C#•3y ago

❔ Problem with Dictionary<ulong, Image> (Strange work of memory access)

Concept of my system: A system that draws a picture with stickers, each of the stickers can be moved, there can be an unlimited number of stickers.

Code with explanations in comments:

private static Dictionary<ulong, Image> UserStickerProfiles = new();

public static async Task MoveSticker(Sticker sticker)
{
    var stickerImage = await ItemManager.GetProfileItemImageAsync(itemId); // take image of sticker from file

    UserStickerProfiles.TryGetValue(args.User.Id, out var image);
    if (image == null)
    {
        image = await ProfileMethods.DrawProfileExceptStickerAsync(args.User, itemId); // draw picture without this sticker
        UserStickerProfiles.Add(args.User.Id, image);
    }

    image.Mutate(x => x.DrawImage(stickerImage, new Point(sticker.PositionX, sticker.PositionY), 1f)); // draw this sticker with new coordinations

    // saving and sending
    var memoryStream = new MemoryStream();
    await image.SaveAsPngAsync(memoryStream);
    memoryStream.Seek(0, SeekOrigin.Begin);

    // send image to user with memortStream
}

private static Dictionary<ulong, Image> UserStickerProfiles = new();

public static async Task MoveSticker(Sticker sticker)
{
    var stickerImage = await ItemManager.GetProfileItemImageAsync(itemId); // take image of sticker from file

    UserStickerProfiles.TryGetValue(args.User.Id, out var image);
    if (image == null)
    {
        image = await ProfileMethods.DrawProfileExceptStickerAsync(args.User, itemId); // draw picture without this sticker
        UserStickerProfiles.Add(args.User.Id, image);
    }

    image.Mutate(x => x.DrawImage(stickerImage, new Point(sticker.PositionX, sticker.PositionY), 1f)); // draw this sticker with new coordinations

    // saving and sending
    var memoryStream = new MemoryStream();
    await image.SaveAsPngAsync(memoryStream);
    memoryStream.Seek(0, SeekOrigin.Begin);

    // send image to user with memortStream
}

private static Dictionary<ulong, Image> UserStickerProfiles = new();

public static async Task MoveSticker(Sticker sticker)
{
    var stickerImage = await ItemManager.GetProfileItemImageAsync(itemId); // take image of sticker from file

    UserStickerProfiles.TryGetValue(args.User.Id, out var image);
    if (image == null)
    {
        image = await ProfileMethods.DrawProfileExceptStickerAsync(args.User, itemId); // draw picture without this sticker
        UserStickerProfiles.Add(args.User.Id, image);
    }

    image.Mutate(x => x.DrawImage(stickerImage, new Point(sticker.PositionX, sticker.PositionY), 1f)); // draw this sticker with new coordinations

    // saving and sending
    var memoryStream = new MemoryStream();
    await image.SaveAsPngAsync(memoryStream);
    memoryStream.Seek(0, SeekOrigin.Begin);

    // send image to user with memortStream
}

private static Dictionary<ulong, Image> UserStickerProfiles = new();

public static async Task MoveSticker(Sticker sticker)
{
    var stickerImage = await ItemManager.GetProfileItemImageAsync(itemId); // take image of sticker from file

    UserStickerProfiles.TryGetValue(args.User.Id, out var image);
    if (image == null)
    {
        image = await ProfileMethods.DrawProfileExceptStickerAsync(args.User, itemId); // draw picture without this sticker
        UserStickerProfiles.Add(args.User.Id, image);
    }

    image.Mutate(x => x.DrawImage(stickerImage, new Point(sticker.PositionX, sticker.PositionY), 1f)); // draw this sticker with new coordinations

    // saving and sending
    var memoryStream = new MemoryStream();
    await image.SaveAsPngAsync(memoryStream);
    memoryStream.Seek(0, SeekOrigin.Begin);

    // send image to user with memortStream
}

Problem:
Each time you use this function, a new picture should appear with ALL stickers and the sticker that we moved to a new location. However, it happens that the sticker is duplicated and there are several of them.

The suggestion line

image.Mutate(x => x.DrawImage(stickerImage, new Point(sticker.PositionX, sticker.PositionY), 1f));

image.Mutate(x => x.DrawImage(stickerImage, new Point(sticker.PositionX, sticker.PositionY), 1f));

image.Mutate(x => x.DrawImage(stickerImage, new Point(sticker.PositionX, sticker.PositionY), 1f));

image.Mutate(x => x.DrawImage(stickerImage, new Point(sticker.PositionX, sticker.PositionY), 1f)); updates the Dictionary directly, though it shouldn't be, presumably because C# has a memory bug here.

I am using .NET 7.0

Sherbert Lemon•3/28/23, 8:05 PM

where do itemId and args come from?

Kouhai•3/28/23, 8:08 PM

updates the Dictionary directly, though it shouldn't beupdates the Dictionary directly, though it shouldn't be Do you mean it shouldn't update the instance of image saved in the Dictionary?

Kouhai•3/28/23, 8:09 PM

You're only doing this operation if image == null, so the dictionary isn't effected