Thread: Fast way to blit between bitmaps

Anyone know of a fast way to take a smaller bitmap from a larger bitmap?

Bitmap.Clone() runs out of memory after 30 images. I need to create hundreds of tiles from a larger image.

All the examples I've found use LockBits which requires some unmanaged pointers. Not that I don't like pointers but dealing with them in C# does not look fun and the Marshal class appears to only copy much like memcpy does. So it's not possible to specify a rectangle nor control the areas it copies unless I copy one scan line at a time.

Well since no one seems to have a better solution yet I'm going to code a C++ module that uses inline assembly to do the copying and then create an ATL COM DLL so I can use it easily in C#.

Maybe something like this Bubba.
http://msdn2.microsoft.com/en-us/lib...fromimage.aspx

Nah that creates a graphics object from an image. I'm using that to create a graphics object from my bitmap which represents the screen. Similar to creating a memory DC and then blitting from that to the client DC.

I've nearly completed the assembly code but I'm so rusty at it. My main problem is when doing a rep movsd if the length in ecx is not evenly divisible by 4 (the size of a DWORD) then some bytes are left.

I think a simple and operation followed by a rep movsb ought to do the trick to get the remaning bytes.

So something like this wouldn't work for you Bubba

Code:

protected override void OnPaint(PaintEventArgs e)
{
    base.OnPaint(e);

    //Load a bitmap and create a new one to draw a sub bitmap
    Bitmap greenRed = (Bitmap)Bitmap.FromFile("greenred.bmp");
    Bitmap destImage = new Bitmap(20, greenRed.Height);

    //Grab the drawing surface for the new image
    Graphics destGraphics = Graphics.FromImage(destImage);

    //Draw the old one into the new ones smaller space
    destGraphics.DrawImage(greenRed, 0, 0);

    //Draw both on the screen
    e.Graphics.DrawImage(greenRed, new Point(0, 0));
    e.Graphics.DrawImage(destImage, new Point(100,0));
}