What do the blend modes in pygame mean?

Question

Surface.blit has a new parameter in 1.8: blend. The following values are defined:

• BLEND_ADD
• BLEND_SUB
• BLEND_M

Answer 1

Those are blending modes for compositing images on top of each other. The name of the blending mode already tells you the underlying operation.

The BLEND_* constants are simply aliases for the BLEND_RGB_* constants and the BLEND_RGBA_* variants operate on all four channels (including the alpha channel) as opposed to only RGB.

For general information about the different blending modes and their respective effects, see here.