cvkg-render-gpu 0.3.2

//! Shadow pass types and KvasirNode — renders depth-only shadow map from
//! light's perspective using 3D mesh data.

use crate::kvasir::nodes::PassId;
use crate::kvasir::{ExecutionContext, KvasirNode, ResourceId};
use glam::Mat4;
use wgpu::Buffer;

/// Directional light for shadow rendering.
#[derive(Debug, Clone, Copy)]
pub struct DirectionalLight {
    pub direction: glam::Vec3,
    pub color: glam::Vec3,
    pub intensity: f32,
}

impl Default for DirectionalLight {
    fn default() -> Self {
        Self {
            direction: glam::Vec3::new(0.0, -1.0, 0.0),
            color: glam::Vec3::ONE,
            intensity: 1.0,
        }
    }
}

/// GPU resources for a single 3D mesh instance ready for rendering.
#[derive(Debug, Clone)]
pub struct GpuMesh3d {
    /// Vertex buffer (position, normal, UV, etc.).
    pub vertex_buffer: Buffer,
    /// Index buffer.
    pub index_buffer: Buffer,
    /// Number of indices to draw.
    pub index_count: u32,
    /// Per-instance model matrix.
    pub transform: Mat4,
    /// View depth for transparent sorting (world-space distance from camera).
    /// Used by TransparentNode for back-to-front rendering.
    pub view_depth: f32,
    /// Index of this instance in the 3D instance buffer.
    pub instance_index: u32,
}

/// Shadow pass node — renders depth-only shadow map from light's perspective.
pub struct ShadowNode {
    pub light: DirectionalLight,
    pub shadow_map: ResourceId,
    /// GPU-ready mesh instances to render into the shadow map.
    pub mesh_instances: Vec<GpuMesh3d>,
    /// Cascade splits for CSM.
    pub cascade_splits: [f32; 4],
    /// Camera's view projection matrix.
    pub camera_view_proj: Mat4,
}

impl KvasirNode for ShadowNode {
    fn label(&self) -> &'static str {
        "ShadowPass"
    }

    fn inputs(&self) -> &[ResourceId] {
        &[]
    }

    fn outputs(&self) -> &[ResourceId] {
        std::slice::from_ref(&self.shadow_map)
    }

    fn pass_id(&self) -> PassId {
        PassId::Shadow
    }

    fn execute(&self, ctx: &mut ExecutionContext) {
        let light_dir = self.light.direction.normalize();

        // 1. Compute 4 cascades VP matrices
        let inv_cam_vp = self.camera_view_proj.inverse();
        let ndc_ranges = [
            (0.0f32, 0.08f32),
            (0.08f32, 0.22f32),
            (0.22f32, 0.55f32),
            (0.55f32, 1.0f32),
        ];

        let mut cascade_vps = [glam::Mat4::IDENTITY; 4];
        for i in 0..4 {
            let (near_ndc, far_ndc) = ndc_ranges[i];
            let ndc_corners = [
                glam::Vec3::new(-1.0, -1.0, near_ndc),
                glam::Vec3::new(1.0, -1.0, near_ndc),
                glam::Vec3::new(-1.0, 1.0, near_ndc),
                glam::Vec3::new(1.0, 1.0, near_ndc),
                glam::Vec3::new(-1.0, -1.0, far_ndc),
                glam::Vec3::new(1.0, -1.0, far_ndc),
                glam::Vec3::new(-1.0, 1.0, far_ndc),
                glam::Vec3::new(1.0, 1.0, far_ndc),
            ];

            let mut world_corners = [glam::Vec3::ZERO; 8];
            let mut center = glam::Vec3::ZERO;
            for j in 0..8 {
                let p = inv_cam_vp.project_point3(ndc_corners[j]);
                world_corners[j] = p;
                center += p;
            }
            center /= 8.0;

            let mut radius = 0.0f32;
            for corner in &world_corners {
                radius = radius.max(corner.distance(center));
            }

            // Snap radius to prevent shimmering
            radius = (radius * 16.0).round() / 16.0;

            let light_pos = center - light_dir * radius * 2.0;
            let light_view = glam::Mat4::look_at_lh(light_pos, center, glam::Vec3::Y);
            let light_proj =
                glam::Mat4::orthographic_lh(-radius, radius, -radius, radius, 0.0, radius * 4.0);

            cascade_vps[i] = light_proj * light_view;
        }

        // 2. Update CSM buffer with the new cascade splits/VPs
        let csm = cvkg_core::render_tier::CsmUniforms {
            cascade_vps,
            cascade_splits: [
                self.cascade_splits[0],
                self.cascade_splits[1],
                self.cascade_splits[2],
                self.cascade_splits[3],
            ],
            _pad: [0.0; 4],
        };
        ctx.queue
            .write_buffer(&ctx.renderer.csm_buffer, 0, bytemuck::bytes_of(&csm));

        let shadow_texture = match &ctx.renderer.shadow_map_texture {
            Some(t) => t,
            None => {
                tracing::error!("ShadowNode: renderer missing shadow_map_texture");
                return;
            }
        };

        // 3. Render each cascade into its array layer
        for (i, vp) in cascade_vps.iter().enumerate() {
            // Write cascade_vps[i] into scene_buffer's light_vp field (offset 320)
            ctx.queue
                .write_buffer(&ctx.renderer.scene_buffer, 320, bytemuck::bytes_of(vp));

            let layer_view = shadow_texture.create_view(&wgpu::TextureViewDescriptor {
                label: Some(&format!("Surtr CSM Shadow Pass Layer {}", i)),
                dimension: Some(wgpu::TextureViewDimension::D2),
                base_array_layer: i as u32,
                array_layer_count: Some(1),
                ..wgpu::TextureViewDescriptor::default()
            });

            // Create a depth-only render pass.
            let mut pass = ctx.encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
                label: Some(&format!("Shadow Pass Cascade {}", i)),
                color_attachments: &[], // No color output.
                depth_stencil_attachment: Some(wgpu::RenderPassDepthStencilAttachment {
                    view: &layer_view,
                    depth_ops: Some(wgpu::Operations {
                        load: wgpu::LoadOp::Clear(1.0),
                        store: wgpu::StoreOp::Store,
                    }),
                    stencil_ops: None,
                }),
                timestamp_writes: None,
                occlusion_query_set: None,
                multiview_mask: None,
            });

            // Bind the shadow pipeline and scene uniforms.
            pass.set_pipeline(&ctx.renderer.shadow_pipeline);
            pass.set_bind_group(1, &ctx.renderer.berserker_bind_group, &[]);

            // For each mesh, set vertex/index buffers and draw depth only.
            for mesh in self.mesh_instances.iter() {
                pass.set_vertex_buffer(0, mesh.vertex_buffer.slice(..));
                pass.set_index_buffer(mesh.index_buffer.slice(..), wgpu::IndexFormat::Uint32);
                pass.draw_indexed(0..mesh.index_count, 0, 0..1);
            }
        }
    }
}