Generalize previews: Add PreviewGenerator*

gui/previewgeneratorpdf.h

@@ -0,0 +1,24 @@
+#ifndef PREVIEWGENERATORPDF_H
+#define PREVIEWGENERATORPDF_H
+#include <poppler-qt5.h>
+#include "previewgenerator.h"
+#include "previewresultpdf.h"
+
+class PreviewGeneratorPdf : public PreviewGenerator
+{
+  protected:
+	QHash<QString, Poppler::Document *> documentcache;
+	Poppler::Document *document(QString path);
+
+  public:
+	using PreviewGenerator::PreviewGenerator;
+
+	PreviewResult *generate(RenderConfig config, QString documentPath, unsigned int page);
+
+	~PreviewGeneratorPdf()
+	{
+		qDeleteAll(documentcache);
+	}
+};
+
+#endif // PREVIEWGENERATORPDF_H