Question

I’m trying to implement a function that takes a System.Drawing.Bitmap object and renders it on a WPF Canvas. The bitmap has to be cropped and joined a few times before rendering.

Environment: WPF application running on .NET 3.5 SP1

Input: System.Drawing.Bitmap object, of size 800×600 and pixel format RGB24

Goal: to display an image which is composed of two stripes of the input bitmap (on one line). The stripes are two bitmap halves – (0,0,800,300) and (0,300,800,600). Later on I want to be able to scale the image up or down.

I’ve already implemented a solution with GDI and Graphics.DrawImage (that renders into a Bitmap object), but I want to improve performance (this function could be called 30 times per second).

Is there a faster way to implement this with WPF, assuming I want to render the image on a WPF window?

Answer 1

The best solution I found so far is using WriteableBitmap, something like this:

void Init()
{
    m_writeableBitmap = new WriteableBitmap(DesiredWidth, DesiredHeight, DesiredDpi, DesiredDpi, PixelFormats.Pbgra32, null);
{

void CopyPixels(System.Drawing.Bitmap frame, Rectangle source, Point destBegin)
{
    var bmpData = frame.LockBits(source, ImageLockMode.ReadOnly, frame.PixelFormat);
    m_writeableBitmap.Lock();

    var dest = new Int32Rect(destBegin.X, destBegin.Y, bmpData.Width, bmpData.Height);
    m_writeableBitmap.WritePixels(dest, bmpData.Scan0, bmpData.Stride * bmpData.Height, bmpData.Stride);

    m_writeableBitmap.Unlock();
    frame.UnlockBits(bmpData);
}

CopyPixels would be called twice for the use case I described in my question (two stripes).