Analysis of information sources in references of the Wikipedia article "Alpha compositing" in English language version.
By switching to pre-multiplied blend mode for all particle effects, and entire scene can be done with one draw call (assuming atlasing/2D array for the textures)... Another neat trick with pre-multiplied alpha is that if you have overlapping textures that are in known positions, you can pre-process them all down to one texture.
Win2D uses straight alpha in its API surface, but premultiplied alpha for internal rendering operations.
However, something interesting happens when we generate the next mipmap level...
