Text layout - first part

PdfForQtLib/sources/pdftextlayout.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 PDFTEXTLAYOUT_H
+#define PDFTEXTLAYOUT_H
+
+#include "pdfglobal.h"
+
+#include <QPainterPath>
+
+#include <set>
+
+namespace pdf
+{
+
+struct PDFTextCharacterInfo
+{
+    /// Character
+    QChar character;
+
+    /// Character path
+    QPainterPath outline;
+
+    /// Do we use a vertical writing system?
+    bool isVerticalWritingSystem = false;
+
+    /// Advance (in character space, it must be translated
+    /// into device space), for both vertical/horizontal modes.
+    PDFReal advance = 0.0;
+
+    /// Font size (in character space, it must be translated
+    /// into device space)
+    PDFReal fontSize = 0.0;
+
+    /// Transformation matrix from character space to device space
+    QMatrix matrix;
+};
+
+struct PDFTextLayoutSettings
+{
+    /// Number of samples for 'docstrum' algorithm, i.e. number of
+    /// nearest characters. By default, 5 characters should fit.
+    size_t samples = 5;
+
+    /// Distance sensitivity to determine, if characters are close enough.
+    /// Maximal distance is computed as current character advance multiplied
+    /// by this constant.
+    PDFReal distanceSensitivity = 4.0;
+
+    /// Maximal vertical distance, in portion of font size, of two characters
+    /// to be considered they lie on same line.
+    PDFReal charactersOnLineSensitivity = 0.25;
+
+    /// Maximal ratio between font size of characters to be considered
+    /// that they lie on same line.
+    PDFReal fontSensitivity = 2.0;
+
+    /// Maximal space ratio between two lines of block. Default coefficient
+    /// means, that height ratio limit is (height1 + height2)
+    PDFReal blockVerticalSensitivity = 1.5;
+
+    /// Minimal horizontal overlap for two lines considered to be in one block
+    PDFReal blockOverlapSensitivity = 0.3;
+};
+
+/// Represents character in device space coordinates. All values (dimensions,
+/// bounding box, etc. are in device space coordinates).
+struct TextCharacter
+{
+    QChar character;
+    QPointF position;
+    PDFReal angle = 0.0;
+    PDFReal fontSize = 0.0;
+    PDFReal advance = 0.0;
+    QPainterPath boundingBox;
+};
+
+using TextCharacters = std::vector<TextCharacter>;
+
+/// Represents text line consisting of set of characters and line bounding box.
+class PDFTextLine
+{
+public:
+    /// Construct new line from characters. Characters are sorted in x-coordinate
+    /// and bounding box is computed.
+    /// \param characters
+    explicit PDFTextLine(TextCharacters characters);
+
+    const TextCharacters& getCharacters() const { return m_characters; }
+    const QPainterPath& getBoundingBox() const { return m_boundingBox; }
+
+private:
+    TextCharacters m_characters;
+    QPainterPath m_boundingBox;
+};
+
+using PDFTextLines = std::vector<PDFTextLine>;
+
+/// Represents text block consisting of set of lines and block bounding box.
+class PDFTextBlock
+{
+public:
+    explicit inline PDFTextBlock(PDFTextLines textLines);
+
+    const PDFTextLines& getLines() const { return m_lines; }
+    const QPainterPath& getBoundingBox() const { return m_boundingBox; }
+
+private:
+    PDFTextLines m_lines;
+    QPainterPath m_boundingBox;
+};
+
+using PDFTextBlocks = std::vector<PDFTextBlock>;
+
+/// Text layout of single page. Can handle various fonts, various angles of lines
+/// and vertically oriented text. It performs the "docstrum" algorithm.
+class PDFTextLayout
+{
+public:
+    explicit PDFTextLayout();
+
+    /// Adds character to the layout
+    void addCharacter(const PDFTextCharacterInfo& info);
+
+    /// Perorms text layout algorithm
+    void perform();
+
+    /// Optimizes layout memory allocation to contain less space
+    void optimize();
+
+    /// Returns estimate of number of bytes, which this mesh occupies in memory
+    qint64 getMemoryConsumptionEstimate() const;
+
+private:
+
+    /// Makes layout for particular angle
+    void performDoLayout(PDFReal angle);
+
+    /// Returns a list of characters for particular angle. Exact match is used
+    /// for angle, even if angle is floating point number.
+    /// \param angle Angle
+    TextCharacters getCharactersForAngle(PDFReal angle) const;
+
+    /// Applies transform to text characters (positions and bounding boxes)
+    /// \param characters Characters
+    /// \param matrix Transform matrix
+    void applyTransform(TextCharacters& characters, const QMatrix& matrix);
+
+    TextCharacters m_characters;
+    std::set<PDFReal> m_angles;
+    PDFTextLayoutSettings m_settings;
+};
+
+}   // namespace pdf
+
+#endif // PDFTEXTLAYOUT_H