在C＃中旋转图像时如何防止剪裁？ [英] How do I prevent clipping when rotating an image in C#?

问题描述

我刚刚经历了一些尝试弄清楚如何让图像旋转的东西。这有效，但现在它正在削减，我不确定如何让它停止...我正在使用这个rotateImage方法：

I just went through a bunch of stuff trying to figure out how to get the image to even rotate. That works but now it's clipping and I'm not really sure how to make it stop... I'm using this rotateImage method:

public static Image RotateImage(Image img, float rotationAngle)
    {
        //create an empty Bitmap image
        Bitmap bmp = new Bitmap(img.Width, img.Height);

        //turn the Bitmap into a Graphics object
        Graphics gfx = Graphics.FromImage(bmp);

        //now we set the rotation point to the center of our image
        gfx.TranslateTransform((float)bmp.Width / 2, (float)bmp.Height / 2);

        //now rotate the image
        gfx.RotateTransform(rotationAngle);

        gfx.TranslateTransform(-(float)bmp.Width / 2, -(float)bmp.Height / 2);

        //set the InterpolationMode to HighQualityBicubic so to ensure a high
        //quality image once it is transformed to the specified size
        gfx.InterpolationMode = InterpolationMode.HighQualityBicubic;

        //now draw our new image onto the graphics object
        gfx.DrawImage(img, new System.Drawing.Point(0, 0));

        //dispose of our Graphics object
        gfx.Dispose();

        //return the image
        return bmp;
    }

我尝试将空位图放大，但仅适用于一侧，因为图像固定在位图的左上角。任何想法都将不胜感激！

I tried making the empty bitmap larger but that only works for one side since the image is pinned to the upper left corner of the bitmap. Any ideas would be appreciated!

推荐答案

我从其他网站找到了一些帮助。以下是我最终要为那些想知道的人做的事情：

I found some help from another website. Here's what I ended up doing for those of you who want to know:

// Rotates the input image by theta degrees around center.
    public static Bitmap RotateImage(Bitmap bmpSrc, float theta)
    {
        Matrix mRotate = new Matrix();
        mRotate.Translate(bmpSrc.Width / -2, bmpSrc.Height / -2, MatrixOrder.Append);
        mRotate.RotateAt(theta, new System.Drawing.Point(0, 0), MatrixOrder.Append);
        using (GraphicsPath gp = new GraphicsPath())
        {  // transform image points by rotation matrix
            gp.AddPolygon(new System.Drawing.Point[] { new System.Drawing.Point(0, 0), new System.Drawing.Point(bmpSrc.Width, 0), new System.Drawing.Point(0, bmpSrc.Height) });
            gp.Transform(mRotate);
            System.Drawing.PointF[] pts = gp.PathPoints;

            // create destination bitmap sized to contain rotated source image
            Rectangle bbox = boundingBox(bmpSrc, mRotate);
            Bitmap bmpDest = new Bitmap(bbox.Width, bbox.Height);

            using (Graphics gDest = Graphics.FromImage(bmpDest))
            {  // draw source into dest
                Matrix mDest = new Matrix();
                mDest.Translate(bmpDest.Width / 2, bmpDest.Height / 2, MatrixOrder.Append);
                gDest.Transform = mDest;
                gDest.DrawImage(bmpSrc, pts);
                return bmpDest;
            }
        }
    }

    private static Rectangle boundingBox(Image img, Matrix matrix)
    {
        GraphicsUnit gu = new GraphicsUnit();
        Rectangle rImg = Rectangle.Round(img.GetBounds(ref gu));

        // Transform the four points of the image, to get the resized bounding box.
        System.Drawing.Point topLeft = new System.Drawing.Point(rImg.Left, rImg.Top);
        System.Drawing.Point topRight = new System.Drawing.Point(rImg.Right, rImg.Top);
        System.Drawing.Point bottomRight = new System.Drawing.Point(rImg.Right, rImg.Bottom);
        System.Drawing.Point bottomLeft = new System.Drawing.Point(rImg.Left, rImg.Bottom);
        System.Drawing.Point[] points = new System.Drawing.Point[] { topLeft, topRight, bottomRight, bottomLeft };
        GraphicsPath gp = new GraphicsPath(points,
                                                            new byte[] { (byte)PathPointType.Start, (byte)PathPointType.Line, (byte)PathPointType.Line, (byte)PathPointType.Line });
        gp.Transform(matrix);
        return Rectangle.Round(gp.GetBounds());
    }

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