dscharf@gmx.net

a short question from me. Are there any tricks how one can access the contents (maybe as a texture) of the last frame from inside a fragment shader? Perhaps grabbing the screenbuffer or something like that? I haven't found anything about that on the net so far, so it seems there's no way, but maybe one of you knows.

shaders-accessing-screencontent-of-last-frame

If you use the @capture attribute of a jit.gl object, you can send

> a short question from me. Are there any tricks how one can access the contents (maybe as a texture) of the last frame from inside a fragment shader? Perhaps grabbing the screenbuffer or something like that? I haven't found anything about that on the net so far, so it seems there's no way, but maybe one of you knows.

If you use the @capture attribute of a jit.gl object, you can send
whatever is drawn to a texture.

On 7/18/07, Dave  wrote:
>
> Hi all,
>
> a short question from me. Are there any tricks how one can access the contents (maybe as a texture) of the last frame from inside a fragment shader? Perhaps grabbing the screenbuffer or something like that? I haven't found anything about that on the net so far, so it seems there's no way, but maybe one of you knows.
>
> Thanks
>
> Dave
>


Is it some kind of feedback effect u're trying to accomplish?

What about making a shader with 2 inputs? one (the left input?) with the

current frame, one with the previous frame. That way you'll be able to

change the delay between the two frames from outside the shader...

> a short question from me. Are there any tricks how one can access the

> contents (maybe as a texture) of the last frame from inside a fragment

> shader? Perhaps grabbing the screenbuffer or something like that? I haven't

> found anything about that on the net so far, so it seems there's no way, but

Is it some kind of feedback effect u're trying to accomplish?
What about making a shader with 2 inputs? one (the left input?) with the
current frame, one with the previous frame. That way you'll be able to
change the delay between the two frames from outside the shader...
Or didn't i understand you correctly?

On 7/18/07, Dave  wrote:
>
>
> Hi all,
>
> a short question from me. Are there any tricks how one can access the
> contents (maybe as a texture) of the last frame from inside a fragment
> shader? Perhaps grabbing the screenbuffer or something like that? I haven't
> found anything about that on the net so far, so it seems there's no way, but
> maybe one of you knows.
>
> Thanks
>
> Dave
>

thanks for the quick reply. I'm fiddling around right now, hopefully one of your suggestions work for me.

Hey Wes and Mojo,
thanks for the quick reply. I'm fiddling around right now, hopefully one of your suggestions work for me.


Yeah, @capture of you can use render to texture to get the whole 

frame to work. I think ive posted a patch or two showing GL feedback 

> thanks for the quick reply. I'm fiddling around right now, 

> hopefully one of your suggestions work for me.

Yeah, @capture of you can use render to texture to get the whole  
frame to work. I think ive posted a patch or two showing GL feedback  
with slab processing etc.
On Jul 18, 2007, at 5:32 AM, Dave wrote:

>
> Hey Wes and Mojo,
> thanks for the quick reply. I'm fiddling around right now,  
> hopefully one of your suggestions work for me.

There are several ways to do OpenGL-based texture feedback, many of

which are covered in the examples folder and the Jitter Recipes. I've

been kicking around the idea of doing an article on feedback, but

There are several ways to do OpenGL-based texture feedback, many of
which are covered in the examples folder and the Jitter Recipes.  I've
been kicking around the idea of doing an article on feedback, but
haven't gotten around to it yet.

Quote: andrewb@cycling74.com wrote on Wed, 18 July 2007 18:48

----------------------------------------------------

> There are several ways to do OpenGL-based texture feedback, many of

> which are covered in the examples folder and the Jitter Recipes. I've

> been kicking around the idea of doing an article on feedback, but

At one point I'd love to see an article highlighting the differences between the approaches, since I personally only "master" one way, that I've cobbled together from a user-example... Being able to get under the skin of the various methods would be killer.

Quote: andrewb@cycling74.com wrote on Wed, 18 July 2007 18:48
----------------------------------------------------
> There are several ways to do OpenGL-based texture feedback, many of
> which are covered in the examples folder and the Jitter Recipes.  I've
> been kicking around the idea of doing an article on feedback, but
> haven't gotten around to it yet.
>
> Andrew B.
>
----------------------------------------------------
At one point I'd love to see an article highlighting the differences between the approaches, since I personally only "master" one way, that I've cobbled together from a user-example... Being able to get under the skin of the various methods would be killer.

use to_texture and capture the whole scene, render to a video plane 

    adjusting the alpha value of the erase_color (wont work with FSAA :( )

    and adjusting the scale/position/rotation of the videoplane to 

produce the regular video feedback (camera pointed towards monitor 

use slab based feedback and use a compositing shader and use a 

similar technique with xfadeshader(a) -> rotashader(or whatever) ->

xfadeshader (b). param mixamount is the amount of feedback. swap out 

whatever xfade shader you want for differing blend modes etc.

As far as I know, those are the two main approaches. I actually use 

both in my patches, since each has a unique feel to it.

On Jul 19, 2007, at 12:46 PM, Andreas Wetterberg wrote:

> Quote: andrewb@cycling74.com wrote on Wed, 18 July 2007 18:48

> ----------------------------------------------------

>> There are several ways to do OpenGL-based texture feedback, many of

>> which are covered in the examples folder and the Jitter Recipes. 

>> been kicking around the idea of doing an article on feedback, but

> At one point I'd love to see an article highlighting the 

> differences between the approaches, since I personally only 

> "master" one way, that I've cobbled together from a user-example... 

> Being able to get under the skin of the various methods would be 

use to_texture and capture the whole scene, render to a video plane  
and produce feedback by:

	adjusting the alpha value of the erase_color (wont work with FSAA :( )
	and adjusting the scale/position/rotation of the videoplane to  
produce the regular video feedback (camera pointed towards monitor  
style effects)

  use slab based feedback and use a compositing shader and use a  
similar technique with xfadeshader(a) -> rotashader(or whatever) ->
xfadeshader (b). param mixamount is the amount of feedback. swap out  
whatever xfade shader you want for differing blend modes etc.

As far as I know, those are the two main approaches. I actually use  
both in my patches, since each has a unique feel to it.

>
> Quote: andrewb@cycling74.com wrote on Wed, 18 July 2007 18:48
> ----------------------------------------------------
>> There are several ways to do OpenGL-based texture feedback, many of
>> which are covered in the examples folder and the Jitter Recipes.   
>> I've
>> been kicking around the idea of doing an article on feedback, but
>> haven't gotten around to it yet.
>>
>> Andrew B.
>>
> ----------------------------------------------------
> At one point I'd love to see an article highlighting the  
> differences between the approaches, since I personally only  
> "master" one way, that I've cobbled together from a user-example...  
> Being able to get under the skin of the various methods would be  
> killer.
>
> Andreas.
>

I use a similar technique to your approach a) and i get it to work with fsaa turned on. I alter the texture scale and rotate it within videoplane and don't rely on the alpha value of the erase colour to increase the feedback amount. Instead I use the alpha value of the videoplane colour.

I've been working on some patches to release that are on my website at the moment but haven't publicised it yet because I want to check a few things, but hey, I've told you now! Check out the example patch in the tools package - i use this method there.

http://www.pelado.co.uk/category/maxmspjitter/

I use a similar technique to your approach a) and i get it to work with fsaa turned on.  I alter the texture scale and rotate it within videoplane and don't rely on the alpha value of the erase colour to increase the feedback amount.  Instead I use the alpha value of the videoplane colour.  

I've been working on some patches to release that are on my website at the moment but haven't publicised it yet because I want to check a few things, but hey, I've told you now!  Check out the example patch in the tools package - i use this method there.

Shaders: Accessing screencontent of last frame