vk_expe/src/Planet.cpp

#include <Planet.h>
#include <Logger.h>

#include <cassert>
#include <vector>


Cell::Cell(
    const Vector3& corner00,
    const Vector3& corner01,
    const Vector3& corner10,
    const Vector3& corner11
)
    : m_corners{ corner00, corner01, corner10, corner11 }
    , m_height_factor(height_factor(m_corners))
    , m_cells{ nullptr, nullptr, nullptr, nullptr }
{}

Cell& Cell::cell(uint32_t cell_index) {
    assert(cell_index < CellCount);
    auto& cell = m_cells[cell_index];
    if(!cell)
    {
        // TODO
    }
    return *cell;
}

size_t Cell::vertex_count(uint32_t subdiv_count) {
    auto const s2 = 1 << subdiv_count;
    return s2 * s2 + 2 * s2 + 1;
}

size_t Cell::triangle_count(uint32_t subdiv_count) {
    auto const s2 = 1 << subdiv_count;
    return 2 * s2 * s2;
}

void Cell::build_mesh(
    Vector3AV positions, Vector3AV positions2, Vector3AV normals, TriangleAV triangles,
    uint32_t subdiv_count, Index index_offset
) const {
    auto const side_edge_count = (1u << subdiv_count);
    auto const side_vert_count = side_edge_count + 1;

    auto const quad_count = side_edge_count * side_edge_count;
    auto const tri_count = 2 * quad_count;
    auto const vert_count = side_vert_count * side_vert_count;

    assert(positions.size() == vert_count);
    assert(triangles.size() == tri_count);

    auto const index = [side_vert_count](uint32_t x, uint32_t y) -> uint32_t {
        return x + y * side_vert_count;
    };
    auto const vertex = [&normals, &index](uint32_t x, uint32_t y) -> Vector3& {
        return normals[index(x, y)];
    };

    vertex(              0,               0) = m_corners[0];
    vertex(side_edge_count,               0) = m_corners[1];
    vertex(              0, side_edge_count) = m_corners[2];
    vertex(side_edge_count, side_edge_count) = m_corners[3];

    struct QuadCell {
        uint32_t x0, x1, y0, y1;
    };
    std::vector<QuadCell> stack;
    stack.reserve(quad_count / 4);
    if(subdiv_count > 0) {
        stack.emplace_back(QuadCell {
            0, side_edge_count,
            0, side_edge_count,
        });
    }

    while(!stack.empty()) {
        const auto quad_cell = stack.back();
        stack.pop_back();

        auto const mx = (quad_cell.x0 + quad_cell.x1) / 2;
        auto const my = (quad_cell.y0 + quad_cell.y1) / 2;

        auto const& v00 = vertex(quad_cell.x0, quad_cell.y0);
        auto const& v01 = vertex(quad_cell.x1, quad_cell.y0);
        auto const& v10 = vertex(quad_cell.x0, quad_cell.y1);
        auto const& v11 = vertex(quad_cell.x1, quad_cell.y1);

        vertex(         mx, quad_cell.y0) =
            (v00 + v01).normalized();
        vertex(quad_cell.x0,          my) =
            (v00 + v10).normalized();
        vertex(mx, my) =
            (v00 + v01 + v10 + v11).normalized();
        vertex(quad_cell.x1,          my) =
            (v01 + v11).normalized();
        vertex(         mx, quad_cell.y1) =
            (v10 + v11).normalized();

        if(quad_cell.x0 + 1 < mx) {
            stack.emplace_back(QuadCell { mx, quad_cell.x1, my, quad_cell.y1 });
            stack.emplace_back(QuadCell { quad_cell.x0, mx, my, quad_cell.y1 });
            stack.emplace_back(QuadCell { mx, quad_cell.x1, quad_cell.y0, my });
            stack.emplace_back(QuadCell { quad_cell.x0, mx, quad_cell.y0, my });
        }
    }

    for (Index index = 0; index < normals.size(); index += 1) {
        positions[index] = normals[index];
    }

    int x_offset = (
        m_corners[0][0] < m_corners[1][0] ||
        m_corners[0][1] < m_corners[1][1] ||
        m_corners[0][2] < m_corners[1][2]
    )? -1: 1;
    int y_offset = (
        m_corners[0][0] < m_corners[2][0] ||
        m_corners[0][1] < m_corners[2][1] ||
        m_corners[0][2] < m_corners[2][2]
    )? -1: 1;
    for(Index y = 0; y < side_vert_count; y += 1) {
        for(Index x = 0; x < side_vert_count; x += 1) {
            Index x2 = x + (x & 0x01) * x_offset;
            Index y2 = y + (y & 0x01) * y_offset;

            positions2[index(x, y)] = positions[index(x2, y2)];
        }
    }

    auto triangleIndex = 0;
    bool flip = false; // (x_offset > 0) ^ (y_offset > 0);
    for(Index y = 0; y < side_edge_count; y += 1) {
        for(Index x = 0; x < side_edge_count; x += 1) {
            const auto i00 = index_offset + index(x, y);
            const auto i01 = i00 + 1;
            const auto i10 = i00 + side_vert_count;
            const auto i11 = i10 + 1;

            if (flip) {
                triangles[triangleIndex++] = Triangle { i00, i01, i11 };
                triangles[triangleIndex++] = Triangle { i00, i11, i10 };
            }
            else {
                triangles[triangleIndex++] = Triangle { i00, i01, i10 };
                triangles[triangleIndex++] = Triangle { i10, i01, i11 };
            }
        }
    }
}

Real Cell::height_factor(Vector3 corners[CornerCount]) {
    Vector3 c = (corners[0] + corners[1] + corners[2] + corners[3]).normalized();
    return Real(1) / corners[0].dot(c);
}



Planet::Planet()
    : m_cells {
        {
            Vector3(-1.0, -1.0, -1.0).normalized(),
            Vector3( 1.0, -1.0, -1.0).normalized(),
            Vector3(-1.0,  1.0, -1.0).normalized(),
            Vector3( 1.0,  1.0, -1.0).normalized(),
        },
        {
            Vector3( 1.0, -1.0, -1.0).normalized(),
            Vector3( 1.0, -1.0,  1.0).normalized(),
            Vector3( 1.0,  1.0, -1.0).normalized(),
            Vector3( 1.0,  1.0,  1.0).normalized(),
        },
        {
            Vector3( 1.0, -1.0,  1.0).normalized(),
            Vector3(-1.0, -1.0,  1.0).normalized(),
            Vector3( 1.0,  1.0,  1.0).normalized(),
            Vector3(-1.0,  1.0,  1.0).normalized(),
        },
        {
            Vector3(-1.0, -1.0,  1.0).normalized(),
            Vector3(-1.0, -1.0, -1.0).normalized(),
            Vector3(-1.0,  1.0,  1.0).normalized(),
            Vector3(-1.0,  1.0, -1.0).normalized(),
        },
        {
            Vector3(-1.0, -1.0,  1.0).normalized(),
            Vector3( 1.0, -1.0,  1.0).normalized(),
            Vector3(-1.0, -1.0, -1.0).normalized(),
            Vector3( 1.0, -1.0, -1.0).normalized(),
        },
        {
            Vector3(-1.0,  1.0, -1.0).normalized(),
            Vector3( 1.0,  1.0, -1.0).normalized(),
            Vector3(-1.0,  1.0,  1.0).normalized(),
            Vector3( 1.0,  1.0,  1.0).normalized(),
        },
    }
{}

void Planet::build_mesh(
    Vector3AV positions, Vector3AV positions2, Vector3AV normals, TriangleAV triangles,
    uint32_t subdiv_count, Index index_offset
) const {
    auto const vertex_count = Cell::vertex_count(subdiv_count);
    auto const index_count = Cell::triangle_count(subdiv_count);

    for(Index cell_index = 0; cell_index < CellCount; cell_index += 1) {
        auto sub_positions = positions.slice(
            cell_index * vertex_count, vertex_count
        );
        auto sub_positions2 = positions2.slice(
            cell_index * vertex_count, vertex_count
        );
        auto sub_normals = normals.slice(
            cell_index * vertex_count, vertex_count
        );
        auto sub_triangles = triangles.slice(
            cell_index * index_count, index_count
        );
        cell(cell_index).build_mesh(
            sub_positions,
            sub_positions2,
            sub_normals,
            sub_triangles,
            subdiv_count,
            index_offset + cell_index * vertex_count
        );
    }
}