add new presentation mode for PDF export

This commit adds a new PDF export mode, called "presentation", similar
to what we get from a LaTeX-Beamer document (or Powerpoint).  When
exporting to this mode, each xournalpp page will be rendered to as
many pdf pages as there are layers on the xournalpp page. First, Layer
1 is rendered, then Layer 1 + Layer 2, etc. until all layers are
rendered.

It is accessible by selecting "Save as" in the File menu, and choosing
a PDF export. Then a specific box has to be checked in the Export
Dialog.

Exporting to presentation mode can also be done with the command-line
flag "--export-presentation". For instance:

xournalpp -p output.pdf --export-presentation file.xopp

src/control/XournalMain.cpp

@@ -52,7 +52,8 @@ auto migrateSettings() -> MigrateResult;
 void checkForErrorlog();
 void checkForEmergencySave(Control* control);
 
-auto exportPdf(const char* input, const char* output, const char* range, bool noBackground) -> int;
+auto exportPdf(const char* input, const char* output, const char* range, bool noBackground, bool presentationMode)
+        -> int;
 auto exportImg(const char* input, const char* output, const char* range, int pngDpi, int pngWidth, int pngHeight,
                bool noBackground) -> int;
 
@@ -301,10 +302,13 @@ auto exportImg(const char* input, const char* output, const char* range, int png
  * @param output Path to the output file
  * @param range Page range to be parsed. If range=nullptr, exports the whole file
  * @param noBackground If true, the exported pdf file has white background
+ * @param presentationMode If true, then for each xournalpp page, instead of rendering one PDF page, the page layers are
+ * rendered one by one to produce as many pages as there are layers.
  *
  * @return 0 on success, -2 on failure opening the input file, -3 on export failure
  */
-auto exportPdf(const char* input, const char* output, const char* range, bool noBackground) -> int {
+auto exportPdf(const char* input, const char* output, const char* range, bool noBackground, bool presentationMode)
+        -> int {
     LoadHandler loader;
 
     Document* doc = loader.loadDocument(input);
@@ -327,14 +331,14 @@ auto exportPdf(const char* input, const char* output, const char* range, bool no
         // Parse the range
         PageRangeVector exportRange = PageRange::parse(range, doc->getPageCount());
         // Do the export
-        exportSuccess = pdfe->createPdf(path, exportRange);
+        exportSuccess = pdfe->createPdf(path, exportRange, presentationMode);
         // Clean up
         for (PageRangeEntry* e: exportRange) {
             delete e;
         }
         exportRange.clear();
     } else {
-        exportSuccess = pdfe->createPdf(path);
+        exportSuccess = pdfe->createPdf(path, presentationMode);
     }
 
     if (!exportSuccess) {
@@ -370,7 +374,10 @@ struct XournalMainPrivate {
     int exportPngDpi = -1;
     int exportPngWidth = -1;
     int exportPngHeight = -1;
-    bool exportNoBackground = false;
+    gboolean exportNoBackground =
+            false;  // don't use bool, see
+                    // https://stackoverflow.com/questions/21152042/is-glib-command-line-parsing-order-sensitive
+    gboolean presentationMode = false;
     std::unique_ptr<GladeSearchpath> gladePath;
     std::unique_ptr<Control> control;
     std::unique_ptr<MainWindow> win;
@@ -577,7 +584,7 @@ auto on_handle_local_options(GApplication*, GVariantDict*, XMPtr app_data) -> gi
 
     if (app_data->pdfFilename && app_data->optFilename && *app_data->optFilename) {
         return exportPdf(*app_data->optFilename, app_data->pdfFilename, app_data->exportRange,
-                         app_data->exportNoBackground);
+                         app_data->exportNoBackground, app_data->presentationMode);
     }
     if (app_data->imgFilename && app_data->optFilename && *app_data->optFilename) {
         return exportImg(*app_data->optFilename, app_data->imgFilename, app_data->exportRange, app_data->exportPngDpi,
@@ -631,6 +638,11 @@ auto XournalMain::run(int argc, char** argv) -> int {
                            "                                 The exported file has transparent or white background,\n"
                            "                                 depending on what its format supports\n"),
                          0},
+            GOptionEntry{"export-presentation", 0, 0, G_OPTION_ARG_NONE, &app_data.presentationMode,
+                         _("Export in presentation mode\n"
+                           "                                 In PDF export, layers are rendered one by one,\n"
+                           "                                 suitable for presentation\n"),
+                         0},
             GOptionEntry{"export-range", 0, 0, G_OPTION_ARG_STRING, &app_data.exportRange,
                          _("Only export the pages specified by RANGE (e.g. \"2-3,5,7-\")\n"
                            "                                 No effect without -p/--create-pdf or -i/--create-img"),

src/control/jobs/BaseExportJob.cpp

@@ -68,7 +68,7 @@ auto BaseExportJob::showFilechooser() -> bool {
             gtk_widget_destroy(dialog);
             return false;
         }
-        auto file =  Util::fromGFilename(gtk_file_chooser_get_filename(GTK_FILE_CHOOSER(dialog)));
+        auto file = Util::fromGFilename(gtk_file_chooser_get_filename(GTK_FILE_CHOOSER(dialog)));
         Util::clearExtensions(file);
         // Since we add the extension after the OK button, we have to check manually on existing files
         if (testAndSetFilepath(std::move(file)) && control->askToReplace(this->filepath)) {
@@ -85,7 +85,7 @@ auto BaseExportJob::showFilechooser() -> bool {
 
 auto BaseExportJob::testAndSetFilepath(fs::path file) -> bool {
     try {
-        if(fs::is_directory(file.parent_path())){
+        if (fs::is_directory(file.parent_path())) {
             this->filepath = std::move(file);
             return true;
         }

src/control/jobs/CustomExportJob.cpp

@@ -75,7 +75,7 @@ auto CustomExportJob::showFilechooser() -> bool {
     doc->lock();
     auto* dlg = new ExportDialog(control->getGladeSearchPath());
     if (filepath.extension() == ".pdf") {
-        dlg->removeQualitySetting();
+        dlg->showPresentationMode();
         format = EXPORT_GRAPHICS_PDF;
     } else if (filepath.extension() == ".svg") {
         dlg->removeQualitySetting();
@@ -94,6 +94,7 @@ auto CustomExportJob::showFilechooser() -> bool {
     }
 
     exportRange = dlg->getRange();
+    presentationMode = dlg->presentationMode();
 
     if (format == EXPORT_GRAPHICS_PNG) {
         pngQualityParameter = dlg->getPngQualityParameter();
@@ -142,7 +143,7 @@ void CustomExportJob::run() {
 
         pdfe->setNoBackgroundExport(filters[this->chosenFilterName]->withoutBackground);
 
-        if (!pdfe->createPdf(this->filepath, exportRange)) {
+        if (!pdfe->createPdf(this->filepath, exportRange, presentationMode)) {
             this->errorMsg = pdfe->getLastError();
         }
 

src/control/jobs/CustomExportJob.h

@@ -67,6 +67,11 @@ private:
      */
     bool exportTypeXoj = false;
 
+    /**
+     * Export Layers as pages
+     */
+    bool presentationMode = false;
+
     string lastError;
 
     string chosenFilterName;

src/control/jobs/PdfExportJob.cpp

@@ -32,7 +32,7 @@ void PdfExportJob::run() {
     XojPdfExport* pdfe = XojPdfExportFactory::createExport(doc, control);
     doc->unlock();
 
-    if (!pdfe->createPdf(this->filepath)) {
+    if (!pdfe->createPdf(this->filepath, false)) {
         if (control->getWindow()) {
             callAfterRun();
         } else {

src/gui/dialog/ExportDialog.cpp

@@ -8,6 +8,7 @@
 ExportDialog::ExportDialog(GladeSearchpath* gladeSearchPath):
         GladeGui(gladeSearchPath, "exportSettings.glade", "exportDialog") {
 
+    gtk_widget_hide(get("cbPresentationMode"));
     g_signal_connect(get("rdRangePages"), "toggled", G_CALLBACK(+[](GtkToggleButton* togglebutton, ExportDialog* self) {
                          gtk_widget_set_sensitive(self->get("txtPages"), gtk_toggle_button_get_active(togglebutton));
                      }),
@@ -44,6 +45,11 @@ void ExportDialog::removeQualitySetting() {
     gtk_widget_hide(get("cbQuality"));
 }
 
+void ExportDialog::showPresentationMode() {
+    gtk_widget_show(get("cbPresentationMode"));
+    removeQualitySetting();
+}
+
 void ExportDialog::selectQualityCriterion(GtkComboBox* comboBox, ExportDialog* self) {
     int activeCriterion = gtk_combo_box_get_active(comboBox);
     switch (activeCriterion) {
@@ -70,6 +76,10 @@ auto ExportDialog::getPngQualityParameter() -> RasterImageQualityParameter {
 
 auto ExportDialog::isConfirmed() const -> bool { return this->confirmed; }
 
+auto ExportDialog::presentationMode() -> bool {
+    return gtk_toggle_button_get_active(GTK_TOGGLE_BUTTON(get("cbPresentationMode")));
+}
+
 auto ExportDialog::getRange() -> PageRangeVector {
     GtkWidget* rdRangeCurrent = get("rdRangeCurrent");
     GtkWidget* rdRangePages = get("rdRangePages");

src/gui/dialog/ExportDialog.h

@@ -27,6 +27,7 @@ public:
     void initPages(int current, int count);
     bool isConfirmed() const;
     PageRangeVector getRange();
+    bool presentationMode();
 
     /**
      * @brief Reads the quality parameter from the dialog
@@ -40,6 +41,12 @@ public:
      */
     void removeQualitySetting();
 
+    /**
+     * @brief Show "presentation mode" checkbox and hide quality settings
+     * (both cannot be shown at the same time)
+     */
+    void showPresentationMode();
+
     /**
      * @brief Handler for changes in combobox cbQuality
      */

src/pdf/base/XojCairoPdfExport.cpp

@@ -1,5 +1,6 @@
 #include "XojCairoPdfExport.h"
 
+#include <map>
 #include <sstream>
 #include <stack>
 
@@ -119,7 +120,29 @@ void XojCairoPdfExport::exportPage(size_t page) {
     cairo_restore(this->cr);
 }
 
-auto XojCairoPdfExport::createPdf(fs::path const& file, PageRangeVector& range) -> bool {
+// export layers one by one to produce as many PDF pages as there are layers.
+void XojCairoPdfExport::exportPageLayers(size_t page) {
+    PageRef p = doc->getPage(page);
+
+    // We keep a copy of the layers initial Visible state
+    std::map<Layer*, bool> initialVisibility;
+    for (const auto& layer: *p->getLayers()) {
+        initialVisibility[layer] = layer->isVisible();
+        layer->setVisible(false);
+    }
+
+    // We draw as many pages as there are layers. The first page has
+    // only Layer 1 visible, the last has all layers visible.
+    for (const auto& layer: *p->getLayers()) {
+        layer->setVisible(true);
+        exportPage(page);
+    }
+
+    // We restore the initial visibilities
+    for (const auto& layer: *p->getLayers()) layer->setVisible(initialVisibility[layer]);
+}
+
+auto XojCairoPdfExport::createPdf(fs::path const& file, PageRangeVector& range, bool presentationMode) -> bool {
     if (range.empty()) {
         this->lastError = _("No pages to export!");
         return false;
@@ -145,7 +168,11 @@ auto XojCairoPdfExport::createPdf(fs::path const& file, PageRangeVector& range)
                 continue;
             }
 
-            exportPage(i);
+            if (presentationMode) {
+                exportPageLayers(i);
+            } else {
+                exportPage(i);
+            }
 
             if (this->progressListener) {
                 this->progressListener->setCurrentState(c++);
@@ -157,7 +184,7 @@ auto XojCairoPdfExport::createPdf(fs::path const& file, PageRangeVector& range)
     return true;
 }
 
-auto XojCairoPdfExport::createPdf(fs::path const& file) -> bool {
+auto XojCairoPdfExport::createPdf(fs::path const& file, bool presentationMode) -> bool {
     if (doc->getPageCount() < 1) {
         lastError = _("No pages to export!");
         return false;
@@ -173,7 +200,12 @@ auto XojCairoPdfExport::createPdf(fs::path const& file) -> bool {
     }
 
     for (int i = 0; i < count; i++) {
-        exportPage(i);
+
+        if (presentationMode) {
+            exportPageLayers(i);
+        } else {
+            exportPage(i);
+        }
 
         if (this->progressListener) {
             this->progressListener->setCurrentState(i);

src/pdf/base/XojCairoPdfExport.h

@@ -23,8 +23,8 @@ public:
     virtual ~XojCairoPdfExport();
 
 public:
-    virtual bool createPdf(fs::path const& file);
-    virtual bool createPdf(fs::path const& file, PageRangeVector& range);
+    virtual bool createPdf(fs::path const& file, bool presentationMode);
+    virtual bool createPdf(fs::path const& file, PageRangeVector& range, bool presentationMode);
     virtual string getLastError();
 
     /**
@@ -47,6 +47,10 @@ private:
 #endif
     void endPdf();
     void exportPage(size_t page);
+    /**
+     * Export as a PDF document where each additional layer creates a
+     * new page */
+    void exportPageLayers(size_t page);
 
 private:
     Document* doc = nullptr;

src/pdf/base/XojPdfExport.h

@@ -24,8 +24,8 @@ public:
     virtual ~XojPdfExport();
 
 public:
-    virtual bool createPdf(fs::path const& file) = 0;
-    virtual bool createPdf(fs::path const& file, PageRangeVector& range) = 0;
+    virtual bool createPdf(fs::path const& file, bool presentationMode) = 0;
+    virtual bool createPdf(fs::path const& file, PageRangeVector& range, bool presentationMode) = 0;
     virtual string getLastError() = 0;
 
     /**

ui/exportSettings.glade

@@ -328,6 +328,24 @@ Set export parameters</property>
                     <property name="top-attach">0</property>
                   </packing>
                 </child>
+
+		<child>
+                  <object class="GtkCheckButton" id="cbPresentationMode">
+                    <property name="label" translatable="yes">Export as a presentation</property>
+                    <property name="visible">True</property>
+                    <property name="can_focus">True</property>
+                    <property name="receives_default">False</property>
+                    <property name="tooltip_text" translatable="yes">If enabled, the layers of each page will be added one by one. The resulting PDF file can be used for a presentation.</property>
+                    <property name="draw_indicator">True</property>
+                  </object>
+                  <packing>
+		    <!-- Same place as "Image quality"; only one of them is shown -->
+                    <property name="left_attach">0</property>
+                    <property name="top_attach">0</property>
+                    <property name="width">3</property>
+                  </packing>
+                </child>
+
                 <child>
                   <placeholder/>
                 </child>