From 5fac1fe0a909a7e16f9fb8944d7a8103a9676052 Mon Sep 17 00:00:00 2001
From: JMS55 <47158642+JMS55@users.noreply.github.com>
Date: Thu, 17 Aug 2023 12:46:43 -0700
Subject: [PATCH] Fix temporal jitter bug (#9462)

* Fixed jitter being applied in the wrong coordinate space, leading to
aliasing.
* Fixed incorrectly using the cached view_proj instead of account for
temporal jitter.
* Added a diagram to ensure the coordinate space is clear.

Before:

![image](https://github.com/bevyengine/bevy/assets/47158642/55b4bed4-4fb0-4fb2-a271-cc10a987e4d7)

After:

![image](https://github.com/bevyengine/bevy/assets/47158642/cbde4553-4e35-44d9-8ccf-f3a06e64a31f)
---
 crates/bevy_render/src/camera/camera.rs |  5 +++--
 crates/bevy_render/src/view/mod.rs      | 12 +++++++++---
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/crates/bevy_render/src/camera/camera.rs b/crates/bevy_render/src/camera/camera.rs
index c85e8d68cfc9d..d6aa154dc174d 100644
--- a/crates/bevy_render/src/camera/camera.rs
+++ b/crates/bevy_render/src/camera/camera.rs
@@ -19,7 +19,7 @@ use bevy_ecs::{
     system::{Commands, Query, Res, ResMut, Resource},
 };
 use bevy_log::warn;
-use bevy_math::{Mat4, Ray, Rect, URect, UVec2, UVec4, Vec2, Vec3};
+use bevy_math::{vec2, Mat4, Ray, Rect, URect, UVec2, UVec4, Vec2, Vec3};
 use bevy_reflect::prelude::*;
 use bevy_transform::components::GlobalTransform;
 use bevy_utils::{HashMap, HashSet};
@@ -806,7 +806,8 @@ impl TemporalJitter {
             return;
         }
 
-        let jitter = self.offset / view_size;
+        // https://github.com/GPUOpen-LibrariesAndSDKs/FidelityFX-SDK/blob/d7531ae47d8b36a5d4025663e731a47a38be882f/docs/techniques/media/super-resolution-temporal/jitter-space.svg
+        let jitter = (self.offset * vec2(2.0, -2.0)) / view_size;
 
         projection.z_axis.x += jitter.x;
         projection.z_axis.y += jitter.y;
diff --git a/crates/bevy_render/src/view/mod.rs b/crates/bevy_render/src/view/mod.rs
index b2b773787c6e4..9167279081b2d 100644
--- a/crates/bevy_render/src/view/mod.rs
+++ b/crates/bevy_render/src/view/mod.rs
@@ -375,11 +375,17 @@ pub fn prepare_view_uniforms(
         let view = camera.transform.compute_matrix();
         let inverse_view = view.inverse();
 
+        let view_proj = if temporal_jitter.is_some() {
+            projection * inverse_view
+        } else {
+            camera
+                .view_projection
+                .unwrap_or_else(|| projection * inverse_view)
+        };
+
         let view_uniforms = ViewUniformOffset {
             offset: view_uniforms.uniforms.push(ViewUniform {
-                view_proj: camera
-                    .view_projection
-                    .unwrap_or_else(|| projection * inverse_view),
+                view_proj,
                 unjittered_view_proj: unjittered_projection * inverse_view,
                 inverse_view_proj: view * inverse_projection,
                 view,