Merge pull request bevyengine#23 from rodolphito/meshlet-orthographic

Fix occlusion culling in orthographic views

Author: JMS55

crates/bevy_pbr/src/meshlet/cull_meshlets.wgsl

@@ -52,8 +52,9 @@ fn cull_meshlets(@builtin(global_invocation_id) thread_id: vec3<u32>) {
         let aabb = project_view_space_sphere_to_screen_space_aabb(bounding_sphere_center_view_space, bounding_sphere_radius);
 
         let depth_pyramid_size_mip_0 = vec2<f32>(textureDimensions(depth_pyramid, 0));
-        let width = (aabb.z - aabb.x) * depth_pyramid_size_mip_0.x;
-        let height = (aabb.w - aabb.y) * depth_pyramid_size_mip_0.y;
+        // we halve the size because the first depth mip resampling pass cut the full screen resolution into a power of two conservatively
+        let width = (aabb.z - aabb.x) * 0.5 * depth_pyramid_size_mip_0.x;
+        let height = (aabb.w - aabb.y) * 0.5 * depth_pyramid_size_mip_0.y;
         let depth_level = max(0, i32(ceil(log2(max(width, height))))); // TODO: Naga doesn't like this being a u32
         let depth_pyramid_size = vec2<f32>(textureDimensions(depth_pyramid, depth_level));
         let aabb_top_left = vec2<u32>(aabb.xy * depth_pyramid_size);
@@ -63,9 +64,15 @@ fn cull_meshlets(@builtin(global_invocation_id) thread_id: vec3<u32>) {
         let depth_quad_c = textureLoad(depth_pyramid, aabb_top_left + vec2(0u, 1u), depth_level).x;
         let depth_quad_d = textureLoad(depth_pyramid, aabb_top_left + vec2(1u, 1u), depth_level).x;
         let occluder_depth = min(min(depth_quad_a, depth_quad_b), min(depth_quad_c, depth_quad_d));
-
-        let sphere_depth = -view.projection[3][2] / (bounding_sphere_center_view_space.z + bounding_sphere_radius);
-        meshlet_visible &= sphere_depth >= occluder_depth;
+        if view.projection[3][3] == 1.0 {
+            // Orthographic
+            let sphere_depth =  view.projection[3][2] + (bounding_sphere_center_view_space.z + bounding_sphere_radius) * view.projection[2][2];
+            meshlet_visible &= sphere_depth >= occluder_depth;
+        } else {
+            // Perspective
+            let sphere_depth = -view.projection[3][2] / (bounding_sphere_center_view_space.z + bounding_sphere_radius);
+            meshlet_visible &= sphere_depth >= occluder_depth;
+        }
     }
 #endif
 
@@ -76,23 +83,31 @@ fn cull_meshlets(@builtin(global_invocation_id) thread_id: vec3<u32>) {
 
 // https://zeux.io/2023/01/12/approximate-projected-bounds
 fn project_view_space_sphere_to_screen_space_aabb(cp: vec3<f32>, r: f32) -> vec4<f32> {
-    let c = vec3(cp.xy, -cp.z);
-    // No need to clip near plane because frustum culling already checked that
+    let inv_width = view.projection[0][0] * 0.5;
+    let inv_height = view.projection[1][1] * 0.5;
+    if view.projection[3][3] == 1.0 {
+        // Orthographic
+        let min_x = cp.x - r;
+        let max_x = cp.x + r;
 
-    let cr = c * r;
-    let czr2 = c.z * c.z - r * r;
+        let min_y = cp.y - r;
+        let max_y = cp.y + r;
 
-    let vx = sqrt(c.x * c.x + czr2);
-    let min_x = (vx * c.x - cr.z) / (vx * c.z + cr.x);
-    let max_x = (vx * c.x + cr.z) / (vx * c.z - cr.x);
+        return vec4(min_x * inv_width, 1.0 - max_y * inv_height, max_x * inv_width, 1.0 - min_y * inv_height);
+    } else {
+        // Perspective
+        let c = vec3(cp.xy, -cp.z);
+        let cr = c * r;
+        let czr2 = c.z * c.z - r * r;
 
-    let vy = sqrt(c.y * c.y + czr2);
-    let min_y = (vy * c.y - cr.z) / (vy * c.z + cr.y);
-    let max_y = (vy * c.y + cr.z) / (vy * c.z - cr.y);
+        let vx = sqrt(c.x * c.x + czr2);
+        let min_x = (vx * c.x - cr.z) / (vx * c.z + cr.x);
+        let max_x = (vx * c.x + cr.z) / (vx * c.z - cr.x);
 
-    let p00 = view.projection[0][0];
-    let p11 = view.projection[1][1];
+        let vy = sqrt(c.y * c.y + czr2);
+        let min_y = (vy * c.y - cr.z) / (vy * c.z + cr.y);
+        let max_y = (vy * c.y + cr.z) / (vy * c.z - cr.y);
 
-    var aabb = vec4(min_x * p00, min_y * p11, max_x * p00, max_y * p11);
-    return aabb.xwzy * vec4(0.5, -0.5, 0.5, -0.5) + vec4(0.5);
+        return vec4(min_x * inv_width, -max_y * inv_height, max_x * inv_width, -min_y * inv_height) + vec4(0.5);
+    }
 }