Bit blit Bitmaps (WriteableBitmapEx Framework)

Question

I've not fully understand the basics of Bit blit bitmaps.

I'm using the WriteableBitmapEx framework (WPF). My bitmap represents a map and what I wanna achieve is to copy a (moving) symbol into that map.

For actual copying, I use the function Blit:

  _bitmap.Blit(myObject.Value.Location.ToWindowsPoint(), symbol, rect, Colors.Cyan,
                         WriteableBitmapExtensions.BlendMode.Additive);

where symbol is a png image(transparent background).

This works in prinicpal but I do not understand how the color (Colors.Cyan) is applied by the blend mode. I've tried out all available blend modes but I've not succeeded in getting Cyan as the color of the symbol or I got the color but then the transparent background was also copied to the source bitmap (black background).

Is 'Bliting' the wrong approach for my use case?

Thanks.

Answer 1

A much easier approach is to use images (corresponding WPF ui element) and layer it above the bitmap. This has also the advantage that you can move the image without redrawing the bitmap at all.