Photobomb has lacked the ability to set the opacity of images the way it could set the opacity of text and scribbles. This was because goocanvas.Image lacked this capability, and I could not figure out how to make a pixbuf transparent. I looked through all the pygtk docs, all the PIL docs, and all the cairo docs. I tried a bunch of things, and just couldn't make it happen.
I finally ended up with a solution that works (but is a tad slow on larger images). To start, you need a transparent PNG file loaded into a pixbuf. I do this by storing a transparent PNG image on disk. If I was slicker, I could probably create one out of thin air using the various pixbuf functionalities. You also need a pixbuf that you want to make transparent.
Anyway, given a transparent pixbuf, this function will set the transparency.
def change_opacity(self, opacity):
change_opacity - changes the opacity of pixbuf by combining
the pixbuf with a pixbuf derived from a transparent .png
opacity - the degree of desired opacity (between 0 and 255)
returns: a pixbuf with the transperancy
trans = self.transparent_img
width = self.pixbuf.get_width()
height = self.pixbuf.get_height()
trans = trans.scale_simple(width,height,gtk.gdk.INTERP_NEAREST)
self.pixbuf.composite(trans, 0, 0, width, height, 0, 0, 1, 1, gtk.gdk.INTERP_NEAREST, opacity)
I'm sharing it here in case someone else runs into this and can either use my solution, or offer a better one.