c# - lockbits 是否需要固定？

Question

我有一些代码有错误“AccessViolationException 未被用户代码处理:试图读取或写入 protected 内存...”

违规函数的精简版如下:

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]);

甚至替换为:

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？我认为 LockBits 应该这样做...

如果这还不够回答，这里还有一些我试过的:我添加了行

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

如果 fastBackground Canvas 或尺寸被其他函数修改，则退出 OnPaint。

我可以使用互斥锁来防止修改位图fastBackground 和Canvas 的函数与paint (正如我认为的那样)，但我宁愿以另一种方式阻止它们，因为 Canvas 是公开的，我不想要求将互斥体传递到类之外。

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。 (程序员太笨了)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);
                            }
                        }

Answer 1

将我的评论移到答案中，因为它有助于解决问题:

LockBits 返回的缓冲区不需要 Fixed，因为它是非托管内存。你的指针算法是错误的。找到错误。创建一个简单的重现来帮助找到错误。