mod: implement explicit default-joint resolver

Author: VrUaCom

src/formats/mod/attachment.cpp

@@ -0,0 +1,31 @@
+#include "dmc_rengine/formats/mod/attachment.hpp"
+
+#include <cstddef>
+
+namespace dmc::rengine::formats::mod::attachment {
+
+DefaultJointResolution resolve_default_joint(
+    const Document& child,
+    const Document& host) noexcept {
+    DefaultJointResolution out;
+    out.selector = child.header.default_joint_index();
+
+    const auto host_world =
+        world_transform::build_model_space_world_matrices(host.transform_domain);
+    if (!host_world.has_value()) {
+        out.status = ResolveStatus::host_spatial_hierarchy_unavailable;
+        return out;
+    }
+
+    const auto selector = static_cast<std::size_t>(out.selector);
+    if (selector >= host_world->size()) {
+        out.status = ResolveStatus::selector_out_of_range;
+        return out;
+    }
+
+    out.host_joint_world = (*host_world)[selector];
+    out.status = ResolveStatus::resolved;
+    return out;
+}
+
+} // namespace dmc::rengine::formats::mod::attachment