How to draw transparent polygons?

This is for Pillow, a more maintained fork of PIL. http://pillow.readthedocs.org/

If you want to draw polygons that are transparent, relative to each other, the base Image has to be of type RGB, not RGBA, and the ImageDraw has to be of type RGBA. Example:

from PIL import Image, ImageDraw

img = Image.new('RGB', (100, 100))
drw = ImageDraw.Draw(img, 'RGBA')
drw.polygon(xy=[(50, 0), (100, 100), (0, 100)], fill=(255, 0, 0, 125))
drw.polygon(xy=[(50, 100), (100, 0), (0, 0)], fill=(0, 255, 0, 125))
del drw

img.save('out.png', 'PNG')

This will draw two triangles overlapping with their two colors blending. This a lot faster than having to composite multiple ‘layers’ for each polygon.