Bitmap Graphics vs WinForm Control Graphics

Question

I'm just using a .NET port of Pdfium named PdfiumViewer. It just works very well once rendered in the WinForm controls but when I try to render it on a Bitmap to show in the WPF windows (or even saving to disk) the rendered text has problem.

var pdfDoc = PdfiumViewer.PdfDocument.Load(FileName);
int width = (int)(this.ActualWidth - 30) / 2;
int height = (int)this.ActualHeight - 30;            

var bitmap = new System.Drawing.Bitmap(width, height);

var g = System.Drawing.Graphics.FromImage(bitmap);

g.FillRegion(System.Drawing.Brushes.White, new System.Drawing.Region(
    new System.Drawing.RectangleF(0, 0, width, height)));

pdfDoc.Render(1, g, g.DpiX, g.DpiY, new System.Drawing.Rectangle(0, 0, width, height), false);

// Neither of these are readable
image.Source = BitmapHelper.ToBitmapSource(bitmap);
bitmap.Save("test.bmp");

// Directly rendering to a System.Windows.Forms.Panel control works well
var controlGraphics = panel.CreateGraphics(); 
pdfDoc.Render(1, controlGraphics, controlGraphics.DpiX, controlGraphics.DpiY,
    new System.Drawing.Rectangle(0, 0, width, height), false);

It's notable to say that I tested almost every possible options on the Graphics object including TextContrast,TextRenderingHint,SmoothingMode,PixelOffsetMode, ...

Which configurations I'm missing on the Bitmap object that cause this?

Edit 2

After lots of searching and as @BoeseB mentioned I just found that Pdfium render device handle and bitmaps differently by providing a second render method FPDF_RenderPageBitmap and currently I'm struggling to convert its native BGRA bitmap format to managed Bitmap.

Edit

Different modes of TextRenderingHint

Also tried Application.SetCompatibleTextRenderingDefault(false) with no noticeable difference.

Answer 1

Isn't it your issue ? Look recent fix for it. As you can see, repository owner commited newer version of PdfiumViewer. Now you can write this way:

var pdfDoc = PdfDocument.Load(@"mydoc.pdf");
var pageImage = pdfDoc.Render(pageNum, width, height, dpiX, dpiY, isForPrinting);
pageImage.Save("test.png", ImageFormat.Png);

// to display it on WPF canvas
BitmapSource source = ImageToBitmapSource(pageImage);
canvas.DrawImage(source, rect);     // canvas is instance of DrawingContext

Here is a popular approach to convert Image to ImageSource

BitmapSource ImageToBitmapSource(System.Drawing.Image image)
{
    using(MemoryStream memory = new MemoryStream())
    {
        image.Save(memory, ImageFormat.Bmp);
        memory.Position = 0;
        var source = new BitmapImage();
        source.BeginInit();
        source.StreamSource = memory;
        source.CacheOption = BitmapCacheOption.OnLoad;
        source.EndInit();

        return source;
    }
}