Improving WPF Text Display Performance

ReadFileFragment.cpp

HRESULT FontFileStream::ReadFileFragment(const void ** fragmentStart, UINT64 fileOffset, UINT64 fragmentSize, void ** fragmentContext)
{
	if (fragmentStart != nullptr)
		*fragmentStart = nullptr;
	if (fragmentContext != nullptr)
		*fragmentContext = nullptr;
	if (fragmentStart == nullptr || fragmentContext == nullptr)
		return E_POINTER;
	if (fileOffset >= m_length || fileOffset + fragmentSize > m_length)
		return E_INVALIDARG;

	// return a pointer into the memory-mapped font bundle
	*fragmentStart = static_cast<const void *>(m_data + fileOffset);
	return S_OK;
}