From b897dc312e46ddb17ab0433666f3b609e5d0df19 Mon Sep 17 00:00:00 2001
From: awtterpip <zach.spams0508@gmail.com>
Date: Thu, 14 Mar 2024 18:00:56 -0500
Subject: [PATCH] fix projection

---
 crates/bevy_xr/src/camera.rs | 45 +++++++++++++++++++++++++++++-------
 1 file changed, 37 insertions(+), 8 deletions(-)

diff --git a/crates/bevy_xr/src/camera.rs b/crates/bevy_xr/src/camera.rs
index 5ffde09..913262b 100644
--- a/crates/bevy_xr/src/camera.rs
+++ b/crates/bevy_xr/src/camera.rs
@@ -1,41 +1,50 @@
-use bevy::app::{App, Plugin};
+use bevy::app::{App, Plugin, PostUpdate};
 use bevy::core_pipeline::core_3d::graph::Core3d;
 use bevy::core_pipeline::core_3d::Camera3d;
 use bevy::core_pipeline::tonemapping::{DebandDither, Tonemapping};
 use bevy::ecs::bundle::Bundle;
 use bevy::ecs::component::Component;
 use bevy::ecs::reflect::ReflectComponent;
+use bevy::ecs::schedule::IntoSystemConfigs;
 use bevy::math::{Mat4, Vec3A};
+use bevy::reflect::std_traits::ReflectDefault;
 use bevy::reflect::Reflect;
 use bevy::render::camera::{
     Camera, CameraMainTextureUsages, CameraProjection, CameraProjectionPlugin, CameraRenderGraph,
     Exposure,
 };
+use bevy::render::extract_component::{ExtractComponent, ExtractComponentPlugin};
 use bevy::render::primitives::Frustum;
-use bevy::render::view::{ColorGrading, VisibleEntities};
+use bevy::render::view::{update_frusta, ColorGrading, VisibilitySystems, VisibleEntities};
 use bevy::transform::components::{GlobalTransform, Transform};
+use bevy::transform::TransformSystem;
 
 pub struct XrCameraPlugin;
 
 impl Plugin for XrCameraPlugin {
     fn build(&self, app: &mut App) {
         app.add_plugins(CameraProjectionPlugin::<XrProjection>::default());
+        app.add_systems(
+            PostUpdate,
+            update_frusta::<XrProjection>
+                .after(TransformSystem::TransformPropagate)
+                .before(VisibilitySystems::UpdatePerspectiveFrusta),
+        );
+        app.add_plugins(ExtractComponentPlugin::<XrProjection>::default());
     }
 }
 
-#[derive(Clone, Copy, Component, Reflect, Debug)]
-#[reflect(Component)]
+#[derive(Debug, Clone, Component, Reflect, ExtractComponent)]
+#[reflect(Component, Default)]
 pub struct XrProjection {
     pub projection_matrix: Mat4,
     pub near: f32,
-    pub far: f32,
 }
 
 impl Default for XrProjection {
     fn default() -> Self {
         Self {
             near: 0.1,
-            far: 1000.,
             projection_matrix: Mat4::IDENTITY,
         }
     }
@@ -53,12 +62,32 @@ impl CameraProjection for XrProjection {
     fn update(&mut self, _width: f32, _height: f32) {}
 
     fn far(&self) -> f32 {
-        self.far
+        let far = self.projection_matrix.to_cols_array()[14]
+            / (self.projection_matrix.to_cols_array()[10] + 1.0);
+
+        far
     }
 
     // TODO calculate this properly
     fn get_frustum_corners(&self, _z_near: f32, _z_far: f32) -> [Vec3A; 8] {
-        Default::default()
+        let ndc_corners = [
+            Vec3A::new(1.0, -1.0, 1.0),   // Bottom-right far
+            Vec3A::new(1.0, 1.0, 1.0),    // Top-right far
+            Vec3A::new(-1.0, 1.0, 1.0),   // Top-left far
+            Vec3A::new(-1.0, -1.0, 1.0),  // Bottom-left far
+            Vec3A::new(1.0, -1.0, -1.0),  // Bottom-right near
+            Vec3A::new(1.0, 1.0, -1.0),   // Top-right near
+            Vec3A::new(-1.0, 1.0, -1.0),  // Top-left near
+            Vec3A::new(-1.0, -1.0, -1.0), // Bottom-left near
+        ];
+
+        let mut view_space_corners = [Vec3A::ZERO; 8];
+        let inverse_matrix = self.projection_matrix.inverse();
+        for (i, corner) in ndc_corners.into_iter().enumerate() {
+            view_space_corners[i] = inverse_matrix.transform_point3a(corner);
+        }
+
+        view_space_corners
     }
 }