是固定的，需要使用锁定位

我有一些代码出现错误"用户代码未处理AccessViolationException：试图读取或写入受保护的内存…"

违规功能的精简版本如下：

protected override void OnPaint(PaintEventArgs pe)
{
    if ((updatingFastBackground) || (Calculating)) return; //ADDED FOR DEBUGGING, SEE BELOW
            BitmapData canvasData = Canvas.LockBits(new Rectangle(Point.Empty, Canvas.Size), ImageLockMode.WriteOnly, FastPixelFormat);
            BitmapData fbgData = fastBackground.LockBits(new Rectangle(Point.Empty, fastBackground.Size), ImageLockMode.ReadOnly, FastPixelFormat);
            try
            {
                unsafe
                {
                    byte* canvasDataScan0 = (byte*)canvasData.Scan0.ToPointer();
                    byte* fbgDataScan0 = (byte*)fbgData.Scan0.ToPointer();
                    Rectangle spriteBounds = new Rectangle(Point.Empty, ButtonImages.ImageSize);
                    for (int i = 0; i < ButtonImages.Images.Count; i++)
                    {
                        // Button offset location
                        Point l = new Point(
                            (int)((i % columnCount) * hStep + myIVM.Location.X),
                            (int)((i / columnCount) * vStep + myIVM.Location.Y));
                        // Paint at current location?
                        if (buttonPaintBounds.Contains(l))
                        {
                            BitmapData spriteData = buttonBitmaps[i].LockBits(spriteBounds, ImageLockMode.ReadOnly, FastPixelFormat);
                            try
                            {
                                int spriteLeft = Math.Max(l.X, 0);
                                int spriteRight = Math.Min(l.X + ButtonImages.ImageSize.Width, canvasData.Width);
                                int spriteTop = Math.Max(l.Y, 0);
                                int spriteBottom = Math.Min(l.Y + ButtonImages.ImageSize.Height, canvasData.Height);
                                int spriteWidth = spriteRight - spriteLeft;
                                int spriteHeight = spriteBottom - spriteTop;
                                byte* canvasRowLeft = canvasDataScan0 + (spriteTop * canvasData.Stride) + spriteLeft * 4;
                                byte* spriteRowLeft =
                                    (byte*)spriteData.Scan0.ToPointer() +
                                    Math.Max((spriteTop - l.Y), 0) * spriteData.Stride +
                                    Math.Max((spriteLeft - l.X), 0) * 4;
                                for (int y = 0; y < spriteHeight; y++)
                                {
                                    canvasRowLeft += canvasData.Stride;
                                    spriteRowLeft += spriteData.Stride;
                                    Byte* canvasWalk = (Byte*)canvasRowLeft;
                                    Byte* spriteWalk = (Byte*)spriteRowLeft;
                                    for (int x = 0; x < spriteWidth; x++)
                                    {
                                        if (spriteWalk[3] != 255)
                                        {
                                            canvasWalk[0] = (byte)(canvasWalk[0] * spriteWalk[3] / 255 + spriteWalk[0]);
                                            canvasWalk[1] = (byte)(canvasWalk[1] * spriteWalk[3] / 255 + spriteWalk[1]);
                                            canvasWalk[2] = (byte)(canvasWalk[2] * spriteWalk[3] / 255 + spriteWalk[2]);
                                        }
                                        canvasWalk += 4;
                                        spriteWalk += 4;
                                    }
                                }
                                thesePoints.Add(l);
                            }
                            finally
                            {
                                buttonBitmaps[i].UnlockBits(spriteData);
                            }
                        }

错误发生在线路上：

canvasWalk[0] = (byte)(canvasWalk[0] * spriteWalk[3] / 255 + spriteWalk[0]);

甚至在替换为时

canvasWalk[0] = 0;

迭代变量y和x每次崩溃时都有不同的值，所以这让我相信外部函数正在修改Canvas位图。

如果这实际上是我的问题，有没有办法防止fastBackground和Canvas被外部修改？我以为LockBits应该这么做。。。

如果这还不足以回答问题，下面是我尝试过的更多内容：我添加了行

if ((updatingFastBackground) || (Calculating)) return;

如果fastBackground Canvas或维度正在被其他函数修改，则退出OnPaint。

我可以使用互斥来阻止修改位图fastBackground和Canvas的函数在绘制的同时运行（我认为它们必须是），但我宁愿用另一种方式来阻止它们，因为Canvas是公共的，我不想要求从类中传递互斥。

根据@usr的建议，这个进一步精简的版本不会失败。。。一定是PTD错误。（程序员太笨）即算术错误

protected override void OnPaint(PaintEventArgs pe)
{
    if ((updatingFastBackground) || (Calculating)) return; //ADDED FOR DEBUGGING, SEE BELOW
            BitmapData canvasData = Canvas.LockBits(new Rectangle(Point.Empty, Canvas.Size), ImageLockMode.WriteOnly, FastPixelFormat);
            BitmapData fbgData = fastBackground.LockBits(new Rectangle(Point.Empty, fastBackground.Size), ImageLockMode.ReadOnly, FastPixelFormat);
            try
            {
                unsafe
                {
                    byte* canvasDataScan0 = (byte*)canvasData.Scan0.ToPointer();
                    byte* fbgDataScan0 = (byte*)fbgData.Scan0.ToPointer();
                    Rectangle spriteBounds = new Rectangle(Point.Empty, ButtonImages.ImageSize);
                    for (int i = 0; i < ButtonImages.Images.Count; i++)
                    {
                        // Button offset location
                        Point l = new Point(
                            (int)((i % columnCount) * hStep + myIVM.Location.X),
                            (int)((i / columnCount) * vStep + myIVM.Location.Y));
                        // Paint at current location?
                        if (buttonPaintBounds.Contains(l))
                        {
                            BitmapData spriteData = buttonBitmaps[i].LockBits(spriteBounds, ImageLockMode.ReadOnly, FastPixelFormat);
                            try
                            {
                                byte* canvasRowLeft = canvasDataScan0;
                                byte* spriteRowLeft = (byte*)spriteData.Scan0.ToPointer();
                                for (int y = 0; y < 145; y++)
                                {
                                    canvasRowLeft += canvasData.Stride;
                                    spriteRowLeft += spriteData.Stride;
                                    Byte* canvasWalk = (Byte*)canvasRowLeft;
                                    Byte* spriteWalk = (Byte*)spriteRowLeft;
                                    for (int x = 0; x < 145; x++)
                                    {
                                        if (spriteWalk[3] != 255)
                                        {
                                            canvasWalk[0] = 0;
                                            canvasWalk[1] = 0;
                                            canvasWalk[2] = 0;
                                        }
                                        canvasWalk += 4;
                                        spriteWalk += 4;
                                    }
                                }
                                thesePoints.Add(l);
                            }
                            finally
                            {
                                buttonBitmaps[i].UnlockBits(spriteData);
                            }
                        }