329 lines
8.0 KiB
Odin
329 lines
8.0 KiB
Odin
package bvh
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import "../collision"
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import "base:runtime"
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import "core:container/queue"
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import "core:log"
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import "core:math"
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import lg "core:math/linalg"
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import "core:mem"
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import rl "vendor:raylib"
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_ :: log
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_ :: rl
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_ :: lg
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Vec3 :: [3]f32
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AABB :: struct {
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min, max: Vec3,
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}
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// Helper struct to avoid passing verts/indices separately
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Mesh :: struct {
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vertices: []Vec3,
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indices: []u16,
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}
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BVH :: struct {
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nodes: []Node,
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// Triangle IDs. first_index = indices[primitive * 3]
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primitives: []u16,
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nodes_used: i32,
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}
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destroy_bvh :: proc(bvh: ^BVH) {
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delete(bvh.nodes)
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delete(bvh.primitives)
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}
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// Helper struct to store mesh data together with its bvh for convenience
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// You don't have to use it
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Mesh_BVH :: struct {
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bvh: BVH,
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mesh: Mesh,
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}
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Node :: struct {
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aabb: AABB,
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// Index of the left child, right child is left_child + 1
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child_or_prim_start: i32,
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prim_len: i32,
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}
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// uvw
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Bary :: [3]f32
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is_leaf_node :: #force_inline proc(node: Node) -> bool {
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return node.prim_len > 0
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}
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#assert(size_of(Node) == 32)
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build_bvh_from_mesh :: proc(mesh: Mesh, allocator := context.allocator) -> (mesh_bvh: Mesh_BVH) {
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vertices, indices := mesh.vertices, mesh.indices
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assert(len(indices) % 3 == 0)
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bvh := &mesh_bvh.bvh
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num_triangles := len(indices) / 3
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// Caller owned, allocator might be temp_allocator so do this before checkpoint below, otherwise we the result accidentally
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bvh.nodes, _ = mem.make_aligned([]Node, num_triangles * 2 - 1, size_of(Node), allocator)
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bvh.primitives = make([]u16, num_triangles, allocator)
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// Clean up after ourselves
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temp := runtime.default_temp_allocator_temp_begin()
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defer runtime.default_temp_allocator_temp_end(temp)
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// Temp stuff
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centroids := make([]Vec3, num_triangles, context.temp_allocator)
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aabbs := make([]AABB, num_triangles, context.temp_allocator)
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// Calculate centroids and aabbs
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for i in 0 ..< num_triangles {
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i1, i2, i3 := indices[i * 3], indices[i * 3 + 1], indices[i * 3 + 2]
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v1, v2, v3 := vertices[i1], vertices[i2], vertices[i3]
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centroids[i] = (v1 + v2 + v3) * 0.33333333333
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aabbs[i].min = Vec3{min(v1.x, v2.x, v3.x), min(v1.y, v2.y, v3.y), min(v1.z, v2.z, v3.z)}
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aabbs[i].max = Vec3{max(v1.x, v2.x, v3.x), max(v1.y, v2.y, v3.y), max(v1.z, v2.z, v3.z)}
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size := aabbs[i].max - aabbs[i].min
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assert(size.x >= 0)
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assert(size.y >= 0)
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assert(size.z >= 0)
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bvh.primitives[i] = u16(i)
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}
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bvh.nodes_used = 1 // root
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root := &bvh.nodes[0]
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root.child_or_prim_start = 0
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root.prim_len = i32(num_triangles)
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update_node_bounds(bvh, 0, aabbs)
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subdivide(bvh, 0, centroids, aabbs)
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return
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}
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/// Useful for a top level accel structure
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build_bvh_from_aabbs :: proc(aabbs: []AABB, allocator := context.allocator) -> (bvh: BVH) {
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bvh.nodes, _ = mem.make_aligned([]Node, len(aabbs) * 2 - 1, size_of(Node), allocator)
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bvh.primitives = make([]u16, len(aabbs), allocator)
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temp := runtime.default_temp_allocator_temp_begin()
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defer runtime.default_temp_allocator_temp_end(temp)
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// Temp stuff
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centroids := make([]Vec3, len(aabbs), context.temp_allocator)
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// Calculate centroids
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for i in 0 ..< len(aabbs) {
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centroids[i] = (aabbs[i].max + aabbs[i].min) * 0.5
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bvh.primitives[i] = u16(i)
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}
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bvh.nodes_used = 1
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root := &bvh.nodes[0]
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root.prim_len = i32(len(aabbs))
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update_node_bounds(&bvh, 0, aabbs)
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subdivide(&bvh, 0, centroids, aabbs)
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return
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}
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update_node_bounds :: proc(bvh: ^BVH, node_idx: i32, prim_aabbs: []AABB) {
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node := &bvh.nodes[node_idx]
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node.aabb.min = math.F32_MAX
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node.aabb.max = -math.F32_MAX
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for i in node.child_or_prim_start ..< node.child_or_prim_start + node.prim_len {
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prim_aabb := prim_aabbs[bvh.primitives[i]]
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node.aabb.min.x = min(node.aabb.min.x, prim_aabb.min.x)
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node.aabb.min.y = min(node.aabb.min.y, prim_aabb.min.y)
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node.aabb.min.z = min(node.aabb.min.z, prim_aabb.min.z)
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node.aabb.max.x = max(node.aabb.max.x, prim_aabb.max.x)
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node.aabb.max.y = max(node.aabb.max.y, prim_aabb.max.y)
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node.aabb.max.z = max(node.aabb.max.z, prim_aabb.max.z)
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}
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}
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subdivide :: proc(bvh: ^BVH, node_idx: i32, centroids: []Vec3, aabbs: []AABB) {
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node := &bvh.nodes[node_idx]
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if node.prim_len <= 2 {
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return
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}
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size := node.aabb.max - node.aabb.min
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// Split along longest axis
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largest_side := size.x
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split_axis := 0
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if size.y > largest_side {
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split_axis = 1
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largest_side = size.y
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}
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if size.z > largest_side {
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split_axis = 2
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}
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split_pos := node.aabb.min[split_axis] + size[split_axis] * 0.5
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// Partition
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i := node.child_or_prim_start
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j := i + node.prim_len - 1
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for i <= j {
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prim_i := bvh.primitives[i]
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prim_j := bvh.primitives[j]
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if centroids[prim_i][split_axis] < split_pos {
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i += 1
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} else {
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bvh.primitives[i] = prim_j
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bvh.primitives[j] = prim_i
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j -= 1
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}
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}
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left_count := i - node.child_or_prim_start
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if left_count == 0 || left_count == node.prim_len {
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return
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}
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left_child := bvh.nodes_used
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right_child := bvh.nodes_used + 1
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bvh.nodes_used += 2
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prim_start := node.child_or_prim_start
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node.child_or_prim_start = left_child
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bvh.nodes[left_child] = {}
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bvh.nodes[right_child] = {}
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bvh.nodes[left_child].child_or_prim_start = prim_start
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bvh.nodes[left_child].prim_len = left_count
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bvh.nodes[right_child].child_or_prim_start = i
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bvh.nodes[right_child].prim_len = node.prim_len - left_count
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node.prim_len = 0
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update_node_bounds(bvh, left_child, aabbs)
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update_node_bounds(bvh, right_child, aabbs)
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subdivide(bvh, left_child, centroids, aabbs)
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subdivide(bvh, right_child, centroids, aabbs)
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}
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Ray :: struct {
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origin, dir: Vec3,
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dir_inv: Vec3,
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}
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Collision :: struct {
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hit: bool,
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t: f32,
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// which primitive we hit
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prim: u16,
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// Barycentric coords of the hit triangle
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bary: Bary,
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// jStats
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aabb_tests: int,
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triangle_tests: int,
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}
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traverse_bvh_ray_mesh :: proc(bvh: ^BVH, mesh: Mesh, ray: Ray, out_collision: ^Collision) -> bool {
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ray := ray
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ray.dir_inv.x = 1.0 / ray.dir.x
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ray.dir_inv.y = 1.0 / ray.dir.y
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ray.dir_inv.z = 1.0 / ray.dir.z
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if !out_collision.hit {
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out_collision.t = math.F32_MAX
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}
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prev_t := out_collision.t
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internal_traverse_bvh_ray_triangles(bvh, mesh, ray, out_collision)
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return out_collision.hit && out_collision.t < prev_t
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}
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internal_traverse_bvh_ray_triangles :: proc(
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bvh: ^BVH,
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mesh: Mesh,
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ray: Ray,
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out_collision: ^Collision,
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) {
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temp := runtime.default_temp_allocator_temp_begin()
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defer runtime.default_temp_allocator_temp_end(temp)
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nodes_to_process: queue.Queue(i32)
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queue.init(&nodes_to_process, queue.DEFAULT_CAPACITY, context.temp_allocator)
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queue.push_back(&nodes_to_process, 0)
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for queue.len(nodes_to_process) > 0 {
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node_idx := queue.pop_front(&nodes_to_process)
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assert(node_idx < bvh.nodes_used)
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node := &bvh.nodes[node_idx]
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out_collision.aabb_tests += 1
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if !internal_ray_aabb_test(ray, node.aabb, out_collision.t) {
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continue
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}
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rl.DrawBoundingBox(
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{min = node.aabb.min, max = node.aabb.max},
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debug_int_to_color(node_idx),
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)
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if is_leaf_node(node^) {
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for i in node.child_or_prim_start ..< node.child_or_prim_start + node.prim_len {
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internal_ray_tri_test(ray, mesh, bvh.primitives[i], out_collision)
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}
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} else {
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left_node := node.child_or_prim_start
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queue.push_back_elems(&nodes_to_process, left_node, left_node + 1)
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}
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}
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}
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internal_ray_aabb_test :: proc(ray: Ray, box: AABB, min_t: f32) -> bool {
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ts, ok := collision.intersect_ray_aabb(ray.origin, ray.dir, collision.Aabb{box.min, box.max})
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return ok && ts[0] < min_t
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}
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// Möller–Trumbore intersection algorithm
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// https://jacco.ompf2.com/2022/04/13/how-to-build-a-bvh-part-1-basics/
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internal_ray_tri_test :: proc(ray: Ray, mesh: Mesh, tri: u16, col: ^Collision) {
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i1, i2, i3 := mesh.indices[tri * 3], mesh.indices[tri * 3 + 1], mesh.indices[tri * 3 + 2]
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v1, v2, v3 := mesh.vertices[i1], mesh.vertices[i2], mesh.vertices[i3]
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col.triangle_tests += 1
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rl.DrawTriangle3D(v1, v2, v3, debug_int_to_color(i32(tri) + 1))
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t, _, barycentric, ok := collision.intersect_segment_triangle(
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{ray.origin, ray.origin + ray.dir},
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{v1, v2, v3},
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)
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if ok && t < col.t {
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col.hit = true
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col.t = t
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col.prim = tri
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col.bary = barycentric
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}
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}
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