从两点中裁剪图像（C＃）

Question

Update:

Updated code added.

However for some reason it still doesn't work properly. If the coordinates are Bitmap coordinates, what could be the reason? The first code sample I put here doesn't work properly and the second gives me an OutOfMemoryException.

I've ran into a problem trying to crop an image between two points. In my project I have a pictureBox (named AP), and the general idea is that the user clicks on two points and the program crops the image between these two corners. I've tried two methods, one with Bitmap.Crop and the other one with Graphics.DrawImage, but both seemed to fail for the same reason and didn't work at all (cropped a much smaller portion of the image).

Code:

    private void AP_Click(object sender, EventArgs e)
    {
        // Setting the corners
        else if (mark_shape == 0)
        {
            var mouseEventArgs = e as MouseEventArgs;
            if (picture_corners_set == 0)
            {
                northEast = AP.PointToClient(new Point(mouseEventArgs.X, mouseEventArgs.Y));
                picture_corners_set = 1;
            }
            else if (picture_corners_set == 1)
            {
                southWest = AP.PointToClient(new Point(mouseEventArgs.X, mouseEventArgs.Y));
                Rectangle imageRectangle = new Rectangle(southWest.X, northEast.Y, (northEast.X - southWest.X), (southWest.Y - northEast.Y));
                var bmp = new Bitmap(imageRectangle.Width, imageRectangle.Height);
                using (var gr = Graphics.FromImage(bmp))
                {
                    gr.DrawImage(AP.Image, 0, 0, imageRectangle, GraphicsUnit.Pixel);
                }
                AP.Image = bmp;
                enableAllButtons();
            }
        }
    }

Answer 1

Since your cropped Bitmap image size is the same as the width/height of the user selection, I'm guessing you want that cropped image to be in the top/left of the new Bitmap and fill it. As it is, you're telling the DrawImage() method to draw that portion of the Bitmap in the same location, albeit in a smaller size Bitmap.

The correct way to do this is to draw the source rectangle image at (0, 0):

    private Point pt1, pt2;

    private void AP_Click(object sender, EventArgs e)
    {

        // ... obviously other code here ...            

        else if (mark_shape == 0) // Setting the corners
        {
            Point pt = AP.PointToClient(Cursor.Position);
            if (picture_corners_set == 0)
            {
                pt1 = new Point(pt.X, pt.Y);
                picture_corners_set = 1;
            }
            else if (picture_corners_set == 1)
            {
                pt2 = new Point(pt.X, pt.Y);
                picture_corners_set = 0;

                Rectangle imageRectangle = new Rectangle(new Point(Math.Min(pt1.X, pt2.X), Math.Min(pt1.Y, pt2.Y)), new Size(Math.Abs(pt2.X - pt1.X) + 1, Math.Abs(pt2.Y - pt1.Y) + 1));
                var bmp = new Bitmap(imageRectangle.Width, imageRectangle.Height);
                using (var gr = Graphics.FromImage(bmp))
                {
                    gr.DrawImage(AP.Image, 0, 0, imageRectangle, GraphicsUnit.Pixel);
                }
                AP.Image = bmp;
                enableAllButtons();
            }
        }
    }

There are several other overloads you could use to do this, but the one above makes it pretty clear that imageRectangle is being drawn at (0, 0).