fudge depth offsets on Webgl

rerun-io · May 17, 2023 · fd6e25c · fd6e25c
1 parent 8a50ff2
commit fd6e25c
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Showing 2 changed files with 15 additions and 1 deletion.
diff --git a/crates/re_renderer/shader/utils/depth_offset.wgsl b/crates/re_renderer/shader/utils/depth_offset.wgsl
@@ -16,7 +16,8 @@ fn apply_depth_offset(position: Vec4, offset: f32) -> Vec4 {
 
         // 1.0 * eps _should_ be enough, but in practice it causes Z-fighting for unknown reasons.
         // Maybe because of GPU interpolation of vertex coordinates?
-        let eps = 5.0 * f32eps;
+        let BACKEND_SPECIFIC_DEPTH_FUDGE_FACTOR = 1.0; // Patched by shader processing on WebGL.
+        let eps = BACKEND_SPECIFIC_DEPTH_FUDGE_FACTOR * 5.0 * f32eps;
 
         return Vec4(
             position.xy,

diff --git a/crates/re_renderer/src/context.rs b/crates/re_renderer/src/context.rs
@@ -201,6 +201,19 @@ impl RenderContext {
                     "@invariant @builtin(position)".to_owned(),
                     "@builtin(position)".to_owned(),
                 ));
+        } else if adapter.get_info().backend == wgpu::Backend::Gl {
+            // On GLES/WebGL, the NDC clipspace range for depth is from -1 to 1.
+            // wgpu/Naga counteracts this by patching all vertex shader with:
+            // "gl_Position.yz = vec2(-gl_Position.y, gl_Position.z * 2.0 - gl_Position.w);",
+            // This is great, since it means that we can pretend depth is 0 to 1 as specified by WebGPU.
+            // But it considerably messes up depth precision.
+            gpu_resources
+                .shader_modules
+                .shader_text_workaround_replacements
+                .push((
+                    "let BACKEND_SPECIFIC_DEPTH_FUDGE_FACTOR = 1.0;".to_owned(),
+                    "let BACKEND_SPECIFIC_DEPTH_FUDGE_FACTOR = 100.0;".to_owned(),
+                ));
         }
 
         RenderContext {