From 9ed3cea3cae11f65d63a522d572b6e8edeee8a02 Mon Sep 17 00:00:00 2001
From: Albin Chaboissier <chalbin73@gmail.com>
Date: Wed, 9 Sep 2026 23:01:23 +0200
Subject: [PATCH] Z prepass

---
 shaders/voxel.wgsl | 16 ++++++++++++++--
 src/main.rs        | 26 +++++++++++++++-----------
 2 files changed, 29 insertions(+), 13 deletions(-)

diff --git a/shaders/voxel.wgsl b/shaders/voxel.wgsl
index e7b7ec4..9b3db90 100644
--- a/shaders/voxel.wgsl
+++ b/shaders/voxel.wgsl
@@ -6,7 +6,8 @@ struct VertexOutput
     @location(2) cam_pos: vec3<f32>,
     @location(3) world_pos: vec3<f32>,
     @location(4) @interpolate(flat) structure_id: u32,
-    @location(5) chunk_position: vec3<f32>
+    @location(5) chunk_position: vec3<f32>,
+    @location(6) ndc: vec4<f32>
 }
 
 struct ChunkImmediate
@@ -123,6 +124,7 @@ fn chunk(@builtin(vertex_index) index: u32, @location(0) position: vec3<f32>, @l
     output.world_pos = vertex + position;
     output.structure_id = id;
     output.chunk_position = position;
+    output.ndc = output_vertex;
 
     //let output = vec4<f32>(vertex, 1.0f);
     return output;
@@ -389,6 +391,14 @@ fn fragment_prepass(in: VertexOutput) -> FragmentPrepassOutput
 @fragment
 fn fragment(in: VertexOutput) -> FragmentOutput
 {
+    let surface_depth = in.ndc.z;
+    let prepass_depth = textureSample(prepass_depth, prepass_depth_sampler, in.ndc.xy).x;
+
+    if surface_depth <= prepass_depth
+    {
+        discard;
+    }
+
     //frag_out.color = vec4<f32>(2 * 0.01 / (100. + 0.01 - depth * (100. - 0.01)));
     let ray_dir = normalize(in.world_pos - in.cam_pos);
     let interp = box_inter(in.cam_pos - in.chunk_position, ray_dir, vec3(0.), vec3(1));
@@ -401,7 +411,9 @@ fn fragment(in: VertexOutput) -> FragmentOutput
     var frag_out: FragmentOutput;
     //frag_out.color = result.color;
     frag_out.color = result.color;
-    frag_out.depth = depth;
+    //frag_out.color = vec4<f32>(smpl);
+    //frag_out.color = vec4<f32>((2. * 0.01 * 100.) / (0.01 + 100. - prepass_depth * (100. - 0.01)));
+    //frag_out.depth = depth;
     return frag_out;
 
     //return vec4<f32>(ray_origin, 1.);
diff --git a/src/main.rs b/src/main.rs
index 859747b..6ee1c6f 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -429,23 +429,27 @@ impl State
                         @compute @workgroup_size(8, 8)
                         fn main(@builtin(global_invocation_id) id: vec3<u32>) 
                         {{
-                            let dp = vec2<i32>(id.xy);
-                            let sp = dp * {prepass_downsampling};
-
+                            let source_pos = vec2<i32>(id.xy);
                             var depth = 1.;
+                            depth = min(depth, textureLoad(input_tex, source_pos + vec2<i32>(0, 0)).x);
+                            depth = min(depth, textureLoad(input_tex, source_pos + vec2<i32>(1, 0)).x);
+                            depth = min(depth, textureLoad(input_tex, source_pos + vec2<i32>(0, 1)).x);
+                            depth = min(depth, textureLoad(input_tex, source_pos + vec2<i32>(1, 1)).x);
+
+                            let dest_pos = source_pos * {prepass_downsampling};
+
                             for(var ox = 0; ox < {prepass_downsampling}; ox ++)
                             {{
                                 for(var oy = 0; oy < {prepass_downsampling}; oy ++)
                                 {{
-                                    depth = min(depth, textureLoad(input_tex, sp + vec2<i32>(ox, oy)).x);
+                                     textureStore(
+                                         output_tex,
+                                         dest_pos + vec2<i32>(ox, oy),
+                                         vec4<f32>(depth)
+                                     );
                                 }}
                             }}
 
-                            textureStore(
-                                output_tex,
-                                dp,
-                                vec4<f32>(depth)
-                            );
                         }}
                     "
                     )
@@ -688,7 +692,7 @@ impl State
                 },
                 wgpu::BindGroupEntry {
                     binding: 1,
-                    resource: wgpu::BindingResource::TextureView(&self.upsampled_prepass_depth.1),
+                    resource: wgpu::BindingResource::TextureView(&self.prepass_depth.1),
                 },
             ],
         });
@@ -783,7 +787,7 @@ impl State
                     },
                 })],
                 depth_stencil_attachment: Some(wgpu::RenderPassDepthStencilAttachment {
-                    view: &self.depth_buffer.1,
+                    view: &self.prepass_depth_buffer.1,
                     depth_ops: Some(Operations {
                         load: wgpu::LoadOp::Clear(1.),
                         store: wgpu::StoreOp::Store,