What are "alpha effects" ?

[futurefields]

Some random quotes:

"Neither one of the levels on show is especially worse than the other in this regard, and it's clearly the barrage of alpha effects that ends up pressing the hardware too far."

"Alas, there are still familiar weak points; drops to 15FPS are commonplace during sequences filled with transparent alpha effects."

"It isn't a pretty sight on either console once alpha effects are involved, and it's disappointing to see such glaring issues cropping up in a game released at the tail end of the generation."

"A big effort was made there; though performance remained slightly behind on PS3 where transparent alpha filled the screen, the extra time investment paid off in a very handsome port indeed."

"Alpha effects, iron sights and sniper scope effects now seem to incur a significant performance penalty on Call of Duty: Ghosts - something that didn't seem to be an issue when we previously tested the game."

Seem to be performance killers.

 

[KaOTiK]

opacity/transparency

 

[Exophase]

It comes from alpha blending, which is (alpha * new_pixel) + ((1 - alpha) * pixel_underneath). Here alpha determines how translucent the pixel is, where the closer alpha is to 0 the more the pixel that was already there (the thing beneath the material that's being rendered) shows through, and the closer it is to 1 the more the new pixel (material being rendered) shows through.

These days people use alpha effects to mean any effect where the old pixel at the current location is read (from the framebuffer) and some calculation is done to combine it with the new pixel. These effects are usually done by at least partially by the ROP units. It can have a big impact on performance because of the additional framebuffer requirements, but also because of how it interferes with deferred rendering and has to be handled with special techniques.

 

[BrightCandle]

You could also argue the grand majority of pixel shader programs are infact alpha effects because a lot of it is adding lighting, explosions etc over the top of the rendered image to a varying amount.

Alpha is just a transparency value and its used much like red, green and blue in many places in the graphics pipeline but I doubt they mean transparent windows. I think they mean post processing effects like radial blur (iron sight effect), motion blur and partially transparent effects like explosions, debris and smoke.

 

[Todd33]

Used for things like fire, explosions, sparks, fences, etc. Textures that show part of the background.