From b1db977176ea9eb2b78c1868274f20e827ff4f59 Mon Sep 17 00:00:00 2001
From: Marco Buono <thecoreh@gmail.com>
Date: Wed, 19 Apr 2023 02:08:50 -0300
Subject: [PATCH] Use depth prepass data to reject values that are in front of
 the current fragment

---
 crates/bevy_pbr/src/prepass/mod.rs           | 14 ++++++++------
 crates/bevy_pbr/src/render/pbr_lighting.wgsl |  9 +++++++--
 examples/3d/transmission.rs                  |  3 ++-
 3 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/crates/bevy_pbr/src/prepass/mod.rs b/crates/bevy_pbr/src/prepass/mod.rs
index 0659f20a32..958c253cc8 100644
--- a/crates/bevy_pbr/src/prepass/mod.rs
+++ b/crates/bevy_pbr/src/prepass/mod.rs
@@ -988,12 +988,14 @@ pub fn queue_prepass_material_meshes<M: Material>(
                 rangefinder.distance(&mesh_uniform.transform) + material.properties.depth_bias;
             match alpha_mode {
                 AlphaMode::Opaque => {
-                    opaque_phase.add(Opaque3dPrepass {
-                        entity: *visible_entity,
-                        draw_function: opaque_draw_prepass,
-                        pipeline_id,
-                        distance,
-                    });
+                    if !material.properties.is_transmissive {
+                        opaque_phase.add(Opaque3dPrepass {
+                            entity: *visible_entity,
+                            draw_function: opaque_draw_prepass,
+                            pipeline_id,
+                            distance,
+                        });
+                    }
                 }
                 AlphaMode::Mask(_) => {
                     alpha_mask_phase.add(AlphaMask3dPrepass {
diff --git a/crates/bevy_pbr/src/render/pbr_lighting.wgsl b/crates/bevy_pbr/src/render/pbr_lighting.wgsl
index d7ec5a3bdc..7af2fef4ec 100644
--- a/crates/bevy_pbr/src/render/pbr_lighting.wgsl
+++ b/crates/bevy_pbr/src/render/pbr_lighting.wgsl
@@ -336,13 +336,18 @@ fn fetch_transmissive_background(offset_position: vec2<f32>, frag_coord: vec3<f3
         // Magic numbers have been empirically chosen to produce blurry results that look “smooth”
         let dither = screen_space_dither(frag_coord.xy + vec2<f32>(f32(i) * 4773.0, f32(i) * 1472.0));
         let dither_offset = (blur_intensity * 7.0) * (blur_intensity * 7.0) * (30.0 * dither.yz + 0.03 * normalize(dither).xy) * vec2<f32>(1.0, -aspect);
+        let offset_position_with_dither = offset_position + dither_offset;
+
+        // Use depth prepass data to reject values that are in front of the current fragment
+        if (prepass_depth(vec4<f32>(offset_position_with_dither * view.viewport.zw, 0.0, 0.0), 0u) > frag_coord.z) {
+            continue;
+        }
 
         // Sample the view transmission texture at the offset position + dither offset, to get the background color
-        // TODO: Use depth prepass data to reject values that are in front of the current fragment
         result += textureSample(
             view_transmission_texture,
             view_transmission_sampler,
-            offset_position + dither_offset,
+            offset_position_with_dither,
         );
     }
 
diff --git a/examples/3d/transmission.rs b/examples/3d/transmission.rs
index 286d9be2d0..0ba8af8db4 100644
--- a/examples/3d/transmission.rs
+++ b/examples/3d/transmission.rs
@@ -17,7 +17,7 @@
 use std::f32::consts::PI;
 
 use bevy::{
-    core_pipeline::{bloom::BloomSettings, tonemapping::Tonemapping},
+    core_pipeline::{bloom::BloomSettings, prepass::DepthPrepass, tonemapping::Tonemapping},
     pbr::{NotShadowCaster, NotTransmittedShadowReceiver, PointLightShadowMap},
     prelude::*,
     render::view::ColorGrading,
@@ -343,6 +343,7 @@ fn setup(
             tonemapping: Tonemapping::TonyMcMapface,
             ..default()
         },
+        DepthPrepass,
         EnvironmentMapLight {
             diffuse_map: asset_server.load("environment_maps/pisa_diffuse_rgb9e5_zstd.ktx2"),
             specular_map: asset_server.load("environment_maps/pisa_specular_rgb9e5_zstd.ktx2"),