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我正在编写一个显示地图的程序，并在其顶部显示相机位置及其观察方向的另一层。地图本身可以缩放和平移。问题是地图文件很大，缩放不顺畅。

我创建class ZoomablePictureBox : PictureBox以添加缩放和平移功能。我尝试了不同的方法，来自这个论坛和其他论坛，用于缩放和平移，最终得到以下结果，触发以下OnPaint事件ZoomablePictureBox：

  private void DrawImgZoomed(PaintEventArgs e)
    {
        e.Graphics.SmoothingMode = SmoothingMode.AntiAlias;

            if (imgZoomed != null)
                e.Graphics.DrawImage(imgZoomed, new Rectangle(-ShiftX, -ShiftY, imgZoomed.Width, imgZoomed.Height), 0, 0, imgZoomed.Width, imgZoomed.Height, GraphicsUnit.Pixel);

    }

其中 ShiftX 和 ShiftY 提供正确的地图平移（与此问题无关的计算）。

imgZoomed是每次缩放更改时在 BackgroundWorker 中计算的原始地图的缩放版本：

private void bgWorker_DoWork(object sender, DoWorkEventArgs e)
    {

        Bitmap workerImage = e.Argument as Bitmap;
        Bitmap result;

        result = new Bitmap(workerImage, new Size((int)(workerImage.Width * Zoom), (int)(workerImage.Height * Zoom)));

        e.Result = result;
    }

所以目前的做法是，每次用户滚动鼠标滚轮时，imgZoomed都会根据当前缩放计算新的。地图大小约为 30 MB，这可能需要 0.5 秒，这很烦人，但平移运行平稳。

我意识到这可能不是最好的主意。在以前的方法中，我没有在每次滚动鼠标时创建缩放图像副本，而是这样做：

e.Graphics.DrawImage(Image, new Rectangle(-ShiftX, -ShiftY, (int)(this._image.Width * Zoom), (int)(this._image.Height * Zoom)), 0, 0, Image.Width, Image.Height, GraphicsUnit.Pixel);

缩放更平滑，因为据我了解，它只是拉伸了原始图像。另一方面，平移正在大量跳过。

我在想：

  • 为每次放大内存/硬盘驱动器创建原始地图的副本 - 它会占用太多内存/硬盘空间
  • 为下一个/实际/上一个缩放创建原始地图的副本，这样我就有更多时间来计算下一步 - 如果用户一次滚动不止一个步骤，这将无济于事

我还尝试了矩阵变换 - 没有真正的性能提升，计算 pan 真的很痛苦。

我在这里兜圈子，不知道该怎么做。如果我在默认的 Windows 图片查看器中打开地图，则缩放和平移很流畅。他们是怎么做到的？

如何同时实现平滑的缩放和平移？

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1 回答 1

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Sorry this is so long, I left in only the essential parts.

Most of the p/invoke stuff is taken from pinvoke.net

My solution for smooth panning across large images involves using the StretchBlt gdi method instead of Graphics.DrawImage. I've created a static class that groups all the native blitting operations.

Another thing that helps greatly is caching the HBitmap and Graphics objects of the Bitmap. 

public class ZoomPanWindow
{
    private Bitmap map;
    private Graphics bmpGfx;
    private IntPtr hBitmap;

    public Bitmap Map
    {
        get { return map; }
        set 
        {
            if (map != value)
            {
                map = value;
                //dispose/delete any previous caches
                if (bmpGfx != null) bmpGfx.Dispose();
                if (hBitmap != null) StretchBltHelper.DeleteObject(hBitmap);
                if (value == null) return;
                //cache the new HBitmap and Graphics.
                bmpGfx = Graphics.FromImage(map);
                hBitmap = map.GetHbitmap();
             }
        }
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        if (map == null) return;
        //finally, the actual painting!
        Rectangle mapRect = //whatever zoom/pan logic you implemented.
        Rectangle thisRect = new Rectangle(0, 0, this.Width, this.Height);
        StretchBltHelper.DrawStretch(
            hBitmap,
            bmpGfx,
            e.Graphics,
            mapRect,
            thisRect);
    }
}

public static class StretchBltHelper
{
    public static void DrawStretch(IntPtr hBitmap, Graphics srcGfx, Graphics destGfx,
        Rectangle srcRect, Rectangle destRect)
    {
        IntPtr pTarget = destGfx.GetHdc();
        IntPtr pSource = CreateCompatibleDC(pTarget);
        IntPtr pOrig = SelectObject(pSource, hBitmap);
        if (!StretchBlt(pTarget, destRect.X, destRect.Y, destRect.Width, destRect.Height,
            pSource, srcRect.X, srcRect.Y, srcRect.Width, srcRect.Height,
            TernaryRasterOperations.SRCCOPY))
        throw new Win32Exception(Marshal.GetLastWin32Error());

        IntPtr pNew = SelectObject(pSource, pOrig);
        DeleteDC(pSource);
        destGfx.ReleaseHdc(pTarget);
    }

    [DllImport("gdi32.dll", EntryPoint = "SelectObject")]
    public static extern System.IntPtr SelectObject(
        [In()] System.IntPtr hdc,
        [In()] System.IntPtr h);

    [DllImport("gdi32.dll", ExactSpelling = true, SetLastError = true)]
    static extern bool DeleteDC(IntPtr hdc);

    [DllImport("gdi32.dll", EntryPoint = "DeleteObject")]
    [return: MarshalAs(UnmanagedType.Bool)]
    public static extern bool DeleteObject(
        [In()] System.IntPtr ho);

    [DllImport("gdi32.dll", ExactSpelling = true, SetLastError = true)]
    static extern IntPtr CreateCompatibleDC(IntPtr hdc);

    [DllImport("gdi32.dll")]
    static extern bool StretchBlt(IntPtr hdcDest, int nXOriginDest, int nYOriginDest,
        int nWidthDest, int nHeightDest,
        IntPtr hdcSrc, int nXOriginSrc, int nYOriginSrc, int nWidthSrc, int nHeightSrc,
        TernaryRasterOperations dwRop);

    public enum TernaryRasterOperations : uint
    {
        SRCCOPY = 0x00CC0020
        //there are many others but we don't need them for this purpose, omitted for brevity
    }
}
于 2012-11-29T11:06:09.443 回答