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Add a callback to select which element are written #173

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merged 4 commits into from
Dec 28, 2023
Merged

Add a callback to select which element are written #173

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91ce3ec
Use a callback to select which elements should be written
robUx4 Dec 18, 2023
213380d
remove ForceNoDefault()
robUx4 Dec 18, 2023
0391375
use std::function as callback for ShouldWrite
mbunkus Dec 27, 2023
8b6c24e
avoid "unused variable" warnings
mbunkus Dec 27, 2023
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4 changes: 2 additions & 2 deletions ebml/EbmlBinary.h
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Expand Up @@ -32,9 +32,9 @@ class EBML_DLL_API EbmlBinary : public EbmlElement {

bool ValidateSize() const override {return GetSize() < 0x7FFFFFFF;} // we don't mind about what's inside

filepos_t RenderData(IOCallback & output, bool bForceRender, bool bWithDefault = false) override;
filepos_t RenderData(IOCallback & output, bool bForceRender, ShouldWrite writeFilter = WriteSkipDefault) override;
filepos_t ReadData(IOCallback & input, ScopeMode ReadFully = SCOPE_ALL_DATA) override;
filepos_t UpdateSize(bool bWithDefault = false, bool bForceRender = false) override;
filepos_t UpdateSize(ShouldWrite writeFilter = WriteSkipDefault, bool bForceRender = false) override;

void SetBuffer(const binary *Buffer, const std::uint32_t BufferSize) {
Data = const_cast<binary *>(Buffer);
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4 changes: 2 additions & 2 deletions ebml/EbmlCrc32.h
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Expand Up @@ -20,9 +20,9 @@ namespace libebml {
DECLARE_EBML_BINARY(EbmlCrc32)
public:
bool ValidateSize() const override {return GetSize() == 4;}
filepos_t RenderData(IOCallback & output, bool bForceRender, bool bWithDefault = false) override;
filepos_t RenderData(IOCallback & output, bool bForceRender, ShouldWrite writeFilter = WriteSkipDefault) override;
filepos_t ReadData(IOCallback & input, ScopeMode ReadFully = SCOPE_ALL_DATA) override;
// filepos_t UpdateSize(bool bWithDefault = false);
// filepos_t UpdateSize(ShouldWrite writeFilter = WriteSkipDefault);

bool IsDefaultValue() const override {
return false;
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4 changes: 2 additions & 2 deletions ebml/EbmlDate.h
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Expand Up @@ -40,7 +40,7 @@ class EBML_DLL_API EbmlDate : public EbmlElement {
/*!
\note no Default date handled
*/
filepos_t UpdateSize(bool /* bWithDefault = false */, bool /* bForceRender = false */) override {
filepos_t UpdateSize(ShouldWrite /* writeFilter */, bool /* bForceRender = false */) override {
if(!ValueIsSet())
SetSize_(0);
else
Expand All @@ -57,7 +57,7 @@ class EBML_DLL_API EbmlDate : public EbmlElement {
}

private:
filepos_t RenderData(IOCallback & output, bool bForceRender, bool bWithDefault = false) override;
filepos_t RenderData(IOCallback & output, bool bForceRender, ShouldWrite writeFilter = WriteSkipDefault) override;

std::int64_t myDate{0}; ///< internal format of the date

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31 changes: 24 additions & 7 deletions ebml/EbmlElement.h
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Expand Up @@ -13,6 +13,7 @@
#include "IOCallback.h"

#include <cassert>
#include <functional>

namespace libebml {

Expand Down Expand Up @@ -293,6 +294,21 @@ class EBML_DLL_API EbmlSemanticContext {
*/
class EBML_DLL_API EbmlElement {
public:
// callback to tell if the element should be written or not
// \return true if the element should be written
using ShouldWrite = std::function<bool(const EbmlElement &)>;

// write only elements that don't have their default value set
static bool WriteSkipDefault(const EbmlElement &elt) {
if (elt.IsDefaultValue())
return false;
return true;
}

static bool WriteAll(const EbmlElement &) {
return true;
}

explicit EbmlElement(const EbmlCallbacks &, std::uint64_t aDefaultSize, bool bValueSet = false);
virtual ~EbmlElement() = default;
EbmlElement& operator=(const EbmlElement&) = delete;
Expand Down Expand Up @@ -345,11 +361,11 @@ class EBML_DLL_API EbmlElement {
return ElementPosition;
}

std::uint64_t ElementSize(bool bWithDefault = false) const; /// return the size of the header+data, before writing
std::uint64_t ElementSize(ShouldWrite writeFilter = WriteSkipDefault) const; /// return the size of the header+data, before writing

filepos_t Render(IOCallback & output, bool bWithDefault = false, bool bKeepPosition = false, bool bForceRender = false);
filepos_t Render(IOCallback & output, ShouldWrite writeFilter = WriteSkipDefault, bool bKeepPosition = false, bool bForceRender = false);

virtual filepos_t UpdateSize(bool bWithDefault = false, bool bForceRender = false) = 0; /// update the Size of the Data stored
virtual filepos_t UpdateSize(ShouldWrite writeFilter = WriteSkipDefault, bool bForceRender = false) = 0; /// update the Size of the Data stored
virtual filepos_t GetSize() const {return Size;} /// return the size of the data stored in the element, on reading

virtual filepos_t ReadData(IOCallback & input, ScopeMode ReadFully = SCOPE_ALL_DATA) = 0;
Expand Down Expand Up @@ -380,10 +396,9 @@ class EBML_DLL_API EbmlElement {
/*!
\brief void the content of the element (replace by EbmlVoid)
*/
std::uint64_t VoidMe(IOCallback & output, bool bWithDefault = false) const;
std::uint64_t VoidMe(IOCallback & output, ShouldWrite writeFilter = WriteSkipDefault) const;

bool DefaultISset() const {return DefaultIsSet;}
void ForceNoDefault() {SetDefaultIsSet(false);}
virtual bool IsDefaultValue() const = 0;
bool IsFiniteSize() const {return bSizeIsFinite;}

Expand All @@ -406,13 +421,13 @@ class EBML_DLL_API EbmlElement {
*/
static EbmlElement *CreateElementUsingContext(const EbmlId & aID, const EbmlSemanticContext & Context, int & LowLevel, bool IsGlobalContext, bool bAllowDummy = false, unsigned int MaxLowerLevel = 1);

filepos_t RenderHead(IOCallback & output, bool bForceRender, bool bWithDefault = false, bool bKeepPosition = false);
filepos_t RenderHead(IOCallback & output, bool bForceRender, ShouldWrite writeFilter = WriteSkipDefault, bool bKeepPosition = false);
filepos_t MakeRenderHead(IOCallback & output, bool bKeepPosition);

/*!
\brief prepare the data before writing them (in case it's not already done by default)
*/
virtual filepos_t RenderData(IOCallback & output, bool bForceRender, bool bWithDefault = false) = 0;
virtual filepos_t RenderData(IOCallback & output, bool bForceRender, ShouldWrite writeFilter = WriteSkipDefault) = 0;

/*!
\brief special constructor for cloning
Expand Down Expand Up @@ -441,4 +456,6 @@ class EBML_DLL_API EbmlElement {

} // namespace libebml

#define EBML_WRITE_FILTER 1
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I… don't like this #define. Consumers can already use the version number #defines in order to differentiate between v1 & v2 of the library.

Not sure how I'll handle it in MKVToolNix. Will have to look into how many places will have to be changed as I'm generally not a fan of a lot of conditional compilation anyway. Maybe I'll just throw the switch & require v2 as soon as I add support for it.

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The define is there to tell v2 users which API they can expect. Once v2 is stable we can remove it and everyone should assume it's there for v2 code. In other words it's to make your life easier if you want to support the old and new API in your codebase for a while. I don't mind removing it and you handle it on your side.

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Makes sense, but isn't needed, at least not for me. As there's no official release of v2 yet, I won't support different snapshots of the upcoming v2 API in MKVToolNix. I'll try my best to support v1 & the latest v2 simultaneously, but even that is in question with this RFC.


#endif // LIBEBML_ELEMENT_H
4 changes: 2 additions & 2 deletions ebml/EbmlFloat.h
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Expand Up @@ -32,9 +32,9 @@ class EBML_DLL_API EbmlFloat : public EbmlElement {
return (GetSize() == 4 || GetSize() == 8);
}

filepos_t RenderData(IOCallback & output, bool bForceRender, bool bWithDefault = false) override;
filepos_t RenderData(IOCallback & output, bool bForceRender, ShouldWrite writeFilter = WriteSkipDefault) override;
filepos_t ReadData(IOCallback & input, ScopeMode ReadFully = SCOPE_ALL_DATA) override;
filepos_t UpdateSize(bool bWithDefault = false, bool bForceRender = false) override;
filepos_t UpdateSize(ShouldWrite writeFilter = WriteSkipDefault, bool bForceRender = false) override;

void SetPrecision(const EbmlFloat::Precision prec = FLOAT_32)
{
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6 changes: 3 additions & 3 deletions ebml/EbmlMaster.h
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Expand Up @@ -39,9 +39,9 @@ class EBML_DLL_API EbmlMaster : public EbmlElement {
*/
~EbmlMaster() override;

filepos_t RenderData(IOCallback & output, bool bForceRender, bool bWithDefault = false) override;
filepos_t RenderData(IOCallback & output, bool bForceRender, ShouldWrite writeFilter = WriteSkipDefault) override;
filepos_t ReadData(IOCallback & input, ScopeMode ReadFully) override;
filepos_t UpdateSize(bool bWithDefault = false, bool bForceRender = false) override;
filepos_t UpdateSize(ShouldWrite writeFilter = WriteSkipDefault, bool bForceRender = false) override;

bool PushElement(EbmlElement & element);
std::uint64_t GetSize() const override {
Expand Down Expand Up @@ -129,7 +129,7 @@ class EBML_DLL_API EbmlMaster : public EbmlElement {
/*!
\brief facility for Master elements to write only the head and force the size later
*/
filepos_t WriteHead(IOCallback & output, int SizeLength, bool bWithDefault = false);
filepos_t WriteHead(IOCallback & output, int SizeLength, ShouldWrite writeFilter = WriteSkipDefault);

void EnableChecksum(bool bIsEnabled = true) { bChecksumUsed = bIsEnabled; }
bool HasChecksum() const {return bChecksumUsed;}
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4 changes: 2 additions & 2 deletions ebml/EbmlSInteger.h
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Expand Up @@ -36,9 +36,9 @@ class EBML_DLL_API EbmlSInteger : public EbmlElement {
void SetDefaultSize(std::uint64_t nDefaultSize = DEFAULT_INT_SIZE) override {EbmlElement::SetDefaultSize(nDefaultSize); SetSize_(nDefaultSize);}

bool ValidateSize() const override {return GetSize() <= 8;}
filepos_t RenderData(IOCallback & output, bool bForceRender, bool bWithDefault = false) override;
filepos_t RenderData(IOCallback & output, bool bForceRender, ShouldWrite writeFilter = WriteSkipDefault) override;
filepos_t ReadData(IOCallback & input, ScopeMode ReadFully = SCOPE_ALL_DATA) override;
filepos_t UpdateSize(bool bWithDefault = false, bool bForceRender = false) override;
filepos_t UpdateSize(ShouldWrite writeFilter = WriteSkipDefault, bool bForceRender = false) override;

bool IsSmallerThan(const EbmlElement *Cmp) const override;

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4 changes: 2 additions & 2 deletions ebml/EbmlString.h
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Expand Up @@ -25,9 +25,9 @@ class EBML_DLL_API EbmlString : public EbmlElement {
explicit EbmlString(const EbmlCallbacks &, const std::string & aDefaultValue);

bool ValidateSize() const override {return GetSize() < 0x7FFFFFFF;} // any size is possible
filepos_t RenderData(IOCallback & output, bool bForceRender, bool bWithDefault = false) override;
filepos_t RenderData(IOCallback & output, bool bForceRender, ShouldWrite writeFilter = WriteSkipDefault) override;
filepos_t ReadData(IOCallback & input, ScopeMode ReadFully = SCOPE_ALL_DATA) override;
filepos_t UpdateSize(bool bWithDefault = false, bool bForceRender = false) override;
filepos_t UpdateSize(ShouldWrite writeFilter = WriteSkipDefault, bool bForceRender = false) override;

EbmlString & operator=(const std::string &);
using EbmlElement::operator const EbmlId &;
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4 changes: 2 additions & 2 deletions ebml/EbmlUInteger.h
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Expand Up @@ -34,9 +34,9 @@ class EBML_DLL_API EbmlUInteger : public EbmlElement {
void SetDefaultSize(std::uint64_t nDefaultSize = DEFAULT_UINT_SIZE) override {EbmlElement::SetDefaultSize(nDefaultSize); SetSize_(nDefaultSize);}

bool ValidateSize() const override {return GetSize() <= 8;}
filepos_t RenderData(IOCallback & output, bool bForceRender, bool bWithDefault = false) override;
filepos_t RenderData(IOCallback & output, bool bForceRender, ShouldWrite writeFilter = WriteSkipDefault) override;
filepos_t ReadData(IOCallback & input, ScopeMode ReadFully = SCOPE_ALL_DATA) override;
filepos_t UpdateSize(bool bWithDefault = false, bool bForceRender = false) override;
filepos_t UpdateSize(ShouldWrite writeFilter = WriteSkipDefault, bool bForceRender = false) override;

bool IsSmallerThan(const EbmlElement *Cmp) const override;

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4 changes: 2 additions & 2 deletions ebml/EbmlUnicodeString.h
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Expand Up @@ -71,9 +71,9 @@ class EBML_DLL_API EbmlUnicodeString : public EbmlElement {
explicit EbmlUnicodeString(const EbmlCallbacks &, const UTFstring & DefaultValue);

bool ValidateSize() const override {return true;} // any size is possible
filepos_t RenderData(IOCallback & output, bool bForceRender, bool bWithDefault = false) override;
filepos_t RenderData(IOCallback & output, bool bForceRender, ShouldWrite writeFilter = WriteSkipDefault) override;
filepos_t ReadData(IOCallback & input, ScopeMode ReadFully = SCOPE_ALL_DATA) override;
filepos_t UpdateSize(bool bWithDefault = false, bool bForceRender = false) override;
filepos_t UpdateSize(ShouldWrite writeFilter = WriteSkipDefault, bool bForceRender = false) override;

EbmlUnicodeString & operator=(const UTFstring &); ///< platform dependant code
using EbmlElement::operator const EbmlId &;
Expand Down
6 changes: 3 additions & 3 deletions ebml/EbmlVoid.h
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Expand Up @@ -23,17 +23,17 @@ DECLARE_EBML_BINARY(EbmlVoid)
/*!
\note overwrite to write fake data
*/
filepos_t RenderData(IOCallback & output, bool bForceRender, bool bWithDefault = false) override;
filepos_t RenderData(IOCallback & output, bool bForceRender, ShouldWrite writeFilter = WriteSkipDefault) override;

/*!
\brief Replace the void element content (written) with this one
*/
std::uint64_t ReplaceWith(EbmlElement & EltToReplaceWith, IOCallback & output, bool ComeBackAfterward = true, bool bWithDefault = false);
std::uint64_t ReplaceWith(EbmlElement & EltToReplaceWith, IOCallback & output, bool ComeBackAfterward = true, ShouldWrite writeFilter = WriteSkipDefault);

/*!
\brief Void the content of an element
*/
std::uint64_t Overwrite(const EbmlElement & EltToVoid, IOCallback & output, bool ComeBackAfterward = true, bool bWithDefault = false);
std::uint64_t Overwrite(const EbmlElement & EltToVoid, IOCallback & output, bool ComeBackAfterward = true, ShouldWrite writeFilter = WriteSkipDefault);

EBML_CONCRETE_CLASS(EbmlVoid)
};
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4 changes: 2 additions & 2 deletions src/EbmlBinary.cpp
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Expand Up @@ -50,7 +50,7 @@ EbmlBinary::~EbmlBinary() {
EbmlBinary::operator const binary &() const {return *Data;}


filepos_t EbmlBinary::RenderData(IOCallback & output, bool /* bForceRender */, bool /* bWithDefault */)
filepos_t EbmlBinary::RenderData(IOCallback & output, bool /* bForceRender */, ShouldWrite /* writeFilter */)
{
output.writeFully(Data,GetSize());

Expand All @@ -60,7 +60,7 @@ filepos_t EbmlBinary::RenderData(IOCallback & output, bool /* bForceRender */, b
/*!
\note no Default binary value handled
*/
std::uint64_t EbmlBinary::UpdateSize(bool /* bWithDefault */, bool /* bForceRender */)
std::uint64_t EbmlBinary::UpdateSize(ShouldWrite /* writeFilter */, bool /* bForceRender */)
{
return GetSize();
}
Expand Down
4 changes: 2 additions & 2 deletions src/EbmlCrc32.cpp
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Expand Up @@ -161,7 +161,7 @@ void EbmlCrc32::AddElementCRC32(EbmlElement &ElementToCRC)
{
// Use a special IOCallback class that Render's to memory instead of to disk
MemIOCallback memoryBuffer;
ElementToCRC.Render(memoryBuffer, true, true);
ElementToCRC.Render(memoryBuffer, WriteAll, true);

const std::uint64_t memSize = memoryBuffer.GetDataBufferSize();
if (memSize > std::numeric_limits<std::uint32_t>::max())
Expand All @@ -183,7 +183,7 @@ bool EbmlCrc32::CheckElementCRC32(EbmlElement &ElementToCRC) const
return CheckCRC(m_crc_final, memoryBuffer.GetDataBuffer(), static_cast<std::uint32_t>(memSize));
}

filepos_t EbmlCrc32::RenderData(IOCallback & output, bool /* bForceRender */, bool /* bWithDefault */)
filepos_t EbmlCrc32::RenderData(IOCallback & output, bool /* bForceRender */, ShouldWrite /* writeFilter */)
{
filepos_t Result = 4;

Expand Down
2 changes: 1 addition & 1 deletion src/EbmlDate.cpp
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Expand Up @@ -31,7 +31,7 @@ filepos_t EbmlDate::ReadData(IOCallback & input, ScopeMode ReadFully)
return GetSize();
}

filepos_t EbmlDate::RenderData(IOCallback & output, bool /* bForceRender */, bool /* bWithDefault */)
filepos_t EbmlDate::RenderData(IOCallback & output, bool /* bForceRender */, ShouldWrite /* writeFilter */)
{
assert(GetSize() == 8 || GetSize() == 0);
if (GetSize() == 8) {
Expand Down
26 changes: 13 additions & 13 deletions src/EbmlElement.cpp
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Expand Up @@ -475,18 +475,18 @@ EbmlElement *EbmlElement::CreateElementUsingContext(const EbmlId & aID, const Eb
/*!
\todo verify that the size written is the same as the data written
*/
filepos_t EbmlElement::Render(IOCallback & output, bool bWithDefault, bool bKeepPosition, bool bForceRender)
filepos_t EbmlElement::Render(IOCallback & output, ShouldWrite writeFilter, bool bKeepPosition, bool bForceRender)
{
assert(bValueIsSet || (bWithDefault && DefaultISset())); // an element is been rendered without a value set !!!
assert(bValueIsSet || writeFilter(*this)); // an element is been rendered without a value set !!!
// it may be a mandatory element without a default value
if (!bWithDefault && IsDefaultValue()) {
if (!writeFilter(*this)) {
return 0;
}
#if !defined(NDEBUG)
std::uint64_t SupposedSize = UpdateSize(bWithDefault, bForceRender);
std::uint64_t SupposedSize = UpdateSize(writeFilter, bForceRender);
#endif // !NDEBUG
filepos_t result = RenderHead(output, bForceRender, bWithDefault, bKeepPosition);
const std::uint64_t WrittenSize = RenderData(output, bForceRender, bWithDefault);
filepos_t result = RenderHead(output, bForceRender, writeFilter, bKeepPosition);
const std::uint64_t WrittenSize = RenderData(output, bForceRender, writeFilter);
#if !defined(NDEBUG)
if (static_cast<std::int64_t>(SupposedSize) != (0-1))
assert(WrittenSize == SupposedSize);
Expand All @@ -500,12 +500,12 @@ filepos_t EbmlElement::Render(IOCallback & output, bool bWithDefault, bool bKeep
\todo handle exceptions on errors
\todo handle CodeSize bigger than 5 bytes
*/
filepos_t EbmlElement::RenderHead(IOCallback & output, bool bForceRender, bool bWithDefault, bool bKeepPosition)
filepos_t EbmlElement::RenderHead(IOCallback & output, bool bForceRender, ShouldWrite writeFilter, bool bKeepPosition)
{
if (EBML_ID_LENGTH((const EbmlId&)*this) <= 0 || EBML_ID_LENGTH((const EbmlId&)*this) > 4)
return 0;

UpdateSize(bWithDefault, bForceRender);
UpdateSize(writeFilter, bForceRender);

return MakeRenderHead(output, bKeepPosition);
}
Expand All @@ -531,9 +531,9 @@ filepos_t EbmlElement::MakeRenderHead(IOCallback & output, bool bKeepPosition)
return FinalHeadSize;
}

std::uint64_t EbmlElement::ElementSize(bool bWithDefault) const
std::uint64_t EbmlElement::ElementSize(ShouldWrite writeFilter) const
{
if (!bWithDefault && IsDefaultValue())
if (!writeFilter(*this))
return 0; // won't be saved
return Size + EBML_ID_LENGTH((const EbmlId&)*this) + CodedSizeLength(Size, SizeLength, bSizeIsFinite);
}
Expand Down Expand Up @@ -602,21 +602,21 @@ filepos_t EbmlElement::OverwriteData(IOCallback & output, bool bKeepPosition)

auto CurrentPosition = output.getFilePointer();
output.setFilePointer(GetElementPosition() + HeaderSize);
auto Result = RenderData(output, true, bKeepPosition);
auto Result = RenderData(output, true, bKeepPosition ? WriteAll : WriteSkipDefault);
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I don't understand the intent behind this change. What does keeping the position have to do with the question whether or not to write the element?

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This is just the translation of the previous call into the new system. bKeepPosition would be used as the bWithDefault value. So if it's true it writes elements even if they are the default value (WriteAll), if it's false it only writes the elements if they are not the default value (SkipDefault).

The original logic may be flawed and it should be fixed separately. In fact when overwriting you'd probably want to tell which elements you want to write (the least possible).

This whole API is a recipe for broken files (which originally was a welcome possibility in libebml to be able to generate broken files to test against). It seems mkvtoolnix doesn't use it, there's only a test calling OverwriteHead(). So I'd rather remove the API altogether.

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Ah, I see. Thanks for the explanation. Yeah, MKVToolNix (or rather: mkvpropedit) only uses OverwriteHead for cases where it has to cover a one-byte space that's suddenly left by other operations; in such a case it forces the element size field to be one byte longer than necessary.

It never uses OverwriteData, though. If it has to overwrite a whole element, I think it simply uses Render & sets the file position manually.

output.setFilePointer(CurrentPosition);
assert(Result == DataSize);
return Result;
}


std::uint64_t EbmlElement::VoidMe(IOCallback & output, bool bWithDefault) const
std::uint64_t EbmlElement::VoidMe(IOCallback & output, ShouldWrite writeFilter) const
{
if (ElementPosition == 0) {
return 0; // the element has not been written
}

EbmlVoid Dummy;
return Dummy.Overwrite(*this, output, true, bWithDefault);
return Dummy.Overwrite(*this, output, true, writeFilter);
}

} // namespace libebml
6 changes: 3 additions & 3 deletions src/EbmlFloat.cpp
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Expand Up @@ -51,7 +51,7 @@ EbmlFloat & EbmlFloat::SetValue(double NewValue) {
\todo handle exception on errors
\todo handle 10 bits precision
*/
filepos_t EbmlFloat::RenderData(IOCallback & output, bool /* bForceRender */, bool /* bWithDefault */)
filepos_t EbmlFloat::RenderData(IOCallback & output, bool /* bForceRender */, ShouldWrite /* writeFilter */)
{
assert(GetSize() == 4 || GetSize() == 8);

Expand All @@ -74,9 +74,9 @@ filepos_t EbmlFloat::RenderData(IOCallback & output, bool /* bForceRender */, bo
return GetSize();
}

std::uint64_t EbmlFloat::UpdateSize(bool bWithDefault, bool /* bForceRender */)
std::uint64_t EbmlFloat::UpdateSize(ShouldWrite writeFilter, bool /* bForceRender */)
{
if (!bWithDefault && IsDefaultValue())
if (!writeFilter(*this))
return 0;
return GetSize();
}
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