you can use sigle buffer rendering.
see example 04.pix/10.pixDataSimple.pd
cyrille
Le 09/04/2017 à 09:23, Roman Haefeli a écrit :
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" <[email protected]>
An: "Roman Haefeli" <[email protected]>
Cc: pd-list <[email protected]>
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" <[email protected]>
An: pd-list <[email protected]>
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" <[email protected]>
An: [email protected]
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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