CODEWITHSUNDEEP
c#wpf
shady
shady

Reputation: 1106

wpf create transparent writeablebitmap

When I create one like this: 

WriteableBitmap wb = new WriteableBitmap(1200, 1600, 90, 90, PixelFormats.Bgr24, null);

Its filled with black when I want it to be transparent. I tried Clear(from WriteableBitmapEx library) but I get a Attempted to read or write protected memory. This is often an indication that other memory is corrupt."} System.Exception {System.AccessViolationException}

wb.Clear(Colors.Transparent);

Any ideas how I could accomplish this?

Edit:

        List<FormattedText> text = new List<FormattedText>();
        WriteableBitmap wb = new WriteableBitmap(1200, 1600, 96, 96, PixelFormats.Bgr32, null);
        wb.Clear(Colors.Transparent);

        TransformedBitmap tb = new TransformedBitmap(wb, new RotateTransform(0));
        DrawingVisual drawingVisual = new DrawingVisual();
        DrawingContext drawingContext = drawingVisual.RenderOpen();
        drawingContext.DrawImage(tb, new Rect(0, 0, tb.PixelWidth, tb.PixelHeight));



        for (int i = 0; i < text.Count; i++)
        {

            drawingContext.DrawText(text[i], points[i]);
            drawingContext.DrawEllipse(null, new Pen(new SolidColorBrush(Colors.Aqua), 3), points[i], 10, 10);
        }

        drawingContext.Close();

        System.Windows.Media.Imaging.RenderTargetBitmap bmp = new System.Windows.Media.Imaging.RenderTargetBitmap(tb.PixelWidth, tb.PixelHeight, 96, 96, PixelFormats.Pbgra32);
        bmp.Render(drawingVisual);

        Image = bmp;

Upvotes: 1

Views: 3032

Answers (1)

Clemens
Clemens

Reputation: 128013

Create the WriteableBitmap with a PixelFormat that has an alpha channel and thus allows for transparency, e.g. PixelFormats.Bgra32:

var wb = new WriteableBitmap(1200, 1600, 96, 96, PixelFormats.Bgra32, null);

Now you have four bytes per pixel, one for blue, one for green, one for red, and one for the alpha value.

Note also that you would usually use a value of 96 for the DPI parameters.

Upvotes: 2

Related Questions