setBlendFunc help.

GregBUG

yes i know it's not documented yet but for my particle engine i really need it...

i need a little help..

for what I understood:

normal blending is:

setBlendFunc(BlendFactor.ZERO, BlendFactor.ZERO)

Additive Alpha Blending

setBlendFunc(BlendFactor.SRC_ALPHA, BlendFactor.ONE)

Solid Alpha Blending

setBlendFunc(BlendFactor.SRC_ALPHA, BlendFactor.ZERO)

but i can't find right combination of
screen alpha blending and multiply alpha blending

(and i don't know if the above are really correct ;;) )
any help?

atilim

Hi Greg,

You can use this (for example add to init.lua):

Sprite.ALPHA = "alpha" Sprite.NO_ALPHA = "noAlpha" Sprite.ADD = "add" Sprite.MULTIPLY = "multiply" Sprite.SCREEN = "screen"   function Sprite:setBlendMode(mode) if type(mode) ~= "string" then error("bad argument #2 to 'setBlendMode' (string expected, got "..type(mode)..")") end   if mode == Sprite.ALPHA then self:setBlendFunc(BlendFactor.SRC_ALPHA, BlendFactor.ONE_MINUS_SRC_ALPHA) elseif mode == Sprite.NO_ALPHA then self:setBlendFunc(BlendFactor.ONE, BlendFactor.ZERO) elseif mode == Sprite.ADD then self:setBlendFunc(BlendFactor.SRC_ALPHA, BlendFactor.ONE) elseif mode == Sprite.MULTIPLY then self:setBlendFunc(BlendFactor.DST_COLOR, BlendFactor.ONE_MINUS_SRC_ALPHA) elseif mode == Sprite.SCREEN then self:setBlendFunc(BlendFactor.ONE, BlendFactor.ONE_MINUS_SRC_COLOR) else error("Parameter 'blendMode' must be one of the accepted values.") end end   Sprite.clearBlendMode = Sprite.clearBlendFunc

After we release the next version, you can safely remove this and continue. Because I've already added this function.

cheers,

GregBUG

thank you very much!

GregBUG

just tested and work fine...
but
screen blending works much like noAlpha :-S

the "screen" blending that i want to do is (like in game*alad particles)
like self:setBlendFunc(BlendFactor.SRC_ALPHA, BlendFactor.ONE_MINUS_DST_ALPHA)
but is not perfect...

@-)

MikeHart

Isn't that the mode Sprite.ALPHA?

GregBUG

no this is a little bit different from ALPHA
alfa is:
(BlendFactor.SRC_ALPHA, BlendFactor.ONE_MINUS_SRC_ALPHA)
what i tried is:
(BlendFactor.SRC_ALPHA, BlendFactor.ONE_MINUS_DST_ALPHA)

SCREEN blending used with an another game engine .. it's a middle way between ALPHA and ADD...
i don't know if IT'S the correct way... but...

atilim

Hi,

I've done some tests at http://www.andersriggelsen.dk/glblendfunc.php

I think the most similar result to screen blend is (BlendFactor.SRC_ALPHA, BlendFactor.ONE_MINUS_SRC_COLOR)

What do you think?

GregBUG

Hi! atilim!

1st. thank for your time on this.

yes the effect are very similar but there are visible black box around the sprites...
if you want i could send to you the sources of particle engine and a litte test program...

atilim

That would be great.
I start to think, there may be no exact way to do screen blending.

GregBUG

email just sent... ;;)

atilim

got it.

atilim

Currently, I cannot see a way to implement screen blending with correct alpha. Maybe the function glBlendFuncSeperate can be a solution but currently I'm not sure if all Android devices support it (e.g. glBlendFuncSeperate is supported for iOS 3.0+). Right now, let's give support for additive and multiplicative blending and leave screen blending for the future releases.

GregBUG

ok. thanks atilim.

add and mul blending may be enough for very many effects!

thanks again for looking at this!. :P

atilim

Hi GregBUG,

With the introduction of premultipled alpha, now the screen blending mode works perfectly. I've added this to the setBlendMode function.

GregBUG

Oh that's fine atilim!!! Thanks.