2 files changed, 185 insertions, 0 deletions
diff --git a/crates/render-core/src/lib.rs b/crates/render-core/src/lib.rs
new file mode 100644
index 0000000..8e0b5e8
--- /dev/null
+++ b/crates/render-core/src/lib.rs
@@ -0,0 +1,84 @@
+use msh_core::Model;
+
+#[derive(Clone, Debug)]
+pub struct RenderMesh {
+    pub vertices: Vec<[f32; 3]>,
+    pub batch_count: usize,
+}
+
+impl RenderMesh {
+    pub fn triangle_count(&self) -> usize {
+        self.vertices.len() / 3
+    }
+}
+
+/// Builds an expanded triangle list for a specific LOD/group pair.
+///
+/// The output is suitable for simple `glDrawArrays(GL_TRIANGLES, ...)` paths.
+pub fn build_render_mesh(model: &Model, lod: usize, group: usize) -> RenderMesh {
+    let mut vertices = Vec::new();
+    let mut batch_count = 0usize;
+
+    for node_index in 0..model.node_count {
+        let Some(slot_idx) = model.slot_index(node_index, lod, group) else {
+            continue;
+        };
+        let Some(slot) = model.slots.get(slot_idx) else {
+            continue;
+        };
+        let batch_start = usize::from(slot.batch_start);
+        let batch_end = batch_start.saturating_add(usize::from(slot.batch_count));
+        if batch_end > model.batches.len() {
+            continue;
+        }
+
+        for batch in &model.batches[batch_start..batch_end] {
+            let index_start = usize::try_from(batch.index_start).unwrap_or(usize::MAX);
+            let index_count = usize::from(batch.index_count);
+            let index_end = index_start.saturating_add(index_count);
+            if index_end > model.indices.len() || index_count < 3 {
+                continue;
+            }
+
+            for &idx in &model.indices[index_start..index_end] {
+                let final_idx_u64 = u64::from(batch.base_vertex).saturating_add(u64::from(idx));
+                let Ok(final_idx) = usize::try_from(final_idx_u64) else {
+                    continue;
+                };
+                let Some(pos) = model.positions.get(final_idx) else {
+                    continue;
+                };
+                vertices.push(*pos);
+            }
+            batch_count += 1;
+        }
+    }
+
+    RenderMesh {
+        vertices,
+        batch_count,
+    }
+}
+
+pub fn compute_bounds(vertices: &[[f32; 3]]) -> Option<([f32; 3], [f32; 3])> {
+    let mut iter = vertices.iter();
+    let first = iter.next()?;
+    let mut min_v = *first;
+    let mut max_v = *first;
+
+    for v in iter {
+        for i in 0..3 {
+            if v[i] < min_v[i] {
+                min_v[i] = v[i];
+            }
+            if v[i] > max_v[i] {
+                max_v[i] = v[i];
+            }
+        }
+    }
+
+    Some((min_v, max_v))
+}
+
+#[cfg(test)]
+mod tests;
diff --git a/crates/render-core/src/tests.rs b/crates/render-core/src/tests.rs
new file mode 100644
index 0000000..9c5eb5d
--- /dev/null
+++ b/crates/render-core/src/tests.rs
@@ -0,0 +1,101 @@
+use super::*;
+use msh_core::parse_model_payload;
+use nres::Archive;
+use std::fs;
+use std::path::{Path, PathBuf};
+
+fn collect_files_recursive(root: &Path, out: &mut Vec<PathBuf>) {
+    let Ok(entries) = fs::read_dir(root) else {
+        return;
+    };
+    for entry in entries.flatten() {
+        let path = entry.path();
+        if path.is_dir() {
+            collect_files_recursive(&path, out);
+        } else if path.is_file() {
+            out.push(path);
+        }
+    }
+}
+
+fn nres_test_files() -> Vec<PathBuf> {
+    let root = Path::new(env!("CARGO_MANIFEST_DIR"))
+        .join("..")
+        .join("..")
+        .join("testdata");
+    let mut files = Vec::new();
+    collect_files_recursive(&root, &mut files);
+    files.sort();
+    files
+        .into_iter()
+        .filter(|path| {
+            fs::read(path)
+                .map(|bytes| bytes.get(0..4) == Some(b"NRes"))
+                .unwrap_or(false)
+        })
+        .collect()
+}
+
+#[test]
+fn build_render_mesh_for_real_models() {
+    let archives = nres_test_files();
+    if archives.is_empty() {
+        eprintln!("skipping build_render_mesh_for_real_models: no NRes files in testdata");
+        return;
+    }
+
+    let mut models_checked = 0usize;
+    let mut meshes_non_empty = 0usize;
+    let mut bounds_non_empty = 0usize;
+
+    for archive_path in archives {
+        let archive = Archive::open_path(&archive_path)
+            .unwrap_or_else(|err| panic!("failed to open {}: {err}", archive_path.display()));
+        for entry in archive.entries() {
+            if !entry.meta.name.to_ascii_lowercase().ends_with(".msh") {
+                continue;
+            }
+            models_checked += 1;
+            let payload = archive.read(entry.id).unwrap_or_else(|err| {
+                panic!(
+                    "failed to read model '{}' from {}: {err}",
+                    entry.meta.name,
+                    archive_path.display()
+                )
+            });
+            let model = parse_model_payload(payload.as_slice()).unwrap_or_else(|err| {
+                panic!(
+                    "failed to parse model '{}' from {}: {err}",
+                    entry.meta.name,
+                    archive_path.display()
+                )
+            });
+            let mesh = build_render_mesh(&model, 0, 0);
+            if !mesh.vertices.is_empty() {
+                meshes_non_empty += 1;
+            }
+            if compute_bounds(&mesh.vertices).is_some() {
+                bounds_non_empty += 1;
+            }
+        }
+    }
+
+    assert!(models_checked > 0, "no MSH models found");
+    assert!(
+        meshes_non_empty > 0,
+        "all generated render meshes are empty"
+    );
+    assert_eq!(
+        meshes_non_empty, bounds_non_empty,
+        "bounds must be available for every non-empty mesh"
+    );
+}
+
+#[test]
+fn compute_bounds_handles_empty_and_non_empty() {
+    assert!(compute_bounds(&[]).is_none());
+    let bounds = compute_bounds(&[[1.0, 2.0, 3.0], [-2.0, 5.0, 0.5], [0.0, -1.0, 9.0]])
+        .expect("bounds expected");
+    assert_eq!(bounds.0, [-2.0, -1.0, 0.5]);
+    assert_eq!(bounds.1, [1.0, 5.0, 9.0]);
+}