Re: [PD] [Gem] Modifying single pixel of pix image

[Roman Haefeli]

Thank you, Christof and Cyrille, for your insights. I think I
understood the concept. But do I need even framebuffer ping-ponging
when I only _add_ to the framebuffer? Let's say I add more and more
pixel-sized white squares to the buffer, I can use this as my mask, no?

Roman

On Sam, 2017-04-08 at 11:05 +0200, cyrille henry wrote:
> hello,
> I use ping "pong buffer" frequentlly : using 2 framebuffer is a good
> way to go.
> 
> There is an exemple in 10.glsl/07.framebuffer_and_shader : I use a
> "ping pong" to create the wave physical model.
> 
> For your application, you don't even need a shader to alter the image
> : you can draw the image, then draw a pixel size square where you
> want to modify it.
> 
> c
> 
> 
> Le 08/04/2017 à 10:51, Christof Ressi a écrit :
> > 
> > You could also experiment with fragment shader + "ping pong"
> > framebuffers:
> > 
> > shaders usually don't have 'memory' of the last frame(s), so the
> > idea is that you have two framebuffers and *alternately* take one's
> > texture as input and draw to the other framebuffer. this way you
> > can work on the previous frame and manipulate the alpha channel,
> > e.g. subtract values from your alpha pixels based on some random
> > function etc. You can define some uniforms to control the
> > parameters of your decay formula from outside.
> > 
> > Framebuffer ping ponging is easy in openFrameworks, but I have
> > never done it in GEM (honestly I haven't used GEM for a long time
> > now). I guess you can use two [gemframebuffer] objects and switch
> > your connections every other frame...
> > 
> > 
> > > 
> > > Gesendet: Samstag, 08. April 2017 um 10:32 Uhr
> > > Von: "Christof Ressi" <christof.re...@gmx.at>
> > > An: "Roman Haefeli" <reduz...@gmail.com>
> > > Cc: pd-list <pd-l...@iem.at>
> > > Betreff: Re: [PD] [Gem] Modifying single pixel of pix image
> > > 
> > > That's funny, I just did exactly this recently, but in
> > > openFrameworks. If you want to do it entirely in GL (which will
> > > be fastest), this is how I did it:
> > > 
> > > start with a white framebuffer and gradually draw black stuff in
> > > there. Don't clear the framebuffer so it accumulates. You can
> > > even draw with alpha blending to make the decomposition smooth.
> > > Then simply use the texture of the framebuffer as the alpha mask
> > > for your image texture.
> > > 
> > > I couldn't see how to do GL alpha masking in GEM but you can
> > > easily write a little shader which takes the two textures as
> > > uniforms, then you would just need to take one channel of the
> > > mask texture and copy it to the alpha channel of your image
> > > texture.
> > > 
> > > You can also try on the CPU level: create your mask in a table,
> > > make it to a greyscale image and use pix_takealpha to copy your
> > > alpha mask to your image pixels. Of course, this will be much
> > > slower.
> > > 
> > > You can also mix the two approaches: create the mask on the CPU
> > > and do actually masking in GL.
> > > 
> > > Hope that helps!
> > > 
> > > 
> > > > 
> > > > Gesendet: Samstag, 08. April 2017 um 10:02 Uhr
> > > > Von: "Roman Haefeli" <reduz...@gmail.com>
> > > > An: pd-list <pd-l...@iem.at>
> > > > Betreff: Re: [PD] [Gem] Modifying single pixel of pix image
> > > > 
> > > > On Sam, 2017-04-08 at 08:29 +0200, Christof Ressi wrote:
> > > > > 
> > > > > If it can be on the GPU, use a fragment shader! Do you work
> > > > > with a
> > > > > formula or do you set the alpha values by hand?
> > > > By Hand (maybe later by a formula). Is it possible?
> > > > 
> > > > The idea is to have two overlaying images. The visible one
> > > > slowly
> > > > decomposes over time so that the image behind appears. I
> > > > thought about
> > > > setting alpha to for more and more pixels as a way to decompose
> > > > the
> > > > front image. Maybe there is another/better way?
> > > > 
> > > > Roman
> > > > 
> > > > 
> > > > > 
> > > > > > 
> > > > > > Gesendet: Freitag, 07. April 2017 um 23:39 Uhr
> > > > > > Von: "Roman Haef

Re: [PD] [Gem] Modifying single pixel of pix image

[cyrille henry]

hello,
I use ping "pong buffer" frequentlly : using 2 framebuffer is a good way to go.

There is an exemple in 10.glsl/07.framebuffer_and_shader : I use a "ping pong" 
to create the wave physical model.

For your application, you don't even need a shader to alter the image : you can 
draw the image, then draw a pixel size square where you want to modify it.

c


Le 08/04/2017 à 10:51, Christof Ressi a écrit :

You could also experiment with fragment shader + "ping pong" framebuffers:

shaders usually don't have 'memory' of the last frame(s), so the idea is that 
you have two framebuffers and *alternately* take one's texture as input and 
draw to the other framebuffer. this way you can work on the previous frame and 
manipulate the alpha channel, e.g. subtract values from your alpha pixels based 
on some random function etc. You can define some uniforms to control the 
parameters of your decay formula from outside.

Framebuffer ping ponging is easy in openFrameworks, but I have never done it in 
GEM (honestly I haven't used GEM for a long time now). I guess you can use two 
[gemframebuffer] objects and switch your connections every other frame...



Gesendet: Samstag, 08. April 2017 um 10:32 Uhr
Von: "Christof Ressi" <christof.re...@gmx.at>
An: "Roman Haefeli" <reduz...@gmail.com>
Cc: pd-list <pd-l...@iem.at>
Betreff: Re: [PD] [Gem] Modifying single pixel of pix image

That's funny, I just did exactly this recently, but in openFrameworks. If you 
want to do it entirely in GL (which will be fastest), this is how I did it:

start with a white framebuffer and gradually draw black stuff in there. Don't 
clear the framebuffer so it accumulates. You can even draw with alpha blending 
to make the decomposition smooth. Then simply use the texture of the 
framebuffer as the alpha mask for your image texture.

I couldn't see how to do GL alpha masking in GEM but you can easily write a 
little shader which takes the two textures as uniforms, then you would just 
need to take one channel of the mask texture and copy it to the alpha channel 
of your image texture.

You can also try on the CPU level: create your mask in a table, make it to a 
greyscale image and use pix_takealpha to copy your alpha mask to your image 
pixels. Of course, this will be much slower.

You can also mix the two approaches: create the mask on the CPU and do actually 
masking in GL.

Hope that helps!



Gesendet: Samstag, 08. April 2017 um 10:02 Uhr
Von: "Roman Haefeli" <reduz...@gmail.com>
An: pd-list <pd-l...@iem.at>
Betreff: Re: [PD] [Gem] Modifying single pixel of pix image

On Sam, 2017-04-08 at 08:29 +0200, Christof Ressi wrote:

If it can be on the GPU, use a fragment shader! Do you work with a
formula or do you set the alpha values by hand?


By Hand (maybe later by a formula). Is it possible?

The idea is to have two overlaying images. The visible one slowly
decomposes over time so that the image behind appears. I thought about
setting alpha to for more and more pixels as a way to decompose the
front image. Maybe there is another/better way?

Roman



Gesendet: Freitag, 07. April 2017 um 23:39 Uhr
Von: "Roman Haefeli" <reduz...@gmail.com>
An: pd-list@lists.iem.at
Betreff: [PD] [Gem] Modifying single pixel of pix image

Hi

Is it possible to manipulate a single pixel of a an image loaded by
[pix_image]? Specifically, I'd like to change the alpha value of
certain pixels. It doesn't matter to me whether the manipulation
happens in the pix realm or the GL realm. Currently I can think
only of
cumbersome ways like using [pix_dump] -> [pix_set] and applying the
manipulation to the largish list passed between them. Or by using
[pix_pix2sig~] -> [pix_sig2pix~] which is basically the same, but
would
allow to do the manipulation on a table.

Roman
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Re: [PD] [Gem] Modifying single pixel of pix image

[Christof Ressi]

You could also experiment with fragment shader + "ping pong" framebuffers:

shaders usually don't have 'memory' of the last frame(s), so the idea is that 
you have two framebuffers and *alternately* take one's texture as input and 
draw to the other framebuffer. this way you can work on the previous frame and 
manipulate the alpha channel, e.g. subtract values from your alpha pixels based 
on some random function etc. You can define some uniforms to control the 
parameters of your decay formula from outside.

Framebuffer ping ponging is easy in openFrameworks, but I have never done it in 
GEM (honestly I haven't used GEM for a long time now). I guess you can use two 
[gemframebuffer] objects and switch your connections every other frame...


> Gesendet: Samstag, 08. April 2017 um 10:32 Uhr
> Von: "Christof Ressi" <christof.re...@gmx.at>
> An: "Roman Haefeli" <reduz...@gmail.com>
> Cc: pd-list <pd-l...@iem.at>
> Betreff: Re: [PD] [Gem] Modifying single pixel of pix image
>
> That's funny, I just did exactly this recently, but in openFrameworks. If you 
> want to do it entirely in GL (which will be fastest), this is how I did it: 
> 
> start with a white framebuffer and gradually draw black stuff in there. Don't 
> clear the framebuffer so it accumulates. You can even draw with alpha 
> blending to make the decomposition smooth. Then simply use the texture of the 
> framebuffer as the alpha mask for your image texture.
> 
> I couldn't see how to do GL alpha masking in GEM but you can easily write a 
> little shader which takes the two textures as uniforms, then you would just 
> need to take one channel of the mask texture and copy it to the alpha channel 
> of your image texture.
> 
> You can also try on the CPU level: create your mask in a table, make it to a 
> greyscale image and use pix_takealpha to copy your alpha mask to your image 
> pixels. Of course, this will be much slower.
> 
> You can also mix the two approaches: create the mask on the CPU and do 
> actually masking in GL.
> 
> Hope that helps!
> 
> 
> > Gesendet: Samstag, 08. April 2017 um 10:02 Uhr
> > Von: "Roman Haefeli" <reduz...@gmail.com>
> > An: pd-list <pd-l...@iem.at>
> > Betreff: Re: [PD] [Gem] Modifying single pixel of pix image
> >
> > On Sam, 2017-04-08 at 08:29 +0200, Christof Ressi wrote:
> > > If it can be on the GPU, use a fragment shader! Do you work with a
> > > formula or do you set the alpha values by hand?
> > 
> > By Hand (maybe later by a formula). Is it possible?
> > 
> > The idea is to have two overlaying images. The visible one slowly
> > decomposes over time so that the image behind appears. I thought about
> > setting alpha to for more and more pixels as a way to decompose the
> > front image. Maybe there is another/better way?
> > 
> > Roman
> > 
> > 
> > > > Gesendet: Freitag, 07. April 2017 um 23:39 Uhr
> > > > Von: "Roman Haefeli" <reduz...@gmail.com>
> > > > An: pd-list@lists.iem.at
> > > > Betreff: [PD] [Gem] Modifying single pixel of pix image
> > > > 
> > > > Hi
> > > > 
> > > > Is it possible to manipulate a single pixel of a an image loaded by
> > > > [pix_image]? Specifically, I'd like to change the alpha value of
> > > > certain pixels. It doesn't matter to me whether the manipulation
> > > > happens in the pix realm or the GL realm. Currently I can think
> > > > only of
> > > > cumbersome ways like using [pix_dump] -> [pix_set] and applying the
> > > > manipulation to the largish list passed between them. Or by using
> > > > [pix_pix2sig~] -> [pix_sig2pix~] which is basically the same, but
> > > > would
> > > > allow to do the manipulation on a table.
> > > > 
> > > > Roman 
> > > >  ___
> > > > Pd-list@lists.iem.at mailing list
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Re: [PD] [Gem] Modifying single pixel of pix image

[Christof Ressi]

That's funny, I just did exactly this recently, but in openFrameworks. If you 
want to do it entirely in GL (which will be fastest), this is how I did it: 

start with a white framebuffer and gradually draw black stuff in there. Don't 
clear the framebuffer so it accumulates. You can even draw with alpha blending 
to make the decomposition smooth. Then simply use the texture of the 
framebuffer as the alpha mask for your image texture.

I couldn't see how to do GL alpha masking in GEM but you can easily write a 
little shader which takes the two textures as uniforms, then you would just 
need to take one channel of the mask texture and copy it to the alpha channel 
of your image texture.

You can also try on the CPU level: create your mask in a table, make it to a 
greyscale image and use pix_takealpha to copy your alpha mask to your image 
pixels. Of course, this will be much slower.

You can also mix the two approaches: create the mask on the CPU and do actually 
masking in GL.

Hope that helps!


> Gesendet: Samstag, 08. April 2017 um 10:02 Uhr
> Von: "Roman Haefeli" <reduz...@gmail.com>
> An: pd-list <pd-l...@iem.at>
> Betreff: Re: [PD] [Gem] Modifying single pixel of pix image
>
> On Sam, 2017-04-08 at 08:29 +0200, Christof Ressi wrote:
> > If it can be on the GPU, use a fragment shader! Do you work with a
> > formula or do you set the alpha values by hand?
> 
> By Hand (maybe later by a formula). Is it possible?
> 
> The idea is to have two overlaying images. The visible one slowly
> decomposes over time so that the image behind appears. I thought about
> setting alpha to for more and more pixels as a way to decompose the
> front image. Maybe there is another/better way?
> 
> Roman
> 
> 
> > > Gesendet: Freitag, 07. April 2017 um 23:39 Uhr
> > > Von: "Roman Haefeli" <reduz...@gmail.com>
> > > An: pd-list@lists.iem.at
> > > Betreff: [PD] [Gem] Modifying single pixel of pix image
> > > 
> > > Hi
> > > 
> > > Is it possible to manipulate a single pixel of a an image loaded by
> > > [pix_image]? Specifically, I'd like to change the alpha value of
> > > certain pixels. It doesn't matter to me whether the manipulation
> > > happens in the pix realm or the GL realm. Currently I can think
> > > only of
> > > cumbersome ways like using [pix_dump] -> [pix_set] and applying the
> > > manipulation to the largish list passed between them. Or by using
> > > [pix_pix2sig~] -> [pix_sig2pix~] which is basically the same, but
> > > would
> > > allow to do the manipulation on a table.
> > > 
> > > Roman 
> > >  ___
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Re: [PD] [Gem] Modifying single pixel of pix image

[Roman Haefeli]

On Sam, 2017-04-08 at 08:29 +0200, Christof Ressi wrote:
> If it can be on the GPU, use a fragment shader! Do you work with a
> formula or do you set the alpha values by hand?

By Hand (maybe later by a formula). Is it possible?

The idea is to have two overlaying images. The visible one slowly
decomposes over time so that the image behind appears. I thought about
setting alpha to for more and more pixels as a way to decompose the
front image. Maybe there is another/better way?

Roman


> > Gesendet: Freitag, 07. April 2017 um 23:39 Uhr
> > Von: "Roman Haefeli" 
> > An: pd-list@lists.iem.at
> > Betreff: [PD] [Gem] Modifying single pixel of pix image
> > 
> > Hi
> > 
> > Is it possible to manipulate a single pixel of a an image loaded by
> > [pix_image]? Specifically, I'd like to change the alpha value of
> > certain pixels. It doesn't matter to me whether the manipulation
> > happens in the pix realm or the GL realm. Currently I can think
> > only of
> > cumbersome ways like using [pix_dump] -> [pix_set] and applying the
> > manipulation to the largish list passed between them. Or by using
> > [pix_pix2sig~] -> [pix_sig2pix~] which is basically the same, but
> > would
> > allow to do the manipulation on a table.
> > 
> > Roman 
> >  ___
> > Pd-list@lists.iem.at mailing list
> > UNSUBSCRIBE and account-management -> https://lists.puredata.info/l
> > istinfo/pd-list
> > 

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Re: [PD] [Gem] Modifying single pixel of pix image

[Christof Ressi]

If it can be on the GPU, use a fragment shader! Do you work with a formula or 
do you set the alpha values by hand?

> Gesendet: Freitag, 07. April 2017 um 23:39 Uhr
> Von: "Roman Haefeli" 
> An: pd-list@lists.iem.at
> Betreff: [PD] [Gem] Modifying single pixel of pix image
>
> Hi
> 
> Is it possible to manipulate a single pixel of a an image loaded by
> [pix_image]? Specifically, I'd like to change the alpha value of
> certain pixels. It doesn't matter to me whether the manipulation
> happens in the pix realm or the GL realm. Currently I can think only of
> cumbersome ways like using [pix_dump] -> [pix_set] and applying the
> manipulation to the largish list passed between them. Or by using
> [pix_pix2sig~] -> [pix_sig2pix~] which is basically the same, but would
> allow to do the manipulation on a table.
> 
> Roman 
>  ___
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