Snapper, some code for screenshot tool

PdfForQtLib/sources/pdfsnapper.h

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+//    Copyright (C) 2020 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 PDFSNAPPER_H
+#define PDFSNAPPER_H
+
+#include "pdfglobal.h"
+
+#include <array>
+
+class QPainter;
+
+namespace pdf
+{
+class PDFPrecompiledPage;
+
+enum class SnapType
+{
+    Invalid,
+    PageCorner,        ///< Corner of the page media box
+    ImageCorner,       ///< Corner of image
+    PageCenter,        ///< Center of page media box
+    ImageCenter,       ///< Center of image
+    LineCenter,        ///< Center of line
+    GeneratedLineProjection    ///< Generated point to line projections
+};
+
+/// Contain informations for snap points in the pdf page. Snap points
+/// can be for example image centers, rectangle corners, line start/end
+/// points, page boundary boxes etc. All coordinates are in page coordinates.
+class PDFSnapInfo
+{
+public:
+    explicit inline PDFSnapInfo() = default;
+
+    struct SnapPoint
+    {
+        explicit inline constexpr SnapPoint() = default;
+        explicit inline constexpr SnapPoint(SnapType type, QPointF point) :
+            type(type),
+            point(point)
+        {
+
+        }
+
+        SnapType type = SnapType::Invalid;
+        QPointF point;
+    };
+
+    /// Adds page media box. Media box must be in page coordinates.
+    /// \param mediaBox Media box
+    void addPageMediaBox(const QRectF& mediaBox);
+
+    /// Adds image box. Because it is not guaranteed, that it will be rectangle, five
+    /// points are defined - four corners and center.
+    /// \param points Four corner points in clockwise order, fifth point is center,
+    ///        all in page coordinates.
+    void addImage(const std::array<QPointF, 5>& points);
+
+    /// Adds line and line center points
+    /// \param start Start point of line, in page coordinates
+    /// \param end End point of line, in page coordinates
+    void addLine(const QPointF& start, const QPointF& end);
+
+    /// Returns snap points
+    const std::vector<SnapPoint>& getSnapPoints() const { return m_snapPoints; }
+
+private:
+    std::vector<SnapPoint> m_snapPoints;
+    std::vector<QLineF> m_snapLines;
+};
+
+/// Snap engine, which handles snapping of points on the page.
+class PDFSnapper
+{
+public:
+    PDFSnapper();
+
+    /// Draws snapping points onto the page
+    /// \param painter Painter
+    /// \param pageIndex Page index
+    /// \param compiledPage Compiled page
+    /// \param pagePointToDevicePointMatrix Matrix mapping page space to device point space
+    void drawSnapPoints(QPainter* painter,
+                        pdf::PDFInteger pageIndex,
+                        const PDFPrecompiledPage* compiledPage,
+                        const QMatrix& pagePointToDevicePointMatrix) const;
+
+private:
+    PDFSnapInfo m_currentPageSnapInfo;
+    PDFInteger m_currentPage = -1;
+};
+
+}   // namespace pdf
+
+#endif // PDFSNAPPER_H