Image Manipulation Class - Watermark position

[eluser]Ficoder[/eluser]
Hi,
I use image_lib in my current site, but there is one thing that i want to change. I'm using this lib to add texts to images with 100opacity, but there is problem cause library is positioning watermark to bottom by default. So i play with the wm_hor_offset and wm_vrt_offset. If i set both to 0 (zero), then text is again at the bottom, so it's vertical offset is working invert by design.

I want to change that, when bot is set to 0 (zero), then text is at the top left position. What is easiest way to achieve that?