Question

I’m building a small top down shooter in XNA using C#, and I am trying to implement per-pixel collision detection. I have the following code to do that, along a standard bounding box detection that returns the rectangle containing the collision.

private bool perPixel(Rectangle object1, Color[] dataA, Rectangle object2, Color[] dataB)
    {
        //Bounds of collision
        int top = Math.Max(object1.Top, object2.Top);
        int bottom = Math.Min(object1.Bottom, object2.Bottom);
        int left = Math.Max(object1.Left, object2.Left);
        int right = Math.Min(object1.Right, object2.Right);

        //Check every pixel
        for (int y = top; y < bottom; y++)
        {
            for (int x = left; x < right; x++)
            {
                //Check alpha values
                Color colourA = dataA[(x - object1.Left) + (y - object1.Top) * object1.Width];
                Color colourB = dataB[(x - object2.Left) + (y - object2.Top) * object2.Width];

                if (colourA.A != 0 && colourB.A != 0)
                {
                    return true;
                }
            }
        }
        return false;
    }

I’m pretty sure that that will work, but I am also trying to get some of the objects to check against from a sprite sheet, and I’m trying to use this code to get the colour data, but it is getting an error saying that “The size of the data passed in is too large or small for this resource”.

 Color[] pacmanColour = new Color[frameSize.X * frameSize.Y];

                pacman.GetData(0, new Rectangle(currentFrame.X * frameSize.X, currentFrame.Y * frameSize.Y, frameSize.X, frameSize.Y), pacmanColour,
                    currentFrame.X * currentFrame.Y, (sheetSize.X * sheetSize.Y));

What am I doing wrong?

Answer 1

Let me show you my method for dealing with Texture2D Colors

I used the following technique for loading premade structures from files

//Load the texture from the content pipeline
Texture2D texture = Content.Load<Texture2D>("Your Texture Name and Directory");

//Convert the 1D array, to a 2D array for accessing data easily (Much easier to do Colors[x,y] than Colors[i],because it specifies an easy to read pixel)
Color[,] Colors = TextureTo2DArray(texture);

And the function…

 Color[,] TextureTo2DArray(Texture2D texture)
    {
        Color[] colors1D = new Color[texture.Width * texture.Height]; //The hard to read,1D array
        texture.GetData(colors1D); //Get the colors and add them to the array

        Color[,] colors2D = new Color[texture.Width, texture.Height]; //The new, easy to read 2D array
        for (int x = 0; x < texture.Width; x++) //Convert!
            for (int y = 0; y < texture.Height; y++)
                colors2D[x, y] = colors1D[x + y * texture.Width];

        return colors2D; //Done!
    }

It will return a simple to use 2D array of colors, So you can simply check if Colors[1,1] (For pixel 1,1) equals whatever.