Magnum::OpenDdl::Document class

Usage

To avoid needless allocations and string comparisons when using the parsed document, all structure and property names are represented as integer IDs. To parse a file, you first need to build a list of string names with their corresponding IDs for both structure and property names. The following example is a subset of the OpenGEX file format:

namespace OpenGex {

enum: Int {
    GeometryObject,
    IndexArray,
    Mesh,
    VertexArray
};

const std::initializer_list<OpenDdl::CharacterLiteral> structures{
    "GeometryObject",
    "IndexArray",
    "Mesh",
    "VertexArray"
}

enum: Int {
    attrib,
    key,
    motion_blur,
    primitive,
    shadow,
    two_sided,
    visible
};

const std::initializer_list<OpenDdl::CharacterLiteral> properties{
    "attrib",
    "key",
    "motion_blur",
    "primitive",
    "shadow",
    "two_sided",
    "visible"
};

}

Each enum value has corresponding string representation and the string identifiers are then passed to parse():

OpenDdl::Document d;
bool parsed = d.parse(data, OpenGex::structures, OpenGex::properties);

If the file contains structures or properties which are not included in the identifer lists, these are parsed with UnknownIdentifier ID. If the document has syntax errors, the function returns false and prints detailed diagnostics on Corrade::Utility::Error output. After parsing you can traverse the document using IDs from the enums:

for(OpenDdl::Structure geometryObject: d.childrenOf(OpenGex::GeometryObject)) {
    // Decide about primitive
    if(Containers::Optional<OpenDdl::Property> primitive = geometryObject.findPropertyOf(OpenGex::primitive)) {
        if(!primitive->isTypeCompatibleWith(OpenDdl::Type::String)) {
            // error ...
        }

        std::string str = primitive->as<std::string>();
        if(str == "triangles") {
            // ...
        } else if(str == "lines") {
            // ...
        } // ...
    } else {
        // ...
    }

    // Parse vertex array
    if(Containers::Optional<OpenDdl::Structure> vertexArray = geometryObject.findFirstChildOf(OpenGex::VertexArray)) {
        if(!vertexArray->hasChildren() || vertexArray->firstChild().type() != OpenDdl::Type::Float) {
            // error ...
        }

        Containers::ArrayView<const Float> vertexArray = vertexArray->firstChild().asArray<Float>();
        // ...

    } else {
        // error ...
    }
}

As you can see, the error checking can get pretty tiresome after a while. That's when document validation proves to be useful. The validation is just rough and checks only proper document hierarchy, allowed structure and property types, structure count and presence of required properties, but that's often enough to avoid most of the redundant checks. You define which structures can appear at document level and then for each structure what properties and which substructures it can have. Again a (very stripped down) subset of OpenGEX specification:

namespace OpenGex {

using namespace OpenDdl::Validation;

// GeometryObject and Metric can be root structures
const Structures rootStructures{
    {GeometryObject, {}},
    {Metric, {}}
};

// Info about particular structures
const std::initializer_list<Structure> structureInfo{
    // Metric structure has required key string property and contains exactly
    // one float or string primitive substructure with exactly one value
    {Metric,            Properties{{key, PropertyType::String, RequiredProperty}},
                        Primitives{Type::Float,
                                   Type::String}, 1, 1},

    // GeometryObject structure has optional visible and shadow boolean
    // properties and one or more Mesh substructures
    {GeometryObject,    Properties{{visible, OpenDdl::PropertyType::Bool, OptionalProperty},
                                   {shadow, OpenDdl::PropertyType::Bool, OptionalProperty}},
                        Structures{{Mesh, {1, 0}}}},

    // Mesh structure has optional lod and primitive properties, at least one
    // VertexArray substructure and zero or more IndexArray substructures
    {Mesh,              Properties{{lod, OpenDdl::PropertyType::UnsignedInt, OptionalProperty},
                                   {primitive, OpenDdl::PropertyType::String, OptionalProperty}},
                        Structures{{VertexArray, {1, 0}},
                                   {IndexArray, {}}}},

    // IndexArray structure has exactly one unsigned primitive substructure
    // with any number of values
    {IndexArray,        Primitives{OpenDdl::Type::UnsignedByte,
                                   OpenDdl::Type::UnsignedShort,
                                   OpenDdl::Type::UnsignedInt}, 1, 0},

    // VertexArray structure has required attrib property and exactly one float
    // substructure with any number of values
    {VertexArray,       Properties{{attrib, OpenDdl::PropertyType::String, RequiredProperty}},
                        Primitives{OpenDdl::Type::Float}, 1, 0}
};

}

You then pass it to validate() and check the return value. As with parse(), structures with UnknownIdentifier ID are ignored and if the validation fails, detailed diagnostics is printed on Corrade::Utility::Error output:

bool valid = d.validate(OpenGex::rootStructures, OpenGex::structureInfo);

If the document is valid, you can access child structures and properties directly with e.g. Structure::firstChildOf(), Structure::propertyOf() etc. instead of using Structure::findFirstChildOf(), Structure::findPropertyOf() etc. and checking return value all the time:

// Decide about primitive
if(Containers::Optional<OpenDdl::Property> primitive = geometryObject.findPropertyOf(OpenGex::primitive)) {
    auto&& str = primitive->as<std::string>();
    if(str == "triangles") {
        // ...
    } else if(str == "lines") {
        // ...
    } // ...
} else {
    // ...
}

// Parse vertex array
OpenDdl::Structure vertexArray = geometryObject.firstChildOf(OpenGex::VertexArray);
auto&& attrib = vertexArray.propertyOf(OpenGex::attrib).as<std::string>();
if(attrib == "position") {
    // ...
} else if(attrib == "normal") {
    // ...
}

// Parse vertex array data
Containers::ArrayView<const Float> data = vertexArray.firstChild().asArray<Float>();
// ...

Constructors, destructors, conversion operators

Document() explicit

Constructor.

Document(const Document&) deleted

Copying is disabled.

Document(Document&&) deleted

Moving is disabled.

Public functions

auto operator=(const Document&) -> Document& deleted

Copying is disabled.

auto operator=(Document&&) -> Document& deleted

Moving is disabled.

auto parse(Containers::ArrayView<const char> data, std::initializer_list<CharacterLiteral> structureIdentifiers, std::initializer_list<CharacterLiteral> propertyIdentifiers) -> bool

Parse data.

auto isEmpty() -> bool

Whether the document is empty.

auto findFirstChild() const -> Containers::Optional<Structure>

Find first top-level structure in the document.

auto firstChild() const -> Structure

First top-level structure in the document.

auto children() const -> Implementation::StructureList

Top-level structures.

auto findFirstChildOf(Type type) const -> Containers::Optional<Structure>

Find first custom top-level structure of given type.

auto findFirstChildOf(Int identifier) const -> Containers::Optional<Structure>

Find first custom top-level structure of given identifier.

auto findFirstChildOf(std::initializer_list<Int> identifiers) const -> Containers::Optional<Structure>

auto findFirstChildOf(Containers::ArrayView<const Int> identifiers) const -> Containers::Optional<Structure>

auto firstChildOf(Type type) const -> Structure

First custom top-level structure of given type.

auto firstChildOf(Int identifier) const -> Structure

First custom top-level structure of given identifier.

template<class ... T>

auto childrenOf(Int identifier, T... identifiers) const -> Implementation::StructureOfList<sizeof...(T)+1>

Top-level structures of given identifier.

auto validate(Validation::Structures allowedRootStructures, std::initializer_list<Validation::Structure> structures) const -> bool

Validate document.

Function documentation

for(Structure s: document.children()) {
    // ...
}

for(Structure s: document.childrenOf(...)) {
    // ...
}