Need help in understanding this example code

Question

private void SetAlpha(string location)
{
    //bmp is a bitmap source that I load from an image
    bmp = new BitmapImage(new Uri(location));
    int[] pixels = new int[(int)bmp.Width * (int)bmp.Height];
    //still not sure what 'stride' is.  Got this part from a tutorial
    int stride = (bmp.PixelWidth * bmp.Format.BitsPerPixel + 7)/8;

    bmp.CopyPixels(pixels, stride, 0);
    int oldColor = pixels[0];
    int red = 255;
    int green = 255;
    int blue = 255;
    int alpha = 0;
    int color = (alpha << 24) + (red << 16) + (green << 8) + blue;

    for (int i = 0; i < (int)bmp.Width * (int)bmp.Height; i++)
    {
        if (pixels[i] == oldColor)
        {
            pixels[i] = color;
        }
    }
        //remake the bitmap source with these pixels
        bmp = BitmapSource.Create(bmp.PixelWidth, bmp.PixelHeight, bmp.DpiX, bmp.DpiY, bmp.Format, bmp.Palette, pixels, stride);
    }

}

Could you explain this code for me? What does color and oldColor mean?

Answer 1

This code substitutes and oldColor by a new color in a RGBA bitmap.

The new color is full - copmletely opaque white. The old color is taken from the first pixel. many icons and masks do

Stride is how many bytes per scan line / row there are.

Bugs:

1) bmp.CopyPixels(pixels, stride, 0); only copies the first row. it shouls be bmp.CopyPixels(pixels, stride * bmp.Height, 0);

2) It assusmes a particualr layout of the RGB colors. It allo does not check the results of "new BitmapImage" "new int[]" and BitmapSource.Create

3) the function's name is wrong.