Printing: Use FPDF_RenderPage instead of FPDF_RenderPageBitmap to allow vector graphics

2026-08-10 18:35:49 +02:00
parent f13a836ebd
commit 20b19775b1
6 changed files with 365 additions and 118 deletions
@@ -0,0 +1,94 @@
+using System;
+using System.IO;
+using System.Printing;
+
+namespace Elwig.Helpers.Printing {
+    public class PdfPrinter {
+
+        public string PrinterName { get; init; }
+
+        public PdfPrinter(string? printerName = null) {
+            PrinterName = printerName ?? GetDefaultPrinterName() ?? throw new InvalidOperationException("No default Windows printer is configured.");
+        }
+
+        public void Print(string pdfPath, int copies = 1, bool doublePaged = false) {
+            if (!File.Exists(pdfPath)) throw new FileNotFoundException("PDF file not found.", pdfPath);
+
+            IntPtr document = PdfiumNative.FPDF_LoadDocument(pdfPath, null);
+            if (document == IntPtr.Zero) throw new InvalidOperationException("PDFium could not open the PDF.");
+
+            try {
+                int pageCount = PdfiumNative.FPDF_GetPageCount(document);
+                if (pageCount <= 0)
+                    return;
+
+                using var printer = new Win32Printer.Printer(PrinterName);
+                printer.TrySetDuplex(doublePaged ? Duplexing.TwoSidedLongEdge : Duplexing.OneSided);
+                for (int i = 0; i < copies; i++) {
+                    printer.StartDocument(Path.GetFileName(pdfPath));
+                    bool documentStarted = true;
+                    try {
+                        for (int j = 0; j < pageCount; j++) {
+                            PrintPage(document, printer, j);
+                        }
+                        printer.EndDocument();
+                        documentStarted = false;
+                    } finally {
+                        if (documentStarted) printer.AbortDocument();
+                    }
+                }
+            } finally {
+                PdfiumNative.FPDF_CloseDocument(document);
+            }
+        }
+
+        private static void PrintPage(IntPtr document, Win32Printer.Printer printer, int pageIndex) {
+            if (!PdfiumNative.FPDF_GetPageSizeByIndex(document, pageIndex, out double pageWidthPt, out double pageHeightPt)) {
+                throw new InvalidOperationException($"Unable to obtain PDF page {pageIndex} size.");
+            }
+
+            IntPtr page = PdfiumNative.FPDF_LoadPage(document, pageIndex);
+            if (page == IntPtr.Zero)
+                throw new InvalidOperationException($"Unable to load PDF page {pageIndex}.");
+
+            try {
+                // PDF coordinates are points (1/72 inch).
+                //
+                // HORZRES/VERTRES are the printable area in
+                // device pixels for the current printer DC.
+                int widthPx = printer.PixelWidth;
+                int heightPx = printer.PixelHeight;
+
+                // Preserve aspect ratio.
+                double scaleX = widthPx / pageWidthPt;
+                double scaleY = heightPx / pageHeightPt;
+                double scale = Math.Min(scaleX, scaleY);
+                int renderWidth = Math.Max(1, (int)Math.Round(pageWidthPt * scale));
+                int renderHeight = Math.Max(1, (int)Math.Round(pageHeightPt * scale));
+                int offsetX = (widthPx - renderWidth) / 2;
+                int offsetY = (heightPx - renderHeight) / 2;
+
+                printer.StartPage();
+                try {
+                    PdfiumNative.FPDF_RenderPage(printer.Hdc, page, offsetX, offsetY, renderWidth, renderHeight, 0, PdfiumNative.FPDF_PRINTING | PdfiumNative.FPDF_ANNOT);
+                } finally {
+                    printer.EndPage();
+                }
+            } finally {
+                PdfiumNative.FPDF_ClosePage(page);
+            }
+        }
+
+        private static string? GetDefaultPrinterName() {
+            using var key = Microsoft.Win32.Registry.CurrentUser.OpenSubKey(@"Software\Microsoft\Windows NT\CurrentVersion\Windows");
+            string? printer = key?.GetValue("Device") as string;
+            if (string.IsNullOrWhiteSpace(printer))
+                return null;
+
+            // Device has the form:
+            // Printer Name,winspool,PORT
+            int comma = printer.IndexOf(',');
+            return comma >= 0 ? printer[..comma] : printer;
+        }
+    }
+}