Attempt to interpolate transforms in the renderer

examples/testbed/src/main.rs

@@ -120,7 +120,7 @@ async fn main() {
         game.world().insert_resource(TpsAccumulator(0.0));
         
         let mut sys = BatchedSystem::new();
-        sys.with_criteria(FixedTimestep::new(30));
+        sys.with_criteria(FixedTimestep::new(10));
         sys.with_system(spin_system);
         sys.with_system(fps_system);
 

src/math/transform.rs

@@ -85,4 +85,18 @@ impl Transform {
     pub fn rotate_z(&mut self, angle: Angle) {
         self.rotate(Quat::from_rotation_z(angle.to_radians()))
     }
+    
+    /// Performs a linear interpolation between `self` and `rhs` based on the value `alpha`.
+    ///
+    /// When `alpha` is `0.0`, the result will be equal to `self`.  When `alpha` is `1.0`, the result
+    /// will be equal to `rhs`. When `alpha` is outside of range `[0, 1]`, the result is linearly
+    /// extrapolated.
+    pub fn lerp(&self, rhs: Transform, alpha: f32) -> Self {
+        let mut res = self.clone();
+        res.translation = self.translation.lerp(rhs.translation, alpha);
+        res.rotation = self.rotation.lerp(rhs.rotation, alpha);
+        res.scale = self.scale.lerp(rhs.scale, alpha);
+        
+        res
+    }
 }

src/render/render_job.rs

@@ -2,17 +2,19 @@ use edict::EntityId;
 
 use crate::math::Transform;
 
+use super::renderer::CachedTransform;
+
 pub struct RenderJob {
     pub entity: EntityId,
     pub shader_id: u64,
     pub mesh_buffer_id: uuid::Uuid,
 
     pub transform: Transform,
-    pub last_transform: Option<Transform>, // TODO: render interpolation
+    pub last_transform: Option<CachedTransform>, // TODO: render interpolation
 }
 
 impl RenderJob {
-    pub fn new(entity: EntityId, shader_id: u64, mesh_buffer_id: uuid::Uuid, transform: Transform, last_transform: Option<Transform>) -> Self {
+    pub fn new(entity: EntityId, shader_id: u64, mesh_buffer_id: uuid::Uuid, transform: Transform, last_transform: Option<CachedTransform>) -> Self {
         Self {
             entity,
             shader_id,

src/render/renderer.rs

@@ -7,6 +7,7 @@ use std::borrow::Cow;
 use edict::query::EpochOf;
 use edict::{EntityId, Entities};
 use glam::Vec3;
+use instant::Instant;
 use tracing::{debug, warn};
 use wgpu::{BindGroup, BindGroupLayout, Limits};
 use wgpu::util::DeviceExt;
@@ -48,6 +49,13 @@ struct MeshBufferStorage {
     transform_index: TransformBufferIndices,
 }
 
+#[derive(Clone, Debug)]
+pub struct CachedTransform {
+    last_updated_at: Option<Instant>,
+    cached_at: Instant,
+    transform: Transform,
+}
+
 pub struct BasicRenderer {
     pub surface: wgpu::Surface,
     pub device: wgpu::Device,
@@ -63,6 +71,7 @@ pub struct BasicRenderer {
 
     mesh_buffers: HashMap<uuid::Uuid, MeshBufferStorage>, // TODO: clean up left over buffers from deleted entities/components
     entity_meshes: HashMap<EntityId, uuid::Uuid>,
+    entity_last_transforms: HashMap<EntityId, CachedTransform>,
 
     transform_buffers: TransformBuffers,
     transform_bind_group_layout: BindGroupLayout,
@@ -312,6 +321,7 @@ impl BasicRenderer {
             texture_bind_group_layout,
             default_texture_bind_group: default_tex_bindgroup,
             depth_buffer_texture: depth_texture,
+            entity_last_transforms: HashMap::new(),
         };
 
         // create the default pipelines
@@ -510,18 +520,77 @@ impl Renderer for BasicRenderer {
 
         let mut alive_entities = HashSet::new();
         
-        for (entity, model, model_epoch, transform) in main_world.query::<(Entities, &ModelComponent, EpochOf<ModelComponent>, &TransformComponent)>().iter() {
+        let now_inst = Instant::now();
+        
+        for (entity, model, model_epoch, transform, transform_epoch) in main_world.query::<(Entities, &ModelComponent, EpochOf<ModelComponent>, &TransformComponent, EpochOf<TransformComponent>)>().iter() {
             alive_entities.insert(entity);
 
             let model = model.data.as_ref().unwrap().as_ref();
 
             for mesh in model.meshes.iter() {
+                let last_transform = self.entity_last_transforms.get(&entity).cloned();
+                
+                
+                if last_transform.is_none() {
+                    let cached = CachedTransform {
+                        last_updated_at: None,
+                        cached_at: now_inst,
+                        transform: transform.transform,
+                    };
+                    self.entity_last_transforms.insert(entity, cached);
+                } else if transform_epoch == last_epoch {
+                    let last = self.entity_last_transforms.get_mut(&entity).unwrap();
+                    last.transform = transform.transform;
+                    last.last_updated_at = Some(last.cached_at);
+                    last.cached_at = now_inst;
+                    debug!("Updated transform");
+                    // to get the fixed delta time, you'd just subtract last_updated_at and cached_at.
+                    // to get the tps_accumulator, you'd get the elapsed ms of cached_at.
+                }
+                
+                let transform_val = match last_transform {
+                    Some(last) => {
+                        debug!("now: {:?}, cached_at: {:?}, last_updated_at: {:?}", now_inst, last.cached_at, last.last_updated_at);
+                        let fixed_time = match last.last_updated_at {
+                            Some(last_updated_at) => last.cached_at - last_updated_at,
+                            None => now_inst - last.cached_at
+                        }.as_secs_f32();
+                        let accumulator = last.cached_at.elapsed().as_secs_f32();
+                        
+                        let alpha = accumulator / fixed_time;
+
+                        debug!("fixed time: {fixed_time}, acc: {accumulator}, alpha: {alpha}");
+
+                        last.transform.lerp(transform.transform, alpha)
+                    } ,
+                    None => {
+                        transform.transform
+                    }
+                };
+                
+                /*{
+                    match self.entity_last_transforms.get_mut(&entity) {
+                        Some(last) => {
+                            last.transform = transform.transform.clone();
+                            last.last_updated_at = Some(last.cached_at);
+                            last.cached_at = Instant::now();
+                        },
+                        None => {
+                            self.entity_last_transforms.insert(entity, CachedTransform {
+                                last_updated_at: None,
+                                cached_at: Instant::now(),
+                                transform: transform.transform.clone(),
+                            });
+                        }
+                    }
+                }*/
+                
                 if !self.process_mesh(entity, transform.transform, mesh) && model_epoch == last_epoch {
                     self.update_mesh_buffers(entity, mesh);
                 }
                 
                 let shader = mesh.material().shader_uuid.unwrap_or(0);
-                let job = RenderJob::new(entity, shader, mesh.uuid, transform.transform, None);
+                let job = RenderJob::new(entity, shader, mesh.uuid, transform_val, None);
                 self.render_jobs.push_back(job);
             }
         }