Fix incorrect distance given by ViewRangefinder3d

crates/bevy_render/src/render_phase/rangefinder.rs

@@ -1,34 +1,36 @@
 use bevy_math::{Mat4, Vec3, Vec4};
 
-/// A distance calculator for the draw order of [`PhaseItem`](crate::render_phase::PhaseItem)s.
+/// A depth calculator for the draw order of [`PhaseItem`](crate::render_phase::PhaseItem)s.
 pub struct ViewRangefinder3d {
-    inverse_view_row_2: Vec4,
+    view_proj_row_2: Vec4,
+    view_proj_row_3: Vec4,
 }
 
 impl ViewRangefinder3d {
-    /// Creates a 3D rangefinder for a view matrix.
-    pub fn from_view_matrix(view_matrix: &Mat4) -> ViewRangefinder3d {
-        let inverse_view_matrix = view_matrix.inverse();
-
+    /// Creates a 3D rangefinder for a view-projection matrix.
+    pub fn from_view_proj_matrix(view_proj_matrix: &Mat4) -> ViewRangefinder3d {
         ViewRangefinder3d {
-            inverse_view_row_2: inverse_view_matrix.row(2),
+            view_proj_row_2: view_proj_matrix.row(2),
+            view_proj_row_3: view_proj_matrix.row(3),
         }
     }
 
-    /// Calculates the distance, or view-space `Z` value, for the given `translation`.
+    /// Calculates the depth for the given `translation`.
     #[inline]
     pub fn distance_translation(&self, translation: &Vec3) -> f32 {
-        // NOTE: row 2 of the inverse view matrix dotted with the translation from the model matrix
-        // gives the z component of translation of the mesh in view-space
-        self.inverse_view_row_2.dot(translation.extend(1.0))
+        // NOTE: row 2 of the view-projection matrix dotted with the translation from the model matrix
+        // gives the z component of translation of the mesh in clip-space.
+        // However, as we are using an infinite projection matrix for perspective projection,
+        // this value is meaningless.
+        let position = translation.extend(1.0);
+        self.view_proj_row_2.dot(position) / self.view_proj_row_3.dot(position)
     }
 
-    /// Calculates the distance, or view-space `Z` value, for the given `transform`.
+    /// Calculates the depth for the given `transform`.
     #[inline]
     pub fn distance(&self, transform: &Mat4) -> f32 {
-        // NOTE: row 2 of the inverse view matrix dotted with column 3 of the model matrix
-        // gives the z component of translation of the mesh in view-space
-        self.inverse_view_row_2.dot(transform.col(3))
+        let position = transform.col(3);
+        self.view_proj_row_2.dot(position) / self.view_proj_row_3.dot(position)
     }
 }
 
@@ -39,8 +41,8 @@ mod tests {
 
     #[test]
     fn distance() {
-        let view_matrix = Mat4::from_translation(Vec3::new(0.0, 0.0, -1.0));
-        let rangefinder = ViewRangefinder3d::from_view_matrix(&view_matrix);
+        let view_proj_matrix = Mat4::from_translation(Vec3::new(0.0, 0.0, -1.0));
+        let rangefinder = ViewRangefinder3d::from_view_proj_matrix(&view_proj_matrix);
         assert_eq!(rangefinder.distance(&Mat4::IDENTITY), 1.0);
         assert_eq!(
             rangefinder.distance(&Mat4::from_translation(Vec3::new(0.0, 0.0, 1.0))),

crates/bevy_render/src/view/mod.rs

@@ -123,7 +123,12 @@ pub struct ExtractedView {
 impl ExtractedView {
     /// Creates a 3D rangefinder for a view
     pub fn rangefinder3d(&self) -> ViewRangefinder3d {
-        ViewRangefinder3d::from_view_matrix(&self.transform.compute_matrix())
+        if let Some(vp) = &self.view_projection {
+            ViewRangefinder3d::from_view_proj_matrix(vp)
+        } else {
+            let vp = self.projection * self.transform.compute_matrix().inverse();
+            ViewRangefinder3d::from_view_proj_matrix(&vp)
+        }
     }
 }