FilamentGeometryBuffersBuilder.cpp

// ----------------------------------------------------------------------------
// -                        Open3D: www.open3d.org                            -
// ----------------------------------------------------------------------------
// Copyright (c) 2018-2024 www.open3d.org
// SPDX-License-Identifier: MIT
// ----------------------------------------------------------------------------

#include "open3d/visualization/rendering/filament/FilamentGeometryBuffersBuilder.h"

#include "open3d/geometry/BoundingVolume.h"
#include "open3d/geometry/LineSet.h"
#include "open3d/geometry/Octree.h"
#include "open3d/geometry/PointCloud.h"
#include "open3d/geometry/TriangleMesh.h"
#include "open3d/geometry/VoxelGrid.h"
#include "open3d/t/geometry/Geometry.h"
#include "open3d/t/geometry/LineSet.h"
#include "open3d/t/geometry/PointCloud.h"
#include "open3d/t/geometry/TriangleMesh.h"

namespace open3d {
namespace visualization {
namespace rendering {

namespace {
static const Eigen::Vector3d kDefaultVoxelColor(0.5, 0.5, 0.5);

// Coordinates of 8 vertices in a cuboid (assume origin (0,0,0), size 1)
const static std::vector<Eigen::Vector3i> kCuboidVertexOffsets{
        Eigen::Vector3i(0, 0, 0), Eigen::Vector3i(1, 0, 0),
        Eigen::Vector3i(0, 1, 0), Eigen::Vector3i(1, 1, 0),
        Eigen::Vector3i(0, 0, 1), Eigen::Vector3i(1, 0, 1),
        Eigen::Vector3i(0, 1, 1), Eigen::Vector3i(1, 1, 1),
};

// Vertex indices of 12 triangles in a cuboid, for right-handed manifold mesh
const static std::vector<Eigen::Vector3i> kCuboidTrianglesVertexIndices{
        Eigen::Vector3i(0, 2, 1), Eigen::Vector3i(0, 1, 4),
        Eigen::Vector3i(0, 4, 2), Eigen::Vector3i(5, 1, 7),
        Eigen::Vector3i(5, 7, 4), Eigen::Vector3i(5, 4, 1),
        Eigen::Vector3i(3, 7, 1), Eigen::Vector3i(3, 1, 2),
        Eigen::Vector3i(3, 2, 7), Eigen::Vector3i(6, 4, 7),
        Eigen::Vector3i(6, 7, 2), Eigen::Vector3i(6, 2, 4),
};

// Vertex indices of 12 lines in a cuboid
const static std::vector<Eigen::Vector2i> kCuboidLinesVertexIndices{
        Eigen::Vector2i(0, 1), Eigen::Vector2i(0, 2), Eigen::Vector2i(0, 4),
        Eigen::Vector2i(3, 1), Eigen::Vector2i(3, 2), Eigen::Vector2i(3, 7),
        Eigen::Vector2i(5, 1), Eigen::Vector2i(5, 4), Eigen::Vector2i(5, 7),
        Eigen::Vector2i(6, 2), Eigen::Vector2i(6, 4), Eigen::Vector2i(6, 7),
};

static void AddVoxelFaces(geometry::TriangleMesh& mesh,
                          const std::vector<Eigen::Vector3d>& vertices,
                          const Eigen::Vector3d& color) {
    for (const Eigen::Vector3i& triangle_vertex_indices :
         kCuboidTrianglesVertexIndices) {
        int n = int(mesh.vertices_.size());
        mesh.triangles_.push_back({n, n + 1, n + 2});
        mesh.vertices_.push_back(vertices[triangle_vertex_indices(0)]);
        mesh.vertices_.push_back(vertices[triangle_vertex_indices(1)]);
        mesh.vertices_.push_back(vertices[triangle_vertex_indices(2)]);
        mesh.vertex_colors_.push_back(color);
        mesh.vertex_colors_.push_back(color);
        mesh.vertex_colors_.push_back(color);
    }
}

static void AddLineFace(geometry::TriangleMesh& mesh,
                        const Eigen::Vector3d& start,
                        const Eigen::Vector3d& end,
                        const Eigen::Vector3d& half_width,
                        const Eigen::Vector3d& color) {
    int n = int(mesh.vertices_.size());
    mesh.triangles_.push_back({n, n + 1, n + 3});
    mesh.triangles_.push_back({n, n + 3, n + 2});
    mesh.vertices_.push_back(start - half_width);
    mesh.vertices_.push_back(start + half_width);
    mesh.vertices_.push_back(end - half_width);
    mesh.vertices_.push_back(end + half_width);
    mesh.vertex_colors_.push_back(color);
    mesh.vertex_colors_.push_back(color);
    mesh.vertex_colors_.push_back(color);
    mesh.vertex_colors_.push_back(color);
}

static std::shared_ptr<geometry::TriangleMesh> CreateTriangleMeshFromVoxelGrid(
        const geometry::VoxelGrid& voxel_grid) {
    auto mesh = std::make_shared<geometry::TriangleMesh>();
    auto num_voxels = voxel_grid.voxels_.size();
    mesh->vertices_.reserve(36 * num_voxels);
    mesh->vertex_colors_.reserve(36 * num_voxels);

    std::vector<Eigen::Vector3d>
            vertices;  // putting outside loop enables reuse
    for (auto& it : voxel_grid.voxels_) {
        vertices.clear();
        const geometry::Voxel& voxel = it.second;
        // 8 vertices in a voxel
        Eigen::Vector3d base_vertex =
                voxel_grid.origin_ +
                voxel.grid_index_.cast<double>() * voxel_grid.voxel_size_;
        for (const Eigen::Vector3i& vertex_offset : kCuboidVertexOffsets) {
            vertices.push_back(base_vertex + vertex_offset.cast<double>() *
                                                     voxel_grid.voxel_size_);
        }

        // Voxel color (applied to all points)
        Eigen::Vector3d voxel_color;
        if (voxel_grid.HasColors()) {
            voxel_color = voxel.color_;
        } else {
            voxel_color = kDefaultVoxelColor;
        }

        AddVoxelFaces(*mesh, vertices, voxel_color);
    }

    return mesh;
}

static std::shared_ptr<geometry::TriangleMesh> CreateTriangleMeshFromOctree(
        const geometry::Octree& octree) {
    auto mesh = std::make_shared<geometry::TriangleMesh>();

    // We cannot have a real line with a width in pixels, we can only fake a
    // line as rectangles. This value works nicely on the assumption that the
    // octree fills about 80% of the viewing area.
    double line_half_width = 0.0015 * octree.size_;

    auto f = [&mesh = *mesh, line_half_width](
                     const std::shared_ptr<geometry::OctreeNode>& node,
                     const std::shared_ptr<geometry::OctreeNodeInfo>& node_info)
            -> bool {
        Eigen::Vector3d base_vertex = node_info->origin_.cast<double>();
        std::vector<Eigen::Vector3d> vertices;
        for (const Eigen::Vector3i& vertex_offset : kCuboidVertexOffsets) {
            vertices.push_back(base_vertex + vertex_offset.cast<double>() *
                                                     double(node_info->size_));
        }

        auto leaf_node =
                std::dynamic_pointer_cast<geometry::OctreeColorLeafNode>(node);
        if (leaf_node) {
            AddVoxelFaces(mesh, vertices, leaf_node->color_);
        } else {
            // We cannot have lines in a TriangleMesh, obviously, so fake them
            // with two crossing planes.
            for (const Eigen::Vector2i& line_vertex_indices :
                 kCuboidLinesVertexIndices) {
                auto& start = vertices[line_vertex_indices(0)];
                auto& end = vertices[line_vertex_indices(1)];
                Eigen::Vector3d w(line_half_width, 0.0, 0.0);
                // if (end - start).dot({1, 0, 0}) ~= 0, then use z, not x
                if (std::abs(end.y() - start.y()) < 0.1 &&
                    std::abs(end.z() - start.z()) < 0.1) {
                    w = {0.0, 0.0, line_half_width};
                }
                AddLineFace(mesh, start, end, w, {0.0, 0.0, 0.0});

                w = {0.0, line_half_width, 0.0};
                // if (end - start).dot({0, 1, 0}) ~= 0, then use z, not y
                if (std::abs(end.x() - start.x()) < 0.1 &&
                    std::abs(end.z() - start.z()) < 0.1) {
                    w = {0.0, 0.0, line_half_width};
                }
                AddLineFace(mesh, start, end, w, {0.0, 0.0, 0.0});
            }
        }

        return false;
    };

    octree.Traverse(f);

    return mesh;
}

}  // namespace

class TemporaryLineSetBuilder : public LineSetBuffersBuilder {
public:
    explicit TemporaryLineSetBuilder(std::shared_ptr<geometry::LineSet> lines)
        : LineSetBuffersBuilder(*lines), lines_(lines) {}

private:
    std::shared_ptr<geometry::LineSet> lines_;
};

class TemporaryMeshBuilder : public TriangleMeshBuffersBuilder {
public:
    explicit TemporaryMeshBuilder(std::shared_ptr<geometry::TriangleMesh> mesh)
        : TriangleMeshBuffersBuilder(*mesh), mesh_(mesh) {}

private:
    std::shared_ptr<geometry::TriangleMesh> mesh_;
};

std::unique_ptr<GeometryBuffersBuilder> GeometryBuffersBuilder::GetBuilder(
        const geometry::Geometry3D& geometry) {
    using GT = geometry::Geometry::GeometryType;

    switch (geometry.GetGeometryType()) {
        case GT::TriangleMesh:
            return std::make_unique<TriangleMeshBuffersBuilder>(
                    static_cast<const geometry::TriangleMesh&>(geometry));

        case GT::PointCloud:
            return std::make_unique<PointCloudBuffersBuilder>(
                    static_cast<const geometry::PointCloud&>(geometry));

        case GT::LineSet:
            return std::make_unique<LineSetBuffersBuilder>(
                    static_cast<const geometry::LineSet&>(geometry));
        case GT::OrientedBoundingBox: {
            auto obb =
                    static_cast<const geometry::OrientedBoundingBox&>(geometry);
            auto lines = geometry::LineSet::CreateFromOrientedBoundingBox(obb);
            lines->PaintUniformColor(obb.color_);
            return std::make_unique<TemporaryLineSetBuilder>(lines);
        }
        case GT::AxisAlignedBoundingBox: {
            auto aabb = static_cast<const geometry::AxisAlignedBoundingBox&>(
                    geometry);
            auto lines =
                    geometry::LineSet::CreateFromAxisAlignedBoundingBox(aabb);
            lines->PaintUniformColor(aabb.color_);
            return std::make_unique<TemporaryLineSetBuilder>(lines);
        }
        case GT::VoxelGrid: {
            auto voxel_grid = static_cast<const geometry::VoxelGrid&>(geometry);
            auto mesh = CreateTriangleMeshFromVoxelGrid(voxel_grid);
            return std::make_unique<TemporaryMeshBuilder>(mesh);
        }
        case GT::Octree: {
            auto octree = static_cast<const geometry::Octree&>(geometry);
            auto mesh = CreateTriangleMeshFromOctree(octree);
            return std::make_unique<TemporaryMeshBuilder>(mesh);
        }
        default:
            break;
    }

    return nullptr;
}

std::unique_ptr<GeometryBuffersBuilder> GeometryBuffersBuilder::GetBuilder(
        const t::geometry::Geometry& geometry) {
    using GT = t::geometry::Geometry::GeometryType;

    switch (geometry.GetGeometryType()) {
        case GT::PointCloud: {
            const t::geometry::PointCloud& pointcloud = static_cast<const t::geometry::PointCloud&>(geometry);
            if (pointcloud.IsGaussianSplat()) {
                return std::make_unique<TGaussianSplatBuffersBuilder>(pointcloud);
            } else {
                return std::make_unique<TPointCloudBuffersBuilder>(pointcloud);
            }
        }
        case GT::TriangleMesh:
            return std::make_unique<TMeshBuffersBuilder>(
                    static_cast<const t::geometry::TriangleMesh&>(geometry));
        case GT::LineSet:
            return std::make_unique<TLineSetBuffersBuilder>(
                    static_cast<const t::geometry::LineSet&>(geometry));
        default:
            break;
    }

    return nullptr;
}

void GeometryBuffersBuilder::DeallocateBuffer(void* buffer,
                                              size_t size,
                                              void* user_ptr) {
    free(buffer);
}

}  // namespace rendering
}  // namespace visualization
}  // namespace open3d