// This item should be batched
TestPhaseItem {
entity: Entity::from_raw(1),
batch_range: Some(30..35),
},
];
for item in items {
render_phase.add(item);
}
render_phase.batch();
let items_batched = [
TestPhaseItem {
entity: Entity::from_raw(0),
batch_range: Some(0..10),
},
TestPhaseItem {
entity: Entity::from_raw(1),
batch_range: Some(0..5),
},
TestPhaseItem {
entity: Entity::from_raw(0),
batch_range: Some(10..15),
},
TestPhaseItem {
entity: Entity::from_raw(1),
batch_range: Some(5..10),
},
TestPhaseItem {
entity: Entity::from_raw(1),
batch_range: None,
},
TestPhaseItem {
entity: Entity::from_raw(1),
batch_range: Some(10..15),
},
TestPhaseItem {
entity: Entity::from_raw(1),
batch_range: Some(20..35),
},
];
assert_eq!(&*render_phase.items, items_batched);
}
}