Color spaces, beginning of painting

PdfForQtLib/sources/pdfflatarray.h

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+//    Copyright (C) 2019 Jakub Melka
+//
+//    This file is part of PdfForQt.
+//
+//    PdfForQt is free software: you can redistribute it and/or modify
+//    it under the terms of the GNU Lesser General Public License as published by
+//    the Free Software Foundation, either version 3 of the License, or
+//    (at your option) any later version.
+//
+//    PdfForQt is distributed in the hope that it will be useful,
+//    but WITHOUT ANY WARRANTY; without even the implied warranty of
+//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//    GNU Lesser General Public License for more details.
+//
+//    You should have received a copy of the GNU Lesser General Public License
+//    along with PDFForQt.  If not, see <https://www.gnu.org/licenses/>.
+
+
+#ifndef PDFFLATARRAY_H
+#define PDFFLATARRAY_H
+
+#include <QtGlobal>
+
+#include <array>
+#include <vector>
+#include <algorithm>
+
+namespace pdf
+{
+
+/// This represents a fast array, consisting of "fast" block of fixed size \p FlatSize,
+/// and "slow" block of variable size. Usually, this array is used when vast majority
+/// of usage size is below FlatSize, only minority is above FlatSize. Typical example
+/// of use of this class:
+///
+/// We have colors in PDF, which can have usually 1, 3 or 4 color components. But in some
+/// rare cases, we have much more components, for example for DeviceN color spaces.
+/// For this reason, we will set FlatSize to 4 (so Gray, RGB and CMYK colors will not
+/// use slow "variable" part).
+template<typename T, size_t FlatSize>
+class PDFFlatArray
+{
+public:
+    explicit PDFFlatArray() :
+        m_flatBlock(),
+        m_flatBlockEndIterator(m_flatBlock.begin()),
+        m_variableBlock()
+    {
+
+    }
+
+    template<typename... Arguments, typename std::enable_if<sizeof...(Arguments) < FlatSize, int>::type = 0>
+    explicit inline PDFFlatArray(Arguments... arguments) :
+        m_flatBlock(arguments...),
+        m_flatBlockEndIterator(std::next(m_flatBlock.begin(), sizeof...(Arguments))),
+        m_variableBlock()
+    {
+
+    }
+
+    /// Returns the size of the array
+    size_t size() const { return getFlatBlockSize() + m_variableBlock.size(); }
+
+    /// Returns true, if array is empty
+    bool empty() const { return size() == 0; }
+
+    template<size_t index>
+    const T& get() const
+    {
+        if constexpr (index < FlatSize)
+        {
+            return m_flatBlock[size];
+        }
+        else
+        {
+            return m_variableBlock[size - FlatSize];
+        }
+    }
+
+    template<size_t index>
+    T& get()
+    {
+        if constexpr (index < FlatSize)
+        {
+            return m_flatBlock[size];
+        }
+        else
+        {
+            return m_variableBlock[size - FlatSize];
+        }
+    }
+
+    const T& operator[] (size_t index) const
+    {
+        Q_ASSERT(index < size());
+
+        if (index < FlatSize)
+        {
+            return m_flatBlock[index];
+        }
+        else
+        {
+            return m_variableBlock[index - FlatSize];
+        }
+    }
+
+private:
+    size_t getFlatBlockSize() const { return std::distance(m_flatBlock.cbegin(), std::array<T, FlatSize>::const_iterator(m_flatBlockEndIterator)); }
+
+    std::array<T, FlatSize> m_flatBlock;
+    typename std::array<T, FlatSize>::iterator m_flatBlockEndIterator; ///< Pointer to the end of flat block
+    std::vector<T> m_variableBlock;
+};
+
+}   // namespace pdf
+
+#endif // PDFFLATARRAY_H