fix(hatch): delay complex pattern LOD

Keep every pattern family visible until all projected spacings
become sub-pixel, then switch the hatch to solid.

Refs #569

tests/hatch_shader_lod.rs

@@ -0,0 +1,40 @@
+const STORAGE_SHADER: &str = include_str!("../src/shaders/hatch.wgsl");
+const TEXTURE_SHADER: &str = include_str!("../src/shaders/hatch_texture.wgsl");
+
+fn assert_all_family_lod(source: &str, name: &str) {
+    let module = naga::front::wgsl::parse_str(source)
+        .unwrap_or_else(|error| panic!("{name} WGSL must parse: {error}"));
+    naga::valid::Validator::new(
+        naga::valid::ValidationFlags::all(),
+        naga::valid::Capabilities::empty(),
+    )
+    .validate(&module)
+    .unwrap_or_else(|error| panic!("{name} WGSL must validate: {error}"));
+
+    assert!(
+        source.contains("var all_families_subpixel"),
+        "{name} must track the all-family LOD transition"
+    );
+    assert!(
+        source.contains("if all_families_subpixel"),
+        "{name} must solid-fill only at the all-family transition"
+    );
+    assert!(
+        !source.contains("if is_subpixel") && !source.contains("visible_families"),
+        "{name} must not skip individual families before LOD activates"
+    );
+    assert!(
+        !source.contains("min_spacing_world"),
+        "{name} must not solid-fill a complex pattern because of one dense family"
+    );
+}
+
+#[test]
+fn storage_hatch_lod_waits_for_every_family() {
+    assert_all_family_lod(STORAGE_SHADER, "storage hatch");
+}
+
+#[test]
+fn texture_hatch_lod_waits_for_every_family() {
+    assert_all_family_lod(TEXTURE_SHADER, "texture hatch");
+}