From 5577a04a4093a529d2c64a24e1ab4c72941b5ff1 Mon Sep 17 00:00:00 2001
From: Valentin Popov <valentin@popov.link>
Date: Sat, 18 Jul 2026 17:20:37 +0400
Subject: feat(terrain): expose slot render dispatch

---
 crates/fparkan-terrain-format/src/lib.rs | 47 ++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

(limited to 'crates/fparkan-terrain-format/src/lib.rs')

diff --git a/crates/fparkan-terrain-format/src/lib.rs b/crates/fparkan-terrain-format/src/lib.rs
index 6e018c0..0051b82 100644
--- a/crates/fparkan-terrain-format/src/lib.rs
+++ b/crates/fparkan-terrain-format/src/lib.rs
@@ -183,6 +183,33 @@ pub struct TerrainSlotTable {
     pub slots_raw: Vec<[u8; SLOT_STRIDE]>,
 }
 
+/// The proven front fields of one 68-byte terrain slot record.
+///
+/// `Terrain.dll!CLandscape` supplies these fields to `GetShade`'s terrain
+/// batch dispatcher: `pair_table_index` selects the pointer-table entry and
+/// `pair_count` is the number of adjacent `u16` pairs to process. The pair
+/// payload and the later material/blend interpretation remain external to the
+/// disk record.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub struct TerrainSlotRenderDispatch {
+    /// Index into the runtime pair-pointer table.
+    pub pair_table_index: u16,
+    /// Number of adjacent `u16` pairs in that selected payload.
+    pub pair_count: u16,
+}
+
+impl TerrainSlotTable {
+    /// Returns the render-dispatch header for one decoded slot record.
+    #[must_use]
+    pub fn render_dispatch(&self, slot_index: usize) -> Option<TerrainSlotRenderDispatch> {
+        let raw = self.slots_raw.get(slot_index)?;
+        Some(TerrainSlotRenderDispatch {
+            pair_table_index: u16::from_le_bytes([raw[0], raw[1]]),
+            pair_count: u16::from_le_bytes([raw[2], raw[3]]),
+        })
+    }
+}
+
 /// Land mesh document.
 #[derive(Clone, Debug, PartialEq)]
 pub struct LandMeshDocument {
@@ -1460,6 +1487,26 @@ mod tests {
         );
     }
 
+    #[test]
+    fn slot_render_dispatch_retains_pair_table_index_and_count() {
+        let mut raw = [0_u8; SLOT_STRIDE];
+        raw[..2].copy_from_slice(&7_u16.to_le_bytes());
+        raw[2..4].copy_from_slice(&3_u16.to_le_bytes());
+        let slots = TerrainSlotTable {
+            header_raw: SLOT_HEADER_ZERO.to_vec(),
+            slots_raw: vec![raw],
+        };
+
+        assert_eq!(
+            slots.render_dispatch(0),
+            Some(TerrainSlotRenderDispatch {
+                pair_table_index: 7,
+                pair_count: 3,
+            })
+        );
+        assert_eq!(slots.render_dispatch(1), None);
+    }
+
     #[test]
     fn terrain_material_tag_decodes_two_sidecar_selectors() {
         let mut raw_face = face([0, 1, 2], [None, None, None]);
-- 
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