fix(render): select terrain LOD from native camera cells

2 files changed, 329 insertions, 11 deletions

diff --git a/apps/fparkan-game/src/main.rs b/apps/fparkan-game/src/main.rs
index f3211af..f987bed 100644
--- a/apps/fparkan-game/src/main.rs
+++ b/apps/fparkan-game/src/main.rs
@@ -3,6 +3,7 @@
 //! `FParkan` render-planning composition root.
 
 mod camera_capture;
+mod terrain_lod;
 
 #[cfg(test)]
 use camera_capture::parse_legacy_camera_capture;
@@ -4626,6 +4627,7 @@ fn multiply_row_major(left: [f32; 16], right: [f32; 16]) -> [f32; 16] {
 
 struct StaticPreviewScene {
     mesh: VulkanStaticMesh,
+    terrain_lod: Option<terrain_lod::TerrainLodDraws>,
     native_handedness_by_range: HashMap<usize, i8>,
     type16_present_ranges: HashSet<usize>,
     materials: Vec<VulkanStaticMaterial>,
@@ -8019,6 +8021,11 @@ fn static_preview_mesh_and_materials(
         terrain,
         foundation,
     )?;
+    let (terrain_component, terrain_lod) = terrain_lod::prepare(
+        terrain_mesh,
+        terrain_component,
+        terrain_query.basement_foundation(),
+    )?;
     let terrain_materials = static_preview_terrain_base_materials(
         &mut terrain_material_loader,
         root,
@@ -8521,6 +8528,7 @@ fn static_preview_mesh_and_materials(
     let shadow_material_index = append_shadow_material(&mut materials)?;
     Ok(StaticPreviewScene {
         mesh,
+        terrain_lod,
         native_handedness_by_range,
         type16_present_ranges,
         materials,
@@ -9333,6 +9341,7 @@ fn run_static_vulkan_mode(
 
 struct StaticVulkanApp {
     mesh: VulkanStaticMesh,
+    terrain_lod: Option<terrain_lod::TerrainLodDraws>,
     native_handedness_by_range: HashMap<usize, i8>,
     type16_present_ranges: HashSet<usize>,
     materials: Vec<VulkanStaticMaterial>,
@@ -9439,6 +9448,7 @@ impl StaticVulkanApp {
             .collect();
         Self {
             mesh: preview.mesh,
+            terrain_lod: preview.terrain_lod,
             native_handedness_by_range: preview.native_handedness_by_range,
             type16_present_ranges: preview.type16_present_ranges,
             materials: preview.materials,
@@ -9509,6 +9519,12 @@ impl StaticVulkanApp {
         renderer: &mut VulkanSmokeRenderer,
         aspect: f32,
     ) -> Result<(), String> {
+        if let Some(lod) = &self.terrain_lod {
+            lod.report(
+                self.view_camera.position,
+                horizontal_fov(&self.view_camera, aspect),
+            )?;
+        }
         let approximate_portals = self
             .world_range_indices
             .iter()
@@ -9573,18 +9589,26 @@ impl StaticVulkanApp {
                 .map_err(|error| {
                     format!("configure world material category {range_index}: {error}")
                 })?;
-            renderer
-                .set_draw_range_index_count(
+            let count = world_draw_range_index_count(
+                &self.mesh,
+                range,
+                range.index_count,
+                effective_alpha,
+                self.view_camera.position,
+                self.native_handedness_by_range.get(&range_index).copied(),
+            );
+            let count = if let Some(lod) = &self.terrain_lod {
+                lod.index_count(
                     range_index,
-                    world_draw_range_index_count(
-                        &self.mesh,
-                        range,
-                        range.index_count,
-                        effective_alpha,
-                        self.view_camera.position,
-                        self.native_handedness_by_range.get(&range_index).copied(),
-                    ),
-                )
+                    count,
+                    self.view_camera.position,
+                    horizontal_fov(&self.view_camera, aspect),
+                )?
+            } else {
+                count
+            };
+            renderer
+                .set_draw_range_index_count(range_index, count)
                 .map_err(|error| {
                     format!("configure world draw range {range_index} count: {error}")
                 })?;
@@ -9642,6 +9666,7 @@ impl StaticVulkanApp {
         type16_present_ranges: &HashSet<usize>,
         world_range_index_counts: &HashMap<usize, u32>,
         native_handedness_by_range: &HashMap<usize, i8>,
+        terrain_lod: Option<&terrain_lod::TerrainLodDraws>,
         eye_world: [f32; 3],
         horizontal_fov: f32,
         active_materials: &HashMap<usize, ActiveMaterialState>,
@@ -9686,6 +9711,11 @@ impl StaticVulkanApp {
                 eye_world,
                 native_handedness_by_range.get(&range_index).copied(),
             );
+            let count = if let Some(lod) = terrain_lod {
+                lod.index_count(range_index, count, eye_world, horizontal_fov)?
+            } else {
+                count
+            };
             renderer
                 .set_draw_range_index_count(range_index, count)
                 .map_err(|error| format!("update world draw range {range_index} count: {error}"))?;
@@ -10295,6 +10325,7 @@ impl StaticVulkanApp {
             &self.type16_present_ranges,
             &self.world_range_index_counts,
             &self.native_handedness_by_range,
+            self.terrain_lod.as_ref(),
             frame.camera.position,
             horizontal_fov(&frame.camera, frame.aspect),
             &frame.material_update.active_materials,
@@ -13571,6 +13602,7 @@ mod tests {
         };
         let view_camera = free_camera.preview_frame(16.0 / 9.0);
         let preview = StaticPreviewScene {
+            terrain_lod: None,
             mesh: VulkanStaticMesh {
                 vertices: [[0.0, 0.0, 0.0], [1.0, 0.0, 0.0], [0.0, 1.0, 0.0]]
                     .into_iter()
diff --git a/apps/fparkan-game/src/terrain_lod.rs b/apps/fparkan-game/src/terrain_lod.rs
new file mode 100644
index 0000000..599178c
--- /dev/null
+++ b/apps/fparkan-game/src/terrain_lod.rs
@@ -0,0 +1,286 @@
+use fparkan_render_vulkan::{
+    project_land_msh_lod_to_static_mesh_in_world_space, VulkanStaticDrawRange, VulkanStaticMesh,
+};
+use fparkan_terrain::{BasementFoundation, TerrainLod, TerrainLodPlan};
+use fparkan_terrain_format::LandMeshDocument;
+
+pub(super) struct TerrainLodDraws {
+    plan: TerrainLodPlan,
+    ranges: Vec<(Option<usize>, TerrainLod)>,
+}
+
+impl TerrainLodDraws {
+    pub(super) fn index_count(
+        &self,
+        range: usize,
+        count: u32,
+        eye: [f32; 3],
+        fov: f32,
+    ) -> Result<u32, String> {
+        let Some(&(Some(node), lod)) = self.ranges.get(range) else {
+            return Ok(count);
+        };
+        let selected = self
+            .plan
+            .selected_lod(node, [eye[0], eye[1]], fov)
+            .ok_or_else(|| "invalid terrain LOD camera or cell".to_string())?;
+        Ok(if selected == lod { count } else { 0 })
+    }
+
+    pub(super) fn report(&self, eye: [f32; 3], fov: f32) -> Result<(), String> {
+        let mut counts = [0; 2];
+        for (range, &(_, lod)) in self.ranges.iter().enumerate() {
+            if self.index_count(range, 1, eye, fov)? != 0 {
+                counts[usize::from(lod == TerrainLod::Lod1)] += 1;
+            }
+        }
+        eprintln!(
+            "render_coverage terrain_lod_selected_ranges lod0={} lod1={}",
+            counts[0], counts[1]
+        );
+        Ok(())
+    }
+}
+
+pub(super) fn prepare(
+    terrain: &LandMeshDocument,
+    mut near_mesh: VulkanStaticMesh,
+    foundation: Option<&BasementFoundation>,
+) -> Result<(VulkanStaticMesh, Option<TerrainLodDraws>), String> {
+    let assignments = terrain.face_lod_assignments().map_err(|e| e.to_string())?;
+    if !assignments.iter().any(|a| a.lod == TerrainLod::Lod1) {
+        return Ok((near_mesh, None));
+    }
+    let plan = TerrainLodPlan::new(terrain, foundation)
+        .map_err(|e| format!("prepare terrain LOD: {e}"))?;
+    let near_nodes = if let Some(foundation) = foundation {
+        foundation
+            .fragments
+            .iter()
+            .map(|fragment| {
+                fragment
+                    .source_face
+                    .map(|face| {
+                        plan.source_face_node(face)
+                            .ok_or_else(|| "foundation LOD source face is missing".to_string())
+                    })
+                    .transpose()
+            })
+            .collect::<Result<Vec<_>, _>>()?
+    } else {
+        assignments
+            .iter()
+            .filter(|a| a.lod == TerrainLod::Lod0)
+            .map(|a| Some(a.node_index))
+            .collect()
+    };
+    let mut ranges = split_ranges(&mut near_mesh, &near_nodes, TerrainLod::Lod0)?;
+    if plan.has_far_geometry() {
+        let mut far_mesh =
+            project_land_msh_lod_to_static_mesh_in_world_space(terrain, TerrainLod::Lod1)
+                .map_err(|e| format!("project far terrain: {e}"))?;
+        let far_nodes = assignments
+            .iter()
+            .filter(|a| a.lod == TerrainLod::Lod1)
+            .map(|a| Some(a.node_index))
+            .collect::<Vec<_>>();
+        ranges.extend(split_ranges(&mut far_mesh, &far_nodes, TerrainLod::Lod1)?);
+        let vertex_offset = u32::try_from(near_mesh.vertices.len())
+            .map_err(|_| "terrain LOD vertex offset exceeds u32".to_string())?;
+        let index_offset = u32::try_from(near_mesh.indices.len())
+            .map_err(|_| "terrain LOD index offset exceeds u32".to_string())?;
+        for index in &mut far_mesh.indices {
+            *index = index
+                .checked_add(vertex_offset)
+                .ok_or_else(|| "far terrain vertex index overflows".to_string())?;
+        }
+        for range in &mut far_mesh.draw_ranges {
+            range.first_index = range
+                .first_index
+                .checked_add(index_offset)
+                .ok_or_else(|| "far terrain draw range overflows".to_string())?;
+        }
+        near_mesh.vertices.extend(far_mesh.vertices);
+        near_mesh.indices.extend(far_mesh.indices);
+        near_mesh.draw_ranges.extend(far_mesh.draw_ranges);
+    }
+    Ok((near_mesh, Some(TerrainLodDraws { plan, ranges })))
+}
+
+fn split_ranges(
+    mesh: &mut VulkanStaticMesh,
+    nodes: &[Option<usize>],
+    lod: TerrainLod,
+) -> Result<Vec<(Option<usize>, TerrainLod)>, String> {
+    if mesh.indices.len() / 3 != nodes.len() || !mesh.indices.len().is_multiple_of(3) {
+        return Err("terrain LOD triangle metadata does not match the index buffer".to_string());
+    }
+    let mut ranges = Vec::<VulkanStaticDrawRange>::new();
+    let mut bindings = Vec::new();
+    for &range in &mesh.draw_ranges {
+        if !range.first_index.is_multiple_of(3) || !range.index_count.is_multiple_of(3) {
+            return Err("terrain LOD range is not triangle aligned".to_string());
+        }
+        let first = range.first_index as usize / 3;
+        let end = first
+            .checked_add(range.index_count as usize / 3)
+            .filter(|&end| end <= nodes.len())
+            .ok_or_else(|| "terrain LOD range is outside triangle metadata".to_string())?;
+        let mut start = first;
+        while start < end {
+            let node = nodes[start];
+            let mut next = start + 1;
+            while next < end && nodes[next] == node {
+                next += 1;
+            }
+            let mut split = range;
+            split.first_index =
+                u32::try_from(start * 3).map_err(|_| "terrain LOD index overflows".to_string())?;
+            split.index_count = u32::try_from((next - start) * 3)
+                .map_err(|_| "terrain LOD count overflows".to_string())?;
+            ranges.push(split);
+            bindings.push((node, lod));
+            start = next;
+        }
+    }
+    mesh.draw_ranges = ranges;
+    Ok(bindings)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use fparkan_render_vulkan::VulkanStaticVertex;
+
+    #[test]
+    #[ignore = "requires licensed GOG Constructor resources"]
+    fn gog_constructor_lod0_cells_match_native_basement_mask() {
+        use fparkan_runtime::*;
+        use std::{num::NonZeroUsize, sync::Arc};
+        let root = std::env::var_os("FPARKAN_GAME_ROOT")
+            .map(std::path::PathBuf::from)
+            .unwrap_or_else(|| std::path::PathBuf::from(r"C:\GOG Games\Parkan - Iron Strategy"));
+        let mut engine = create(EngineServices::new(Arc::new(
+            fparkan_vfs::DirectoryVfs::new(root),
+        )))
+        .unwrap();
+        load_mission_static_preview_roots(
+            &mut engine,
+            MissionRequest {
+                key: r"MISSIONS\CAMPAIGN\CAMPAIGN.00\Mission.02\data.tma".to_string(),
+                mode: MissionMode::SingleMission,
+            },
+            NonZeroUsize::new(usize::MAX).unwrap(),
+        )
+        .unwrap();
+        let assets = loaded_mission_assets(&engine).unwrap();
+        let roots = loaded_mission_object_drafts(&engine).unwrap();
+        let terrain = loaded_terrain(&engine).unwrap().source_mesh().unwrap();
+        let footprints = super::super::mission_basement_footprints(assets, roots).unwrap();
+        let borrowed = footprints
+            .iter()
+            .map(|f| fparkan_terrain::BasementFootprint {
+                outer: &f.outer,
+                inner: &f.inner,
+                flatten_inner_to_mean_outer_z: f.flatten_inner_to_mean_outer_z,
+            })
+            .collect::<Vec<_>>();
+        let mut foundation =
+            fparkan_terrain::build_basement_foundations(terrain, &borrowed).unwrap();
+        let source =
+            fparkan_render_vulkan::project_land_msh_to_static_mesh_in_world_space(terrain).unwrap();
+        let (near, _) =
+            super::super::project_basement_foundation(terrain, &source, &mut foundation).unwrap();
+        let plan = TerrainLodPlan::new(terrain, Some(&foundation)).unwrap();
+        let forced = (0..terrain.nodes_raw.len() / 38)
+            .filter(|&node| plan.selected_lod(node, [-10_000.0; 2], 1.3) == Some(TerrainLod::Lod0))
+            .collect::<Vec<_>>();
+        // GOG Terrain.dll (hash in original-binaries.md), live Render +0x11A19:
+        // cells whose patch list at Render-this +0x7A30 has a nonzero count.
+        assert_eq!(
+            forced,
+            [
+                54, 55, 56, 57, 70, 71, 72, 73, 86, 87, 113, 114, 115, 129, 130, 131, 146, 147,
+                183, 184, 199, 200
+            ]
+        );
+        let (mesh, draws) = prepare(terrain, near, Some(&foundation)).unwrap();
+        let draws = draws.unwrap();
+        let mut checked = [false; 2];
+        for (range, &(node, lod)) in draws.ranges.iter().enumerate() {
+            if node != Some(40) {
+                continue;
+            }
+            let count = mesh.draw_ranges[range].index_count;
+            // Native cell 40 selects far at camera cell [2, 5], near at [2, 7].
+            assert_eq!(
+                draws
+                    .index_count(range, count, [300.42047, 556.282, 155.91914], 1.3)
+                    .unwrap(),
+                if lod == TerrainLod::Lod1 { count } else { 0 }
+            );
+            assert_eq!(
+                draws
+                    .index_count(range, count, [265.0, 795.0, 155.91914], 1.3)
+                    .unwrap(),
+                if lod == TerrainLod::Lod0 { count } else { 0 }
+            );
+            checked[usize::from(lod == TerrainLod::Lod1)] = true;
+        }
+        assert_eq!(checked, [true, true]);
+    }
+
+    #[test]
+    fn cell_ranges_keep_material_state_and_separate_generated_bands() {
+        let range = VulkanStaticDrawRange {
+            first_index: 0,
+            index_count: 12,
+            material_index: 7,
+            lightmap_index: u8::MAX,
+            batch_flags: 0,
+            terrain_base_only: true,
+            pipeline_state: super::super::world_pipeline_state(
+                fparkan_render::LegacyBlendMode::Opaque,
+                fparkan_render::LegacyDepthMode::TestWrite,
+            ),
+            alpha_test_reference: VulkanStaticDrawRange::NATIVE_DEFAULT_ALPHA_TEST_REFERENCE,
+        };
+        let mut mesh = VulkanStaticMesh {
+            vertices: [[0.0, 0.0, 0.0], [1.0, 0.0, 0.0], [0.0, 1.0, 0.0]]
+                .map(|position| VulkanStaticVertex {
+                    position,
+                    color: [1.0; 3],
+                    normal: [0.0, 0.0, 1.0],
+                    uv: [0.0; 2],
+                    detail_uv: [0.0; 2],
+                    overlay_alpha: 0.0,
+                })
+                .to_vec(),
+            indices: vec![0, 1, 2, 0, 1, 2, 0, 1, 2, 0, 1, 2],
+            draw_ranges: vec![range],
+        };
+        let nodes = [Some(4), Some(4), None, Some(5)];
+        let bindings = split_ranges(&mut mesh, &nodes, TerrainLod::Lod0).unwrap();
+        assert_eq!(
+            bindings,
+            vec![
+                (Some(4), TerrainLod::Lod0),
+                (None, TerrainLod::Lod0),
+                (Some(5), TerrainLod::Lod0)
+            ]
+        );
+        assert_eq!(
+            mesh.draw_ranges
+                .iter()
+                .map(|r| (r.first_index, r.index_count))
+                .collect::<Vec<_>>(),
+            vec![(0, 6), (6, 3), (9, 3)]
+        );
+        for split in &mesh.draw_ranges {
+            assert_eq!(split.material_index, 7);
+            assert_eq!(split.pipeline_state, range.pipeline_state);
+            assert!(split.terrain_base_only);
+        }
+        assert!(split_ranges(&mut mesh, &nodes[..3], TerrainLod::Lod0).is_err());
+    }
+}