/*
* Copyright 2019 Google LLC
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef SkReflected_DEFINED
#define SkReflected_DEFINED
#include "SkColor.h"
#include "SkRefCnt.h"
#include "SkTArray.h"
#include <string.h>
struct SkCurve;
class SkFieldVisitor;
struct SkPoint;
class SkString;
/**
* Classes and macros for a lightweight reflection system.
*
* Classes that derive from SkReflected have several features:
* - Access to an SkReflected::Type instance, via static GetType() or virtual getType()
* The Type instance can be used to create additional instances (fFactory), get the name
* of the type, and answer queries of the form "is X derived from Y".
* - Given a string containing a type name, SkReflected can create an instance of that type.
* - SkReflected::VisitTypes can be used to enumerate all Types.
*
* Together, this simplifies the implementation of serialization and other dynamic type factories.
*
* Finally, all SkReflected-derived types must implement visitFields, which provides field-level
* reflection, in conjunction with SkFieldVisitor. See SkFieldVisitor, below.
*
* To create a new reflected class:
* - Derive the class (directly or indirectly) from SkReflected.
* - Ensure that the class can be default constructed.
* - In the public area of the class declaration, add REFLECTED(<ClassName>, <BaseClassName>).
* If the class is abstract, use REFLECTED_ABSTRACT(<ClassName>, <BaseClassName>) instead.
* - Add a one-time call to REGISTER_REFLECTED(<ClassName>) at initialization time.
* - Implement visitFields(), as described below.
*/
class SkReflected : public SkRefCnt {
public:
typedef sk_sp<SkReflected>(*Factory)();
struct Type {
const char* fName;
const Type* fBase;
Factory fFactory;
bool fRegistered = false;
bool isDerivedFrom(const Type* t) const {
const Type* base = fBase;
while (base) {
if (base == t) {
return true;
}
base = base->fBase;
}
return false;
}
};
virtual const Type* getType() const = 0;
static const Type* GetType() {
static Type gType{ "SkReflected", nullptr, nullptr };
RegisterOnce(&gType);
return &gType;
}
bool isOfType(const Type* t) const {
const Type* thisType = this->getType();
return thisType == t || thisType->isDerivedFrom(t);
}
static sk_sp<SkReflected> CreateInstance(const char* name) {
for (const Type* type : gTypes) {
if (0 == strcmp(name, type->fName)) {
return type->fFactory();
}
}
return nullptr;
}
virtual void visitFields(SkFieldVisitor*) = 0;
static void VisitTypes(std::function<void(const Type*)> visitor);
protected:
static void RegisterOnce(Type* type) {
if (!type->fRegistered) {
gTypes.push_back(type);
type->fRegistered = true;
}
}
private:
static SkSTArray<16, const Type*, true> gTypes;
};
#define REFLECTED(TYPE, BASE) \
static sk_sp<SkReflected> CreateProc() { \
return sk_sp<SkReflected>(new TYPE()); \
} \
static const Type* GetType() { \
static Type gType{ #TYPE, BASE::GetType(), CreateProc }; \
RegisterOnce(&gType); \
return &gType; \
} \
const Type* getType() const override { return GetType(); }
#define REFLECTED_ABSTRACT(TYPE, BASE) \
static const Type* GetType() { \
static Type gType{ #TYPE, BASE::GetType(), nullptr }; \
RegisterOnce(&gType); \
return &gType; \
} \
const Type* getType() const override { return GetType(); }
#define REGISTER_REFLECTED(TYPE) TYPE::GetType()
///////////////////////////////////////////////////////////////////////////////
/**
* SkFieldVisitor is an interface that can be implemented by any class to visit all fields of
* SkReflected types, and of types that implement the visitFields() function.
*
* Classes implementing the interface must supply implementations of virtual functions that visit
* basic types (float, int, bool, SkString, etc...), as well as helper methods for entering the
* scope of an object or array.
*
* All visit functions supply a field name, and a non-constant reference to an actual field.
* This allows visitors to serialize or deserialize collections of objects, or perform edits on
* existing objects.
*
* Classes that implement visitFields (typically derived from SkReflected) should simply call
* visit() for each of their fields, passing a (unique) field name, and the actual field. If your
* class has derived fields, it's best to only visit() the fields that you would serialize, then
* enforce any constraints afterwards.
*
* See SkParticleSerialization.h for example visitors that perform serialization to and from JSON.
*/
class SkFieldVisitor {
public:
virtual ~SkFieldVisitor() {}
// Visit functions for primitive types, to be implemented by derived visitors.
virtual void visit(const char*, float&) = 0;
virtual void visit(const char*, int&) = 0;
virtual void visit(const char*, bool&) = 0;
virtual void visit(const char*, SkString&) = 0;
virtual void visit(const char*, SkPoint&) = 0;
virtual void visit(const char*, SkColor4f&) = 0;
// Accommodation for enums, where caller can supply a value <-> string map
struct EnumStringMapping {
int fValue;
const char* fName;
};
virtual void visit(const char*, int&, const EnumStringMapping*, int count) = 0;
// Specific virtual signature for SkCurve, to allow for heavily customized UI in SkGuiVisitor.
virtual void visit(const char* name, SkCurve& c);
// Default visit function for structs with no special behavior. It is assumed that any such
// struct implements visitFields(SkFieldVisitor*) to recursively visit each of its fields.
template <typename T>
void visit(const char* name, T& value) {
this->enterObject(name);
value.visitFields(this);
this->exitObject();
}
// Specialization for SkTArrays. In conjunction with the enterArray/exitArray virtuals, this
// allows visitors to resize an array (for deserialization), and apply a single edit operation
// (remove or move a single element). Each element of the array is visited as normal.
template <typename T, bool MEM_MOVE>
void visit(const char* name, SkTArray<T, MEM_MOVE>& arr) {
arr.resize_back(this->enterArray(name, arr.count()));
for (int i = 0; i < arr.count(); ++i) {
this->visit(nullptr, arr[i]);
}
this->exitArray().apply(arr);
}
// Specialization for sk_sp pointers to types derived from SkReflected. Those types are known
// to implement visitFields. This allows the visitor to modify the contents of the object, or
// even replace it with an entirely new object. The virtual function uses SkReflected as a
// common type, but uses SkReflected::Type to communicate the required base-class. In this way,
// the new object can be verified to match the type of the original (templated) pointer.
template <typename T>
void visit(const char* name, sk_sp<T>& obj) {
this->enterObject(name);
sk_sp<SkReflected> newObj = obj;
this->visit(newObj, T::GetType());
if (newObj != obj) {
if (!newObj || newObj->isOfType(T::GetType())) {
obj.reset(static_cast<T*>(newObj.release()));
} else {
obj.reset();
}
}
if (obj) {
obj->visitFields(this);
}
this->exitObject();
}
protected:
// Helper struct to allow exitArray to specify a single operation performed on the array.
struct ArrayEdit {
enum class Verb {
kNone,
kRemove,
kMoveForward,
};
Verb fVerb = Verb::kNone;
int fIndex = 0;
template <typename T, bool MEM_MOVE>
void apply(SkTArray<T, MEM_MOVE>& arr) const {
switch (fVerb) {
case Verb::kNone:
break;
case Verb::kRemove:
for (int i = fIndex; i < arr.count() - 1; ++i) {
arr[i] = arr[i + 1];
}
arr.pop_back();
break;
case Verb::kMoveForward:
if (fIndex > 0 && fIndex < arr.count()) {
std::swap(arr[fIndex - 1], arr[fIndex]);
}
break;
}
}
};
static const char* EnumToString(int value, const EnumStringMapping* map, int count) {
for (int i = 0; i < count; ++i) {
if (map[i].fValue == value) {
return map[i].fName;
}
}
return nullptr;
}
static int StringToEnum(const char* str, const EnumStringMapping* map, int count) {
for (int i = 0; i < count; ++i) {
if (0 == strcmp(str, map[i].fName)) {
return map[i].fValue;
}
}
return -1;
}
virtual void enterObject(const char* name) = 0;
virtual void exitObject() = 0;
virtual int enterArray(const char* name, int oldCount) = 0;
virtual ArrayEdit exitArray() = 0;
virtual void visit(sk_sp<SkReflected>&, const SkReflected::Type* baseType) = 0;
};
#endif // SkReflected_DEFINED