[PD] gem motion blur & alpha

[andre rc]

Thank you for the patch Cyrille. It's a very nice solution.
The only disadvantage is that it makes the background image feedback
dependent.
My goal is to isolate the feedback from other geos & image/videos.
So, I was thinking that in order to keep the blur I have to keep the
gemframebuffer RGB format and add transparency after it.
I just realized that [alpha] has several blending functions, some of them
turn the whole framebuffer transparent.
This is fine but now the geo and blur are also affected (see attached).
I don't know if it is possible to add other type of blending after the
framebuffer, maybe sending it to another gemframebuffer and changing the
background color (black) to alpha?
I saw that pix_alpha achieve this but I don't know how to use it only with
the framebuffer image. Any suggestion is welcomed :)

regards,
andre



On 27 August 2017 at 11:48, cyrille henry <ch at chnry.net> wrote:

> hello
>
> Le 27/08/2017 à 03:05, andre rc a écrit :
>
>> Hello,
>>
>> I'm trying to apply motion blur only to one geo with gemframebuffer.
>> It works fine until I add a background image: when I switch the
>> gemframebuffer format from RGB to RGBA the amount of motion blur decrease
>> considerably.
>>
> yes, since the feedback image became more and more transparent...
>
>
>
>> Is there a way to get the same amount of motion blur (long tail) with
>> alpha on?
>>
> replace [color 1 1 1 0.95] with [color 0.95 0.95 0.95 1]
>
> but that's not what you want since it will fade to black and not to
> transparent.
>
>
> an other solution would be : you can alter the color of the feedback image
> by drawing a bit of the BG on top of it.
>
> attachment example.
>
> cheers
> c
>
> Attached example.
>>
>> thanks & regards,
>> andre
>>
>>
>>
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