From 7df1bab38a42d8a33bc50ca583d4be37bd9c9f0d Mon Sep 17 00:00:00 2001
From: Robert Swain <robert.swain@gmail.com>
Date: Tue, 13 Jul 2021 16:20:05 +0200
Subject: [PATCH] bevy_pbr2: Do manual shadow map depth comparisons for more
 flexibility

---
 pipelined/bevy_pbr2/src/render/light.rs |  4 +--
 pipelined/bevy_pbr2/src/render/mod.rs   |  4 +--
 pipelined/bevy_pbr2/src/render/pbr.wgsl | 33 +++++++++++++++----------
 3 files changed, 24 insertions(+), 17 deletions(-)

diff --git a/pipelined/bevy_pbr2/src/render/light.rs b/pipelined/bevy_pbr2/src/render/light.rs
index ccb7bdc11e357..3458265e23dba 100644
--- a/pipelined/bevy_pbr2/src/render/light.rs
+++ b/pipelined/bevy_pbr2/src/render/light.rs
@@ -200,7 +200,7 @@ impl FromWorld for ShadowShaders {
                 mag_filter: FilterMode::Nearest,
                 min_filter: FilterMode::Nearest,
                 mipmap_filter: FilterMode::Nearest,
-                compare: Some(CompareFunction::LessEqual),
+                compare: None,
                 ..Default::default()
             }),
             directional_light_sampler: render_device.create_sampler(&SamplerDescriptor {
@@ -210,7 +210,7 @@ impl FromWorld for ShadowShaders {
                 mag_filter: FilterMode::Nearest,
                 min_filter: FilterMode::Nearest,
                 mipmap_filter: FilterMode::Nearest,
-                compare: Some(CompareFunction::LessEqual),
+                compare: None,
                 ..Default::default()
             }),
         }
diff --git a/pipelined/bevy_pbr2/src/render/mod.rs b/pipelined/bevy_pbr2/src/render/mod.rs
index 0c03cc12d4ccf..e33d4ca878b2b 100644
--- a/pipelined/bevy_pbr2/src/render/mod.rs
+++ b/pipelined/bevy_pbr2/src/render/mod.rs
@@ -88,7 +88,7 @@ impl FromWorld for PbrShaders {
                     binding: 3,
                     visibility: ShaderStage::FRAGMENT,
                     ty: BindingType::Sampler {
-                        comparison: true,
+                        comparison: false,
                         filtering: false,
                     },
                     count: None,
@@ -109,7 +109,7 @@ impl FromWorld for PbrShaders {
                     binding: 5,
                     visibility: ShaderStage::FRAGMENT,
                     ty: BindingType::Sampler {
-                        comparison: true,
+                        comparison: false,
                         filtering: false,
                     },
                     count: None,
diff --git a/pipelined/bevy_pbr2/src/render/pbr.wgsl b/pipelined/bevy_pbr2/src/render/pbr.wgsl
index f99a149969b06..8b80ea725af04 100644
--- a/pipelined/bevy_pbr2/src/render/pbr.wgsl
+++ b/pipelined/bevy_pbr2/src/render/pbr.wgsl
@@ -131,11 +131,11 @@ var lights: Lights;
 [[group(0), binding(2)]]
 var point_shadow_textures: texture_depth_cube_array;
 [[group(0), binding(3)]]
-var point_shadow_textures_sampler: sampler_comparison;
+var point_shadow_textures_sampler: sampler;
 [[group(0), binding(4)]]
 var directional_shadow_textures: texture_depth_2d_array;
 [[group(0), binding(5)]]
-var directional_shadow_textures_sampler: sampler_comparison;
+var directional_shadow_textures_sampler: sampler;
 
 [[group(2), binding(0)]]
 var material: StandardMaterial;
@@ -398,13 +398,14 @@ fn fetch_point_shadow(light_id: i32, frag_position: vec4<f32>) -> f32 {
     let w = major_axis_magnitude;
     let depth = z / w;
 
-    // do the lookup, using HW PCF and comparison
-    // NOTE: Due to the non-uniform control flow above, we must use the Level variant of
-    //       textureSampleCompare to avoid undefined behaviour due to some of the fragments in
-    //       a quad (2x2 fragments) being processed not being sampled, and this messing with
-    //       mip-mapping functionality. The shadow maps have no mipmaps so Level just samples
-    //       from LOD 0.
-    return textureSampleCompareLevel(point_shadow_textures, point_shadow_textures_sampler, frag_ls, i32(light_id), depth);
+    let shadow_map_depth = textureSampleLevel(point_shadow_textures, point_shadow_textures_sampler, frag_ls, i32(light_id), 0.0);
+    var shadow: f32;
+    if (depth < shadow_map_depth) {
+        shadow = 1.0;
+    } else {
+        shadow = 0.0;
+    }
+    return shadow;
 }
 
 fn fetch_directional_shadow(light_id: i32, frag_position: vec4<f32>) -> f32 {
@@ -418,10 +419,16 @@ fn fetch_directional_shadow(light_id: i32, frag_position: vec4<f32>) -> f32 {
     let proj_correction = 1.0 / homogeneous_coords.w;
     // compute texture coordinates for shadow lookup
     let light_local = homogeneous_coords.xy * flip_correction * proj_correction + vec2<f32>(0.5, 0.5);
-    // do the lookup, using HW PCF and comparison
-    // NOTE: Due to non-uniform control flow above, we must use the level variant of the texture
-    //       sampler to avoid use of implicit derivatives causing possible undefined behavior.
-    return textureSampleCompareLevel(directional_shadow_textures, directional_shadow_textures_sampler, light_local, i32(light_id), homogeneous_coords.z * proj_correction);
+    let depth = homogeneous_coords.z * proj_correction;
+
+    let shadow_map_depth = textureSampleLevel(directional_shadow_textures, directional_shadow_textures_sampler, light_local, i32(light_id), 0.0);
+    var shadow: f32;
+    if (depth < shadow_map_depth) {
+        shadow = 1.0;
+    } else {
+        shadow = 0.0;
+    }
+    return shadow;
 }
 
 struct FragmentInput {